Country：Japan

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Journal of Materials Chemistry A  

Co-electrolysis of H2O and N/C sources to valuable chemicals has the potential to contribute to global warming mitigation. We here report the electrochemical conversion of H2O and CO2 into methanol in a gas flow system at temperatures between 100 and 200 °C. CO2 was reduced to methane with voltage-boosted H2 at a Ru/C cathode. Introduced Fe2O3 nanoparticles promoted the adsorption and activation of CO2 on the surface of Ru because of their high redox activity. Methane was oxidized to methanol through the formation of ˙CH3 and active oxygen species at a Pt anode. The addition of Au to the anode enhanced the selectivity toward methanol by reducing the activity of Pt in the complete oxidation of methanol. Combining these processes with gas penetration into the electrolyte membrane enabled the synthesis of methanol from H2O and CO2, with a maximum faradaic efficiency of 54%. This work establishes a methodology for providing a good balance between the activity and selectivity of electrodes for the CO2 reduction reaction.

DOI： 10.1039/d2ta04011e

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Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.1246/cl.210321

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Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.electacta.2021.138681

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Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.1021/acssuschemeng.0c07657

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Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.1039/d0cc04789a

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Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.1039/d0ta04866f

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Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.wasman.2019.10.019

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Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.3390/catal10010106

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Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.3390/ma12223701

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Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.ijhydene.2018.12.044

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Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.1038/s41598-018-34544-y

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Applied Catalysis B: Environmental  

Biomass electrolysis enables hydrogen (H2) production at onset voltages of less than 1 V, depending on the fuel species. However, biofuel derived from biomass not categorized as food and produced from environmentally friendly processes is needed for the development of sustainable strategies. In addition, the biofuel should not require special and expensive procedures for processing. The present report describes the direct electrolysis of waste newspaper for H2 production. Cellulose and lignin included in the newspaper were subject to dissolution and hydrolysis in a phosphoric acid solvent at the anode in a temperature range of 100–175 °C. The resulting decomposition products were electrolyzed to H2 and carbon dioxide (CO2), at low onset voltages (ca. 0.2 V) and high current efficiencies (H2: 1.0, CO2: 0.9). Carbon black functionalized with carbonyl groups showed greater catalytic activity than a Pt/C catalyst for the anode reaction. H2 yield reached ca. 0.2 g per 1 g of newspaper in a batch cell. H2 was produced continuously in a current-density range of 0.15–0.25 A cm−2 while maintaining plateau-like voltage behavior in a flow cell. The energy consumed for electrolysis at a current density of 0.15 A cm−2 was as low as 1.27 kWh (Nm3)−1.

DOI： 10.1016/j.apcatb.2018.03.021

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Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.1021/acssuschemeng.8b01701

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Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.1002/celc.201700917

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Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.1246/bcsj.20170163

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Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.1149/2.0361709jes

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Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.1149/2.0511706jes

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Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.1038/srep37463

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Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.1038/srep31691

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Chemistry Letters  

SnSO4 was employed as an anode-active material for rechargeable batteries, where Sn4+ and Sn2+ ions are reduced to Sn2+ and Sn, respectively during charge while the inverse reactions occur during discharge. Undesired hydrogen production was substantially avoided by adjusting the charge voltage to 1.5V. The resulting cell functioned as a battery with an electrical capacity of 258mA hg-1 at 10mA cm-2 and as a fuel cell with power densities of 55-125 mW cm-2 at 0.8V.

DOI： 10.1246/cl.151015

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Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.1002/celc.201500473

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Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.1149/2.1341607jes

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Journal of the Electrochemical Society  

There have been many attempts to develop solid-state sensor devices for detecting particulate matter (PM) in diesel exhaust; however, in most of these, the accumulated PM must be burned intermittently to allow subsequent sensing cycles. Here, we report a self-regenerable PM sensor using a proton conductive solid electrolyte and an active working electrode for PM oxidation. The withstanding voltage capability of BaZr0.8Y0.2O3-δ was greatly improved by the growth of a dense Zr1-xYxP2O7 film on the electrolyte surface. The reaction of PM with active oxygen under anodic polarization was further enhanced by the addition of IrO2 to the working electrode. As a result of these combined modifications, when the working electrode was anodically polarized, PM was oxidized to CO2 according to a four-electron reaction (C + 2H2O → CO2 + 4H+ + 4e-) while remaining below the self-ignition temperature. This amperometric sensor successfully produced a current signal corresponding to the quantity of PM in a gas stream at an operating temperature of 300°C. These results demonstrate that the sensor can carry out continuous monitoring of PM concentrations while self-regenerating.

DOI： 10.1149/2.1281614jes

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Authorship：Lead author   Language：Japanese  

Authorship：Lead author   Language：Japanese  

Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.1246/cl.141067

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Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.1038/srep07903

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Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.1149/2.0611504jes

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Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.1149/2.0581508jes

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Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.1039/c5cc04286k

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Chemistry Letters  

The effect of the addition of copper-doped bismuth-vanadium oxide to yttria-stabilized zirconia (YSZ) on the sinterability and electrical conductivity, especially in reducing atmospheres, has been investigated. When Bi2Cu0.1V0.9O5.35 was used as a sintering aid, the sintering temperature could be reduced to 800°C, whereas the conventional sintering process requires temperatures above 1300°C. Although the conductivity of YSZ with 1.5 mol% Bi2Cu0.1V0.9O5.35 was slightly lower than that of pure YSZ si ntered at 1300°C, no PO2 dependence was observed under reducing conditions (e.g., PO2 = 10-5-10-24 atm), which indicates that the electrolyte is applicable to solid-oxide fuel cells.

DOI： 10.1246/cl.140712

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Angewandte Chemie - International Edition  

Reported herein is an electrode for dihydrogen (H2) oxidation, and it is based on [NiFe]Hydrogenase from Citrobacter sp. S-77 ([NiFe] S77). It has a 637 times higher mass activity than Pt (calculated based on 1 mg of [NiFe]S77 or Pt) at 50 mV in a hydrogen half-cell. The [NiFe]S77 electrode is also stable in air and, unlike Pt, can be recovered 100% after poisoning by carbon monoxide. Following characterization of the [NiFe]S77 electrode, a fuel cell comprising a [NiFe] S77 anode and Pt cathode was constructed and shown to have a a higher power density than that achievable by Pt. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

DOI： 10.1002/anie.201404701

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Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.electacta.2013.08.107

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Journal of the Electrochemical Society  

Themixed potential response for various hydrocarbons at room temperaturewas investigated using proton-conductive Sn0.9In0.1P 2O7 as an electrolyte. Among the tested electrodes, Pt/C exhibited the most negative potential in a feed mixture of 1000 ppm propene, 10% oxygen, and ca. 3% water vapor. The potential of this electrode was further shifted to a more negative value by the addition of Sn0.9In 0.1P2O7 to the electrode. The resultant potential vs. an air electrode reached ?78 mV at 1000 ppm propene, which is a significant deviation from that calculated from the Nernst equation. This non-Nernstian potential also became enhanced as the concentration and carbon number of the hydrocarbon increased, with the C-C linkage unsaturated, and with a branched chain structure. These enhancement effects could be explained by the polarization curves for hydrocarbon and oxygen, where CO2 formation through hydrocarbon oxidation and water vapor formation through oxygen reduction were in competition with each other. It should be emphasized that the heterogeneous catalytic reaction of the hydrocarbon with oxygen did not occur over the electrode, which allowed not only for a simple mixed potential theory, but also for the potential properties to be independent of the supply gas flow rate. © 2014 The Electrochemical Society. All rights reserved.

DOI： 10.1149/2.054405jes

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Journal of Materials Chemistry A  

DOI： 10.1039/c3ta90280c

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Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.electacta.2013.08.101

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：ChemCatChem  

We report the successful increase in performance of a fuel cell based on organometallic catalysis. An organometallic [NiIIRuIV] peroxo complex functions as cathode catalyst and was designed following mechanistic consideration of the cell. It was confirmed that the organometallic [NiIIRuIV] peroxo catalyst could function in the fuel cell with a 240% increase in power output over our previous systems. This organometallic catalyst can act in both solid and solution phases and allows observation of the mechanism, hence providing us further opportunity for future improvement. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

DOI： 10.1002/cctc.201200595

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Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.1021/jp312213x

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Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.1039/c2ta00368f

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Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.1039/c3ta10769h

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Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.1039/c3ta11118k

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Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.1039/c3ta12525d

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Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.1039/c3ta12707a

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Journal of Materials Chemistry A  

Ammonium proton in a solid ionic semiconductor, TTFCOONH4, is shown to be mobile under anhydrous conditions at room temperature by the hydrogen concentration cell method. Isotope substituted TTFCOOND4 exhibits a 2.2 H/D isotope effect in ion carrier mobility with TTFCOONH 4. First-principles calculations reveal that an efficient proton-transfer pathway via low-barrier N⋯H+⋯N hydrogen bonds reduces the activation energy to 0.12 eV, which is quite small and comparable to that reported in a bulk water system. The ac conductivity of TTFCOONH4 and TTFCOOND4 is similar at room temperature, reflecting similar hole carrier concentrations. In sharp contrast, the thermopower exhibits a large isotope effect: TTFCOONH4 shows 260 μV K-1, which is twice as large as that predicted by the hole carrier concentration and the value of TTFCOOND4, with 138 μV K-1. The 1.9 H/D isotope effect in thermopower closely relates to the 2.2 H/D isotope effect in ion carrier mobility. Proton carriers in the temperature gradient enhance thermopower without cancelling out the effect of holes in the solid state owing to possession of the same positive charge. © The Royal Society of Chemistry 2013.

DOI： 10.1039/c3ta00011g

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Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.elecom.2012.08.020

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Authorship：Lead author   Language：Japanese  

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Sensors and Actuators, B: Chemical  

The carbon oxidation activity and sensing performance of an electrochemical sensor incorporating a robust SnP 2O 7-SnO 2 composite ceramic as a solid electrolyte were investigated at an operating temperature of 200°C. Specific reactivity of the electrochemically formed active oxygen toward carbon was accomplished with a high current efficiency estimated from the four-electron reaction (C + 2H 2O → CO 2 + 4H + + 4e -). However, this reaction did not occur over the entire electrode layer, which resulted in low sensitivity and a slow response speed. This problem could be overcome by distributing a SnP 2O 7 ionomer over the working electrode at a level of several micrometers. Moreover, an additional benefit of the present sensor for practical applications is that little interference was encountered when sensing carbon at levels of 1000 ppm CO and 1000 ppm C 3H 8 in the sample gas. The resulting amperometric mode sensor could successfully produce a current signal that corresponded to the quantity of particulate matter (PM) in the bench test apparatus. These results demonstrate that the present sensor is able to continuously monitor the PM concentration while self-regenerating. © 2011 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.snb.2011.12.057

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Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.1002/anie.201202159

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Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.1039/c2jm31887c

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Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.1002/anie.201205022

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Angewandte Chemie - International Edition  

Gas-phase electrochemistry: The direct hydroxylation of benzene to phenol was investigated using an electrochemical cell. The production of phenol over a VO x anode was found to be significant at 50 °C. The resultant current efficiency for phenol production and selectivity toward phenol reached 76.5 and 94.7 %, respectively. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

DOI： 10.1002/anie.201105229

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Journal of Materials Chemistry  

Proton conductors capable of operating in the temperature range of 100-600°C have received great interest for many application areas such as fuel cells, sensors, and electrolyzers; however, very few materials that can satisfy these demands have been reported to date. Here, we report a promising candidate for a solid electrolyte in intermediate-temperature electrochemical devices. First, MP 2O 7-MO 2 composite ceramics (M = Sn, Si, Ti, and Zr) were prepared by reacting a porous MO 2 substrate with an 85% H 3PO 4 solution at 600°C. Although all the tested MO 2 could react with H 3PO 4 to form the corresponding metal pyrophosphate layers on the surfaces of the exterior and interior substrate, the extent of MP 2O 7 growth in the obtained samples and their relative density were strongly dependent on the M species. These factors were the best for the SnP 2O 7-SnO 2 composite ceramic, yielding the highest electrical conductivity in the temperature range of interest. Next, different low valence cations (cation = Mg 2+, Sc 3+, Ga 3+, Y 3+, In 3+, La 3+, Sm 3+, Eu 3+, and Gd 3+) were doped into the SnP 2O 7-SnO 2 composite ceramic. The most positive effect on the electrical conductivity was observed when Sm 3+ was used as the dopant; the electrical conductivity of this sample was approximately one order of magnitude higher than that of the non-doped sample, especially at low temperatures below 250°C. Fourier transform infrared (FTIR) and proton magic angle spinning (MAS) nuclear magnetic resonance (NMR) analyses revealed that the quantity of protons incorporated in the SnP 2O 7 layer and their mobility were increased by the doping of Sm into the composite ceramic. As a consequence, the electrical conductivity of the Sm-doped SnP 2O 7-SnO 2 composite ceramic reached ∼10 -2 S cm -1 in the temperature range of 100-600°C. Proton conduction in this sample was also investigated by various electrochemical techniques. The protons function as the predominant charge carrier in the sample, and the proton transport number was almost unity in both static and dynamic conditions. © 2012 The Royal Society of Chemistry.

DOI： 10.1039/c2jm15335a

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Authorship：Lead author   Language：Japanese  

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Journal of the Ceramic Society of Japan  

The development of proton conductors has proceeded rapidly in recent years. A number of organic or inorganic materials show proton conductivities of ∼10-2Scm-1 at temperatures below 100°C. However, although there is great current demand for proton conductors capable of operating in the temperature range of 100400° C in practical applications, very few materials that can satisfy this demand have been reported to date. Acceptor-doped SnP2O7 are promising candidate materials because their proton conductivities reach >10-1Scm-1 in the temperature range of interest. This paper presents an overview of the current status of acceptor-doped SnP2O7, highlighting the mechanism and kinetics of proton conduction and the development of electrochemical devices using these materials. New insights for proton insertion and conduction are proposed that use electrochemical techniques. Two approaches to designing SnP2O7-based composite electrolytes with good mechanical properties have also been developed for different operating temperatures. In addition, the benefits of intermediate-temperature operation using these materials are discussed in terms of practical applications, especially in fuel cells, exhaust sensors, and solid catalysts. © 2011 The Ceramic Society of Japan. All rights reserved.

DOI： 10.2109/jcersj2.119.677

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Applied Catalysis B: Environmental  

Propane oxidation and NO reduction at the proton conductor-electrocatalyst interface were investigated using electrochemical cells and impregnated catalysts. Sn0.9In0.1P2O7 and Pt or Pt-Rh were used as the proton conductor and electrocatalyst, respectively. In a gaseous mixture of propane, H2O, and NO, H2O is dissociated into protons and electrons at anodic sites at the interface and the resultant active oxygen oxidizes propane to CO2. Separately, NO reacts with protons and electrons to form N2O at cathodic sites at the interface. Under stoichiometric conditions, including 1000ppm propane, 1000ppm NO, 3% H2O, and 4500ppm O2, the temperatures at which the above series of reactions could successfully achieve 50% conversion (T50%) was reduced to 310 and 385°C for propane and NO, respectively, over a 0.01wt.% Pt/Sn0.9In0.1P2O7 catalyst. These were much lower than T50% of 430 and 535°C for propane and NO, respectively, over a 0.01wt.% Pt/γ-Al2O3 catalyst. Moreover, the addition of 0.005wt.% Rh to the Pt/Sn0.9In0.1P2O7 catalyst enhanced NO reduction by promoting the dissociative adsorption of NO, thus providing a further reduction of T50% for the NO reaction to 355°C. © 2011 Elsevier B.V.

DOI： 10.1016/j.apcatb.2011.06.009

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Journal of Power Sources  

A polybenzimidazole (PBI)/Sn0.95Al0.05P 2O7 (SAPO) composite membrane was synthesized by an in situ reaction of SnO2 and Al(OH)3-mixed powders with an H3PO4 solution in a PBI membrane. The formation of a single phase of SAPO in the PBI membrane was completed at a temperature of 250 °C. Thermogravimetric analysis showed that the PBI membrane was not subject to a serious damage by the presence of SAPO until 500 °C. Scanning electron microscopy revealed that SAPO particles with a diameter of approximately 300 nm were homogeneously dispersed and separated from each other in the PBI matrix. Proton magic angle spinning nuclear magnetic resonance spectra confirmed the presence of new protons originating from the SAPO particles in the composite membrane. As a consequence of the interaction of protons in the SAPO with those in the free H3PO4, the H3PO4-doped PBI/SAPO composite membrane exhibited conductivities several times higher than those of an H3PO4-doped PBI membrane at room temperature to 300 °C, which could contribute to the improved performance of H 2/O2 fuel cells. © 2011 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jpowsour.2011.03.094

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Journal of Power Sources  

New Pt/C cathodes with many reaction sites for the oxygen reduction reaction as well as high tolerance to Pt corrosion have been designed for high-temperature proton exchange membrane fuel cells (PEMFCs), wherein a composite mixture of Sn0.9In0.1P2O7 (SIPO) and sulfonated polystyrene-b-poly(ethylene/butylene)-b-polystyrene (sSEBS) functioned as an ionomer. The microstructure of the Pt-SIPO-sSEBS/C cathode was characterized by homogeneous distribution of the ionomer over the catalyst layer and close contact between the ionomer and the Pt/C powder. As a result, the activation and concentration overpotentials of the Pt-SIPO-sSEBS/C cathode between 100 and 200 °C were lower than those of an H 3PO4-impregnated Pt/C cathode, which suggests that the present ionomer can avoid poisoning of Pt by phosphate anions and the limitation of gas diffusion through the catalyst layer. Moreover, agglomeration of Pt in the Pt-SIPO-sSEBS/C cathode was not observed during a durability test at 150 °C for 6 days, although it was significant in the Pt-H3PO 4/C cathode. Therefore, it is concluded that the Pt-SIPO-sSEBS/C electrode is a very promising cathode candidate for high-temperature PEMFCs. © 2011 Elsevier B.V.

DOI： 10.1016/j.jpowsour.2011.02.028

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Journal of Catalysis  

Direct oxidation of methane to methanol at low temperatures was investigated using a fuel cell-type reactor, where a mixture of methane and H2O vapor was supplied to the anode and air to the cathode. Methanol was scarcely produced over a Pt/C anode from 50 to 250 °C. However, through trial and error, the production of methanol over a V2O 5/SnO2 anode was significant at 100 °C; the current efficiency for methanol production and the selectivity toward methanol were as high as 61.4% and 88.4%, respectively. Methanol was produced by the reaction of methane with an active oxygen species over the V2O5 catalyst. Cyclic voltammetry of the anode indicated that the generation of such active oxygen species was strongly dependent on the anode potential. Moreover, X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy measurements confirmed that highly dispersed and partially reduced vanadium species were present on the SnO2 surface. These vanadium species are considered to be active sites for the formation of the active oxygen species, probably anion radicals (O2·- and O·-). © 2010 Elsevier Inc. All rights reserved.

DOI： 10.1016/j.jcat.2010.12.020

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Authorship：Lead author   Language：Japanese  

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Sensors and Actuators, B: Chemical  

In a previous sensor device based on a PtSn0.9In 0.1P2O7Pt electrode system, electrochemical carbon oxidation was realized over the surface of a working electrode, enabling continuous carbon monitoring with self-regeneration of the sensor. Specific reactivity of the active oxygen species for carbon was demonstrated along with a high current efficiency. However, this reaction did not occur over the entire electrode layer, limiting the sensing properties and giving a low sensitivity and response speed. The main reason for carbon oxidation being limited to the surface region was the lack of proton conduction in the working electrode. To overcome this problem, we added proton-conducting Sn0.9In 0.1P2O7 particles as an ionomer to the working electrode. The Sn0.9In0.1P2O7 ionomer was successfully distributed over the working electrode at the level of a few micrometers, providing reaction sites for carbon oxidation over the entire electrode layer. The resulting amperometric sensor provided a sensitivity to carbon that was 1.4 times greater than that of the ionomer-free working electrode, as determined by the current at which carbon oxidation had ceased. Moreover, carbon floating in a glass container could be transported to reaction sites present on the external surface of the working electrode, allowing for a large current and a rapid response. © 2010 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.snb.2010.10.042

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Chemical Communications  

Fuel cells with a PtAu/C anode and a Pr-doped Mn2O3/C cathode were stacked without using a bipolar plate, and their discharge properties were investigated in a methanol aqueous solution bubbled with air. A three-cell stack exhibited a stack voltage of 2330 mV and a power output of 21 mW. © The Royal Society of Chemistry 2011.

DOI： 10.1039/c1cc10493d

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Journal of Materials Chemistry  

Dense SnP2O7-SnO2 composite ceramics were prepared by reacting a porous SnO2 substrate with an 85% H3PO4 solution at elevated temperatures. At 300 °C and higher, SnO2 reacted with H3PO4 to form an SnP2O7 layer on exterior and interior surfaces in the substrate, the growth rate of which increased with increasing reaction temperature. Finally, at 600 °C, the pores of this composite ceramic were perfectly closed and its electrical conductivity became several orders of magnitude higher than that of the SnO2 substrate alone. Proton conduction was demonstrated in this composite ceramic using electrochemical measurements and various analytical techniques. Comparison of the observed electromotive force with the theoretical value in two gas concentration cells demonstrated that this composite ceramic is a pure ion conductor, wherein the predominant ion species are protons. Fourier transform infrared (FT-IR) and proton magic angle spinning (MAS) nuclear magnetic resonance (NMR) analyses revealed that the protons interacted with lattice oxide ions in the SnP2O7 layer to form hydrogen bonds. An H/D isotope effect suggested that proton conduction in this composite ceramic was based on a proton-hopping mechanism. The proton conductivity in this material reached ∼10-2 S cm-1 in the temperature range of 250-600 °C. © The Royal Society of Chemistry.

DOI： 10.1039/c0jm02596h

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Electrochimica Acta  

An anhydrous proton conductor, Sn0.95Al0.05P 2O7 (SAPO), composed of polystyrene-b-poly(ethylene/ propylene)-b-polystyrene (SEPS), was developed and characterized using morphological, structural, and electrochemical analyses. In the composite membrane with 20 wt% SEPS, a homogeneous distribution of SAPO particles in the matrix was obtained in the thickness range of 65-90 μm, yielding a proton conductivity of 3.4 × 10-3 S cm-1 at 200 °C, tensile strength of 4.6 MPa and an elongation at break of 711.0% at room temperature. Fuel cell tests verified that the open-circuit voltage was maintained at a constant value of approximately 1 V between 100 and 250 °C. The peak power densities achieved with unhumidified H2 and air were 77.0 mW cm-2 at 100 °C, 121.0 mW cm-2 at 150 °C, and 163.1 mW cm-2 at 225 °C. © 2010 Elsevier Ltd All rights reserved.

DOI： 10.1016/j.electacta.2010.07.043

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Energy and Environmental Science  

Fuel cells for vehicular and residential applications have encountered a key technical challenge in cost reduction. This challenge can be avoided by operating a fuel cell stack without the use of gas separators, which are expensive and voluminous and therefore comprise a significant portion of the cost of a fuel cell stack. Single-chamber fuel cells (SCFCs) have the potential of realizing such operation, because there is no need for separation between fuel and air. In this paper, we present a selective anode (PtAu/C) and cathode (Pr-doped Mn2O3/C) for respective electrochemical hydrogen oxidation and oxygen reduction reactions in a SCFC. A single cell with these electrodes operated at 50 °C generated an open-circuit voltage of 1204 mV and a peak power density of 50 mW cm-2 in a feed mixture of 80% hydrogen and 20% air at a flow rate of 30 mL min-1. The high selectivity of these electrodes also enabled the design of two different separator-free fuel cell stacks, parallel and perpendicular to the gas stream. Both cell stacks exhibited increasing stack voltage and power output almost proportionally to the increase in the number of single cells. These results demonstrate that the separator-free fuel cell stack shows high potential for a significant reduction of the cost of fuel cell systems. © The Royal Society of Chemistry.

DOI： 10.1039/c0ee00288g

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Journal of the Japan Petroleum Institute  

Much attention has been devoted to efforts to operate polymer electrolyte fuel cells (PEFCs) at temperatures above 100°C in order to avoid the problem of serious CO poisoning of the anode catalyst. It is also of great con cern to operate PEFCs under low-humidity conditions, because the space and energy required for external humidi fication are eliminated or minimized in the fuel cell system. Thus, proton-conducting materials that can satisfy the above criteria have been proposed, developed, and evaluated worldwide. In particular, recent research efforts have been increasingly focusing on the design of anhydrous proton conductors, since these materials, at least in principle, do not need the presence of water as a charge carrier. We have recently found that In, Al, or Mg-doped SnP2O7 show high proton conductivities>10-1 S. cm-1 between 150 and 350 °C under water-free conditions. Attempts to apply these materials as electrolytes in some electrochemical devices were also made. This paper presents an overview of the current status of doped SnP22O 7 with principal emphasis on the materials aspect. In addition, the benefits of intermediate-temperature fuel cells using these materials are briefy summarized in terms of cell design, electrolyte and electrode materials.

DOI： 10.1627/jpi.53.12

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Applied Catalysis B: Environmental  

Catalytic carbon combustion is a potential approach for eliminating particulate matter emissions from diesel engine vehicles. In this study, we report low-temperature carbon combustion by active oxygen formed at the interface of the mixed powders of a proton conductor (Sn0.9In0.1P2O7) and electrocatalyst (Pt or Mo2C). In a gaseous mixture of H2O and O2, H2O dissociated into protons and electrons at an anodic site of the interface and the resultant active oxygen oxidized carbon to CO2. Separately, O2 reacted with protons and electrons to form H2O at a cathodic site of the interface, resulting in formation of a local electrochemical cell at the proton conductor-electrocatalyst interface, which then self-discharged. This series of reactions could successfully reduce the ignition temperature for carbon to 200°C for Pt and 300°C for Mo2C. © 2010 Elsevier B.V.

DOI： 10.1016/j.apcatb.2010.07.032

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Fuel Cells  

This paper presents a promising approach to reduce the quantity of Pt required in cathodes for high-temperature proton exchange membrane (PEM) fuel cells. Based on preliminary experiments, thermally stable Si 0.97Al0.03C and Sn0.95In0.05P 2O7 were selected as promoter and ionomer, respectively. Si0.97Al0.03C particles (∼40 nm) and Sn 0.95In0.05P2O7 particles (∼45 nm) were successfully produced on a carbon support. Pt particles (∼9 nm) were selectively impregnated in the vicinity of the ionomer. Polarisation measurements revealed that the Pt-Sn0.95In0.05P 2O7-Si0.97Al0.03C/C cathode exhibited much higher oxygen reduction reaction (ORR) activity than that observed for a pure Pt/C cathode, due to the enhanced dissociative oxygen adsorption on the Si0.97Al0.03C particles and the increased number of reaction sites for the ORR provided by the Sn 0.95In0.05P2O7 particles. Fuel cell operation tests demonstrated that a Pt-Sn0.95In0.05P 2O7-Si0.97Al0.03C/C cathode with a low Pt loading of 0.1 mg cm-2 provides better cell performance than a Pt/C cathode with a Pt loading of 1.0 mg cm-2. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

DOI： 10.1002/fuce.200900162

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Journal of Catalysis  

Catalytic combustion of hydrocarbons is a highly active field of research, particularly in relation to the reduction of pollutant emissions from automobiles. In this study, we report on hydrocarbon oxidation at the internal interfaces of a mixed catalyst consisting of Sn0.9In 0.1P2O7 and Pt powders. In a gaseous mixture of propane, H2O, and O2, the H2O dissociates into protons, electrons and active oxygen species at anodic interface sites, leading to oxidation of the hydrocarbon to CO2. On the other hand, O 2 reacts with protons and electrons to form H2O at cathodic interface sites. As a consequence, local electrochemical cells are formed at the interfaces, and undergo self-discharge. It was shown that the mixed catalyst had a high turnover frequency for Pt, yielding high catalytic activity for Pt contents of as low as 0.1 wt% and an initiation temperature for hydrocarbon oxidation of 150 °C. © 2010 Elsevier Inc.

DOI： 10.1016/j.jcat.2010.04.022

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Journal of Catalysis  

The intermediate-temperature and low-pressure production of methanol from methane in a one-pass process was investigated using a micro- or nanosized electrocatalyst system. The powdered catalyst was prepared by mixing proton-conducting Sn0.9In0.1P2O7 particles with high-activity Pd-Au-Cu/C particles to provide numerous electrolyte-electrode interfaces as reaction sites for methane oxidation. For a feed mixture of H2O, O2, and methane, a local electrochemical cell can be formed at the electrode-electrolyte interface: H2O → 1/2O2 + 2H+ + 2e- at the anode site; O2 + CH4 + 2H+ + 2e- → CH3OH + H2O at the cathode site. In addition, the electrode also functions as a lead wire that short-circuits the cell. Therefore, the overall reaction can be expected to be CH4 + 1/2O2 → CH3OH. The series of reactions successfully resulted in reduction in the temperature for initiation of methane oxidation to 250 °C and increased the methanol yield while maintaining a very high selectivity toward methanol for temperatures up to 400 °C. © 2010 Elsevier Inc. All rights reserved.

DOI： 10.1016/j.jcat.2010.01.011

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Sensors and Actuators, B: Chemical  

The carbon oxidation activity and sensing performance of an alumina substrate-supported sensor comprised of Sn0.9In0.1P2O7 as a proton conductor and Pt as an electrocatalyst were investigated. Electrochemically formed active oxygen species exhibited high activity for carbon oxidation, where the current efficiency was estimated from the four-electron reaction (C + 2H2O → CO2 + 4H+ + 4e-) and reached approximately 90%. An operating temperature of 225 °C was found to be the most effective to achieve the highest possible electrochemical carbon oxidation and the lowest possible non-electrochemical carbon oxidation. When carbon introduced to the Sn0.9In0.1P2O7-Pt interface was oxidized by active oxygen, a large potential jump was observed due to a significant increase in the polarization resistance, which was strongly dependent on the carbon content in the working electrode. Two types of carbon sensors, amperometric and potentiometric, were tested in a feed mixture of 3 vol% water vapor and 10 vol% O2. In the case of the amperometric sensor, the current increased linearly with increasing carbon content, which enabled the determination of a wide range of carbon content from the current signal. In the case of the potentiometric sensor, a threshold quantity of carbon could be recognized by selection of the current and subsequent monitoring of the sudden potential increase. © 2010 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.snb.2010.01.030

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)  

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Authorship：Lead author   Language：Japanese  

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Electrochemical and Solid-State Letters  

A high temperature and low humidity composite membrane consisting of Sn0.95 Al0.05 P2 O7 and sulfonated polystyrene- b -poly(ethylene/butylene)- b -polystyrene (sSEBS) as inorganic and organic materials, respectively, was prepared and characterized. A homogeneous distribution of the Sn0.95 Al0.05 P2 O 7 particles in the matrix was accomplished in the thickness range of 25-80 μm, providing an elongation at break above 400%, which is approximately two times higher than that for Nafion. Moreover, moderate proton conductivities of sSEBS improved proton transfer between the Sn0.95 Al 0.05 P2 O7 particles in the matrix, resulting in a proton conductivity of approximately 0.01 S cm-1 at 130°C without any humidification, which is 3 or more orders of magnitude higher than that for Nafion under the same conditions. © 2009 The Electrochemical Society.

DOI： 10.1149/1.3267848

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Electrochemical and Solid-State Letters  

Proton conduction is reported in partially proton-exchanged WP2 O7 at intermediate temperatures. Electrochemical measurements demonstrated that proton conduction occurs in this material. Proton magic angle spinning nuclear magnetic resonance and Fourier transform IR analyses revealed that the ion-exchanged protons interact with the lattice oxide ions in WP 2 O7 to form hydrogen bonds. The H/D isotope effect suggests that proton conduction in this material is based on the hopping mechanism. Consequently, the electrical conductivity of this material reached 1.1× 10-3 S cm-1 at 250°C and 1.7× 10 -2 S cm-1 at 500°C. © 2010 The Electrochemical Society.

DOI： 10.1149/1.3485076

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Journal of Materials Chemistry  

Intermediate-temperature fuel cells have received much recent attention as next generation energy sources. In particular, current efforts are devoted to developing proton conductors that operate at 120°C or more and at low relative humidity. Proton conduction in several metal pyrophosphates (MP 2O7, M = Sn, Ti, Si, Ge, Ce, and Zr) that have the potential to meet the demands for intermediate-temperature fuel cell applications are reviewed with an emphasis on the material aspects. © 2010 The Royal Society of Chemistry.

DOI： 10.1039/b924188d

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Sensors and Actuators, B: Chemical  

The formation of active oxygen by electrochemical oxidation of H2O vapor, coupled with carbon detection using those oxygen species, has been investigated by utilizing Sn0.9In0.1P2O7 as a proton conductor and Pt as an electrocatalyst. The H2O vapor was dissociated into protons and electrons at a Pt-carbon working electrode, which produced active oxygen on the carbon surface. This oxygen species showed high activity for carbon oxidation at temperatures of 50 °C or higher, where CO2 formation increased with temperature and reached the theoretical value calculated from the four-electron reaction (C + H2O → CO2 + 4H+ + 4e-) at 200 °C. When the formation rate of active oxygen was greater than the oxidation rate of carbon at the working electrode, the electrode potential increased rapidly due to a significant increase in polarization resistance. The timing of the potential jump was strongly dependent on both the carbon content in the working electrode and the current to the working electrode, which provides information on the quantity of carbon. In addition, little interference was encountered in sensing for carbon at 1000 ppm CO and 1000 ppm C3H8 in the sample gas. The high selectivity toward carbon was based on different mechanisms for CO and C3H8; almost all of the CO was catalytically oxidized to CO2 before reacting with active oxygen, while C3H8 experienced little reaction with active oxygen. These results demonstrate that the present sensor sensitively and selectively detects carbon while self-regenerating. © 2009 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.snb.2009.04.044

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Authorship：Lead author   Language：Japanese  

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Electrochemical and Solid-State Letters  

Nanosized proton-conducting Sn0.95 In0.05 P2 O7 ionomers were grown on carbon supports by the coprecipitation of tin and indium chlorides with excess ammonia water and subsequent solid-state reaction with phosphoric acid. The resulting homogeneous networks of Sn0.95 In0.05 P2 O7 ionomers enhanced the activity of a Pt catalyst for the oxygen reduction reaction in the temperature range of 150-250°C. In addition, the Pt catalyst showed high corrosion resistance in the cathode environment while maintaining high performance levels. A comparison of the cathode performance between Sn0.95 In0.05 P2 O7 and H3 P O4 ionomers further demonstrated that the Sn0.95 In0.05 P2 O7 nanoparticles are promising candidates for cathode ionomer materials at high temperatures. © 2008 The Electrochemical Society.

DOI： 10.1149/1.3006328

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Journal of the Electrochemical Society  

Mg-, In-, and Al-doped SnP2 O7 were synthesized, and their potential as electrolytes for fuel cells was evaluated in terms of their performance and durability. The overall conductivity of Mg-doped SnP2 O7 increased with increasing Mg2+ content and reached a maximum at 10 mol %. However, this was smaller than that obtained for doping with 10 mol % In3+ and 5 mol % Al3+, especially at temperatures below 300°C. This result was interpreted to be a consequence of lower proton mobility rather than of smaller proton concentration in Mg-doped SnP2 O7, probably due to the electrostatic restriction by Mg2+ against proton transport. Moreover, to investigate the influence of the Mg2+ doping on the fuel-cell properties, fuel-cell tests were conducted using Sn0.9 Mg0.1 P2 O7, Sn0.9 In0.1 P2 O7, and Sn0.95 Al0.05 P2 O7 as electrolytes at a temperature of 150°C. Compared with Sn0.9 In0.1 P2 O7 and Sn0.95 Al0.05 P2 O7 cells, the Sn0.9 Mg0.1 P2 O7 cell showed a somewhat higher Ohmic resistance but exhibited a comparable polarization resistance, which is the main component of the total electrical resistance. More importantly, the Mg2+ doping led to an improved stability of the Pt catalyst and carbon support at high potentials. This beneficial effect was attributed to a large reduction in the acidity of SnP2 O7 resulting from the basicity of MgO. © 2009 The Electrochemical Society.

DOI： 10.1149/1.3123219

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Electrochemical and Solid-State Letters  

We demonstrate an approach to impart both proton conduction and solid acidity to the surface of yttria-stabilized zirconia (YSZ). By reacting a YSZ substrate with liquid H3PO4 at 500°C, a thin Zr 1-xYx P2O7 film is grown on the substrate, which shows proton conductivity dependence on humidity and strong acid sites interacting with basic ammonia gas. This technique can be applied to gas sensor devices, yielding a remarkably sensitive and selective response to low concentrations (parts per million) of ammonia. Another important achievement of this technique is the realization of sensing properties in spite of using a conventional Pt electrode. © 2009 The Electrochemical Society.

DOI： 10.1149/1.3156836

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Fuel Cells  

The feasibility of applying single-chamber solid oxide fuel cells (SC-SOFCs) to power generators for exhaust energy recovery was investigated using both model and actual exhaust gases. In the experiments with model exhaust gases, a single cell, Ni-Ce0.8Sm0.2O1.9/YSZ/ La0.8Sr0.2MnO3, was operated in a mixture of gases containing ppm levels of CH4, C2H6, C3H3, C4H10and O2. The cell performance was considerably affected by the molar ratio of total hydrocarbons to O2, the operating temperature and the gas flow rate. The optimal operating conditions of the SC-SOFC were found to be similar to those found in actual exhaust from gasoline engines. Thermal and mechanical loading performance tests demonstrated high tolerance towards thermal cycling and breakage of the electrolyte. Performance tests with and without a gas separator suggested that there is no requirement for a gas separator in an actual exhaust. In the experiments with actual exhaust gases, a 12-cell stack was installed to a 250-cm3 engine. The open circuit voltages (OCVs) were between 5 and 8 V and independent of the number of revolutions, but were lower than the values expected from the model exhaust results. This was considered to be due to the deviation of the actual exhaust gases from the model gases. Nevertheless, the stack performance was reproducible and stable in the range from 1,500 to 5,500 rpm. The resultant peak power reached above 1 W at 4,500 rpm. © 2008 WILEY-VCH Verlag GmbH & Co. KGaA.

DOI： 10.1002/fuce.200800017

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Solid State Ionics  

An electrochemical cell using an In3+-doped SnP2O7 proton conductor as the electrolyte exhibited comparable NO reduction and sensing properties at around 250 °C. NO was reduced to N2 most effectively when using a PtRhBa/C cathode by applying current to the cell. High electrocatalytic activity was maintained even in the presence of CO2 and H2O. PtRhBa/C was also found to be the most effective electrode material for NOx sensing. The sensor exhibited electromotive force (EMF) response towards the positive direction with increasing NO and NO2 concentrations. The polarization curves of NO/NO2 and water vapor indicated that the sensing mechanism is based on the mixed potential. The effects of added Rh and Ba to the Pt/C electrode were explained in terms of selective reduction and adsorption of NO/NO2 over the electrode surface, respectively. © 2008 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.ssi.2008.03.033

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Solid State Ionics  

Pt-free fuel cells were investigated using a proton-conducting Sn0.9In0.1P2O7 electrolyte at intermediate temperatures between 150 and 300 °C. Transition metal oxides were applied as non Pt cathode catalysts. A ZrO2/C catalyst showed the highest catalytic activity for the oxygen reduction reaction among the metal oxides tested. The catalytic activity of ZrO2/C was further improved by optimizing the heat-treatment temperature for ZrO2/C. XRD measurements revealed that the high catalytic activity was attributed to the crystal structure of tetragonal ZrO2. Finally, we evaluated performance of a Pt-free fuel cell using the ZrO2/C cathode with a Mo2C-ZrO2/C anode that shows Pt-like behavior in reducing atmospheres. Reasonable performance was achieved by operating the Pt-free fuel cell at intermediate temperatures above 200 °C. © 2008 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.ssi.2007.12.090

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Angewandte Chemie - International Edition  

Low temperature, high voltage! Direct oxidation of hydrocarbon fuels, including methane, ethane, propane, and butane, occurs over Pt-free anodes in a proton-conducting fuel cell in the temperature range 100-300°C. A Mo 2C-ZrO2/C anode (30 mg Mo2C-ZrO2 per cm2) yields power densities equal to those obtained from Pt/C anodes (1-7 mg Pt per cm2) and generates higher open-circuit voltages than the Pt/C anodes. (Figure Presented) © 2008 Wiley-VCH Verlag GmbH & Co. KGaA.

DOI： 10.1002/anie.200801667

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Electrochemical and Solid-State Letters  

Heat engines emit huge amounts of exhaust which contain considerable quantities of heat and chemical energies. An increasing public awareness of global warming and oil depletion has required the development of innovative methods of recovering energy from such exhaust. A promising approach is to produce electricity from unburned fuel by using a fuel cell system. The exhaust includes cracked-light hydrocarbons, offering the possibility of applying this system to a power generator. Solid oxide fuel cells (SOFCs) can work at elevated temperatures but have poor thermal and mechanical shock resistance. In this study, we address this problem by operating the fuel cell system in a single-chamber mode, wherein no separation between fuel and oxidant gases is required. This operation provides high tolerance toward thermal cycling and breakage of the electrolyte. As a result, a twelve-cell stack exhibits stable and high performance in the exhaust from a motorcycle. © 2007 The Electrochemical Society.

DOI： 10.1149/1.2824502

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Angewandte Chemie - International Edition  

(Chemical Equation Presented) Fuel for thought? The direct oxidation of methane to methanol occurs at atmospheric pressure between 50 and 250°C in a fuel-cell-type reactor (see picture). The efficiency of the electrochemical activation of oxygen is higher than that for the catalytic activation of oxygen. © 2008 Wiley-VCH Verlag GmbH & Co. KGaA.

DOI： 10.1002/anie.200703928

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Journal of the Electrochemical Society  

Direct dimethyl ether fuel cells (DDMEFCs) were investigated using proton-conducting Sn0.9 In0.1 P2 O7 as an electrolyte at intermediate temperatures between 150 and 300°C. Fuel cell operation at intermediate temperatures allowed a PtC anode to achieve excellent CO tolerance and high catalytic activity for the anode reaction of DME. The catalytic activity of the PtC anode was further improved by the addition of Ru to Pt, especially at elevated temperatures. The anodic overpotential and anode product measurements revealed that the H2 produced by the reforming reaction of DME was electrochemically oxidized at the PtRuC anode, which proceeded in parallel with the direct oxidation reaction of DME. As a result, DDMEFCs with the PtRuC anode achieved a peak power density of 31, 52, and 78 mW cm-2 at 200, 250, and 300°C, respectively. © 2007 The Electrochemical Society.

DOI： 10.1149/1.2803509

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Electrochemical and Solid-State Letters  

A BaCe1-x Gdx O3-α (BCG) layer was grown between Ce0.9 Gd0.1 O1.95 (GDC) layers. This was accomplished by a solid-state reaction of a BaO layer with the GDC layer. In the multilayered GDC/BCG/GDC electrolyte film, all layers showed dense and homogeneous junction structure. When a hydrogen-air fuel cell with the multilayered electrolyte cell was tested at 550-800°C, the BCG layer could partially block the electronic current through the cell. The resulting open-circuit voltage and power density were increased by a maximum of 127 mV and 202 mW cm-2, respectively, compared with those for a single-layered GDC electrolyte cell under the same conditions. © 2008 The Electrochemical Society.

DOI： 10.1149/1.2865507

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Electrochemical and Solid-State Letters  

The present study proposed a scheme for the reaction between NOx and C3 H6 in the presence of excess O2 over a proton-conducting Sn0.9 In0.1 P2 O7 -supported PtRh catalyst. C3 H6 dissociated to protons and electrons at an anodic site of the PtRh catalyst, causing a negative potential. NOx reacted with protons and electrons to form N2 and H2 O at a cathodic site of the PtRh catalyst, resulting in a positive potential. As a result, an electrochemical local cell was formed at the PtRh Sn0.9 In0.1 P2 O7, followed by self-discharge. This series of reactions could be clearly distinguished from conventional catalytic reduction of NOx by C3 H6. © 2008 The Electrochemical Society. All rights reserved.

DOI： 10.1149/1.2966293

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Electrochemical and Solid-State Letters  

Proton-conducting composite membranes were fabricated by blending Sn0.95 Al0.05 P2 O7 having an excess of phosphates with polybenzimidazole (PBI) and polytetrafluoroethylene (PTFE). The addition of PBI to Sn0.95 Al0.05 P2 O7 - Px Oy powder stabilized the conductivity of the composite, providing higher conductivities than those of stoichiometric Sn0.95 Al0.05 P2 O7. The addition of PTFE to Sn0.95 Al0.05 P2 O7 - Px Oy -PBI powder reduced the conductivity but increased the tensile strength. The resulting composite membrane exhibited a conductivity of 0.04 S cm-1 at 200°C and a tensile strength of 2.30 MPa. Moreover, a fuel cell made with this composite membrane yielded high power densities exceeding 200 mW cm-2 above 100°C and good durability under unhumidified conditions. © 2008 The Electrochemical Society.

DOI： 10.1149/1.2897758

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Journal of Catalysis  

The selective catalytic reduction (SCR) of NOx by H2 was studied using proton-conducting Sn0.9In0.1P2O7 as a catalyst support at 50-350 °C. When a mixture of 800 ppm NO, 1400-8400 ppm H2, and 5% O2 in Ar was introduced to the Pt/C working electrode, NOx was reduced to N2 with N2 selectivity values > 80 %. The reaction mechanism was shown to be based on a mixed potential at the Pt/C working electrode. This mechanism was also applicable to a Sn0.9In0.1P2O7-supported Pt catalyst. H2 SCR over the Pt/Sn0.9In0.1P2O7 catalyst was characterized by a wide operating temperature window (50-350 °C) and remarkable N2 selectivity values (> 80 %). Catalyst performance could be further improved by the addition of Rh to Pt, in which NOx conversion was a maximum 1.4 times higher than that over the Pt/Sn0.9In0.1P2O7 catalyst and N2 selectivity was increased to > 89 % at all temperatures tested. © 2007 Elsevier Inc. All rights reserved.

DOI： 10.1016/j.jcat.2007.02.001

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Solid State Ionics  

Solid oxide fuel cells (SOFCs) have received much recent attention as next generation alternative energy sources. In particular, current efforts are devoted to reducing SOFC costs by downsizing fuel cell systems and lowering the operating temperature. Single-chamber SOFCs (SC-SOFCs) have the potential of meeting the demands. This type of fuel cell consists of only one gas chamber, wherein the anode and cathode are exposed to the same mixture of fuel and oxidant gas. This simplified design offers the possibility of reducing stack components and eliminating the need for sealing. Furthermore, since the principle of operation in the mixture is based on exothermic partial oxidation of the fuel that evolves a large amount of reaction heat, the cell temperature can be efficiently increased, enhancing the ion conductivity of the electrolyte and the catalytic activity of the electrodes. This paper reviews the current status of SC-SOFCs with principal emphasis on the materials aspect. In addition, the benefits and limitations of SC-SOFCs are discussed based on the cell design, performance, and energy efficiency. © 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.ssi.2006.10.014

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Authorship：Lead author   Language：Japanese  

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Journal of the Electrochemical Society  

Anode performance of non-Pt catalysts for hydrogen oxidation was investigated in intermediate-temperature proton exchange membrane fuel cells. Molybdenum carbide (Mo2 C) showed the highest catalytic activity among the transition metal carbides tested. Furthermore, the catalytic activity of Mo2 C was significantly improved by the addition of ZrO2 to the anode. Transmission electron microscopy and X-ray diffraction measurements revealed that Mo2 C was more highly dispersed in the Mo2 C- ZrO2 C than in the Mo2 CC, suggesting that the particle growth of Mo2 C was suppressed by the addition of ZrO2. We also tested the performance of a fuel cell using Mo2 C- ZrO2 C and Sn0.9 In0.1 P2 O7 as the anode and electrolyte materials, respectively, between 150 and 300°C. At 250°C or higher, the Mo2 C- ZrO2 C anode showed a cell performance comparable to that of the PtC anode. However, cell performance was strongly dependent on the operating temperature, reflecting that the catalytic activity of Mo2 C- ZrO2 was greatly lowered by the decrease in operating temperature. Thus it was concluded that the Mo2 C- ZrO2 catalyst is a promising alternative anode material to Pt, especially at intermediate temperatures. © 2006 The Electrochemical Society.

DOI： 10.1149/1.2382268

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Electrochemical and Solid-State Letters  

Sodium phosphate additives and mixed electrolytes of Li (C2 F5 SO2) 2 N (LiBETI) and LiPF6 were examined to improve cycle performances of Li1.04 Mn1.96 O4 /graphite cells at high temperatures. The cycle performance of those cells exceeded 80% at 100 cycles at 55°C in an optimum combination of a 0.975 M LiBETI and 0.025 M LiPF6 /ethylene carbonate (EC):dimethylcarbonate (DMC) (1:2) electrolyte solution containing 5% of Na4 P2 O7 or 5% of Na5 P3 O10 additive. Such a cycle performance is considered to fulfill the requirement for practical use. © 2007 The Electrochemical Society.

DOI： 10.1149/1.2784141

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Journal of the Electrochemical Society  

Al3+ -doped Sn P2 O7 proton conductors were prepared by controlling the initial composition of the reactants [Sn O2, Al (OH)3, and H3 P O4]. Sn1-x Alx Py Oz with y<2 displayed conductivities approximately two orders of magnitude lower than Sn1-x Alx P2 O7, while those of Sn1-x Alx Py Oz with y>2 exhibited conductivities at a maximum of 1.99 times higher. However, because the conductivity values of Sn1-x Alx Py Oz with y>2 were not stable, the optimal value of y in Sn1-x Alx Py Oz was determined to be 2. Partial substitution of Al3+ for Sn4+ in Sn1-x Alx P2 O7 led to an increase in the conductivity up until x=0.05. As a result, the conductivity reached 0.045 S cm-1 at 100°C, 0.15 S cm-1 at 200°C, and 0.19 S cm-1 at 300°C when the x and y values were 0.05 and 2, respectively. A hydrogen concentration cell with this material demonstrated that the ionic transport number was ∼1, and a fuel cell using this material demonstrated that the dc conductivity was comparable to the ac conductivity. © 2007 The Electrochemical Society.

DOI： 10.1149/1.2789296

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Journal of the Electrochemical Society  

A potentiometric solid-state gas sensor was fabricated using a proton-conducting Sn0.9 In0.1 P2 O7 electrolyte with an active PtC working electrode in order to study its sensing properties for small quantities (100 ppm 3%) of H2 in air at room temperature. The sensor showed electromotive force (emf) response in the negative direction to changes in the H2 concentration. Furthermore, the emf value varied linearly with the logarithm of the H2 concentration, while it was minimally affected by the water-vapor concentration. The sensing mechanism was shown to be based on the mixed potential at the working electrode through measurements of the polarization curves of H2 and air. The Sn0.9 In0.1 P2 O7 electrolyte was also applied in two single-chamber H2 sensors, wherein PtC and carbon were used as active and inactive electrodes, respectively; these electrodes were attached on the opposite surfaces or on the same surface of the electrolyte. Both single-chamber sensors could exhibit comparable H2 sensitivities, compared to the dual-chamber sensor. © 2007 The Electrochemical Society.

DOI： 10.1149/1.2713702

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Journal of the Electrochemical Society  

An anhydrous proton conductor, 10 mol % In3+ -doped SnP2 O7 (Sn0.9 In0.1 P2 O7), was composed by 1,8-bis(triethoxysilyl)octane (TES-Oct) and 3-(trihydroxysilyl)-1-propanesulfonic acid ((THS)Pro- SO3 H) and was characterized by structural and electrochemical analysis. The composite membrane with 90 wt % Sn0.9 In0.1 P2 O7 showed high proton conductivities of 0.04 S cm-1 or more between 150 and 200°C in unhumidified air. The packing of the Sn0.9 In0.1 P2 O7 particles in the matrix was relatively uniform, with no formation of pinholes observed. Fuel cell tests verified that the open-circuit voltage was maintained at a constant value of ∼970 mV regardless of the electrolyte thickness (60-200 μm), while the Ohmic resistance was decreased to 0.24 cm2 by reducing the electrolyte thickness to 60 μm. The peak power densities achieved with unhumidified H2 and air were 109 mW cm-2 at 100°C, 149 mW cm-2 at 150°C, and 187 mW cm-2 at 200°C. Furthermore, fuel cell performance was improved by hot-pressing an intermediate layer consisting of Sn0.9 In0.1 P2 O7, PtC, TES-Oct, and (THS)Pro- SO3 H between the electrolyte and cathode. © 2006 The Electrochemical Society.

DOI： 10.1149/1.2388737

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Journal of the Electrochemical Society  

An anode-supported single-chamber solid oxide fuel cell (SC-SOFC), consisting of a Ce0.9 Gd0.1 O1.9 electrolyte, a Ni- Ce0.8 Sm0.2 O1.8 (SDC) cermet anode, and a Sm0.5 Sr0.5 Co O3 cathode, was operated in a mixture feed of dimethyl ether (DME), ethanol or butane, and air at a furnace temperature of 300°C. This SC-SOFC showed comparatively poor performance for DME and ethanol fuels when compared to the performance for butane fuel, resulting from the relatively small difference in catalytic activity for DME and ethanol oxidation between the anode and the cathode. An effective improvement was achieved by attaching Ru/SDC/Ni and CuZnAl catalyst layers for DME and ethanol, respectively, on the anode surface. As a result, peak power densities of 64 and 117 mW cm-2 were obtained for DME and ethanol, respectively. © 2007 The Electrochemical Society.

DOI： 10.1149/1.2747326

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Solid State Ionics  

The operation of a solid oxide fuel cell (SOFC) based on BaCe0.8Y0.2O3-α (BCY20) at 800 °C was studied without using an anode material. A porous, Ce-rich phase with a fluorite structure was formed at a depth of approximately 10 μm from the BCY20 surface by heat treatment at 1700 °C. This was due to the vaporization of BaO from the BCY20 surface. This treatment improved the cell performance and chemical stability to CO2 because the Ce-rich phase functioned as an electrically conducting and protective layer. The heat-treated BCY20 also had better chemical and redox stabilities over a Ni-Ce0.8Sm0.2O1.9 (SDC) cermet anode attached to the SDC electrolyte. The cell with the heat-treated BCY20 operated well on unhumidified methane, ethane, propane, and butane without carbon deposition, while the cell with the Ni-SDC cermet anode degraded within a few hours. Moreover, the BCY20 showed higher tolerance to 10 ppm H2S and stability over 20 times redox cycling in comparison to the Ni-SDC cermet anode. © 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.ssi.2006.08.031

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：ECS Transactions  

Proton exchange membrane fuel cells (PEMFCs) are among the most promising power sources for vehicular and residential applications because of their clean and efficient energy conversion. However, these fuel cells require expensive Pt-based electrodes, which raise the cost of fuel-cell systems considerably. Here, we propose an approach to solving this problem by combining a molybdenum carbide (Mo2C) catalyst with an In3+-doped SnP 2O7 electrolyte. The resulting fuel cell can operate in the temperature range of 150 to 300°C, providing the high catalytic activity of Mo2C for electrochemical hydrogen oxidation, which is comparable to that of a Pt anode catalyst. Another important advantage of this fuel cell is that the Mo2C anode catalyst showed perfect tolerance to 10%CO. copyright The Electrochemical Society.

DOI： 10.1149/1.2356166

Scopus

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Electrochemical and Solid-State Letters  

We report proton conduction in In3+ -doped Sn P2 O7 in the temperature range from 100 to 300°C, and the performance of a H2 -air fuel cell using this material as the electrolyte. The proton conductivity of In3+ -doped Sn P2 O7 was more than 10-1 S cm-1 between 125 and 300°C, and a conductivity value of 1.95× 10-1 S cm-1 was achieved at 250°C. The resulting fuel cell exhibited a reasonable power density of 264 mW cm-2 at 250°C (electrolyte thickness=0.35 mm), together with perfect tolerance toward 10% CO and good thermal stability in unhumidified conditions. © 2006 The Electrochemical Society. All rights reserved.

DOI： 10.1149/1.2159298

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Journal of the Electrochemical Society  

Multilayered Ce0.9 Gd0.1 O1.95 Ba Ce0.8 Y0.2 O3-α Ce0.9 Gd0.1 O1.95 (GDCBCYGDC) electrolytes were prepared by tape casting on a Ni- Ce0.8 Sm0.2 O1.9 anode support. The overall electrolyte thickness ranged from 30 to 35 μm, including a 3 μm thick BCY layer. When the multilayered electrolyte cell was tested with hydrogen at the anode and air at the cathode in the temperature range of 500-700°C, it yielded open-circuit voltages (OCVs) of 846-1024 mV, which were higher than the OCVs of 753-933 mV obtained for a single-layered GDC electrolyte cell under the same conditions. The corresponding peak power densities reached 273, 731, and 1025 mW cm-2 at 500, 600, and 700°C, respectively. The multilayered electrolyte cell could also be applied to direct methane solid oxide fuel cell (SOFC) and single-chamber SOFC operating in a mixture of methane and air. These SOFCs yielded OCVs of 880-950 mV and reasonable power densities without coking. © 2006 The Electrochemical Society.

DOI： 10.1149/1.2186184

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Electrochemical and Solid-State Letters  

In 3+-doped SnP 2O 7 was used as the electrolyte in an electrochemical cell for the reduction of NO between 150 and 300°C in the presence of excess O 2. NO was reduced to N 2 at a Pt/C cathode when current was applied to the cell. The electrocatalytic activity of the cathode for the reduction of NO was shown to be highest at 250°C. The addition of Ba species (an oxide/carbonate mixture) to the cathode further promoted the reduction of NO by adsorbing NO more selectively than O 2 on the surface. A resulting current efficiency of 5.81% was achieved in a 2% O 2 atmosphere. © 2005 The Electrochemical Society. All rights reserved.

DOI： 10.1149/1.2149213

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Electrochemical and Solid-State Letters  

A potentiometric NOx sensor using a proton-conducting Sn0.9 In0.1 P2 O7 electrolyte with a PtRhC working electrode was fabricated to study sensing properties for NO and N O2 at intermediate temperatures. The sensor showed electromotive force (emf) responses to changes in NO and N O2 concentrations. Interestingly, the emf values for both NO and N O2 increased in the positive direction with increasing gas concentration. The sensing mechanism was shown to be based on a mixed potential at the working electrode through measurements of the polarization curves of NO or N O2 and water vapor. © 2006 The Electrochemical Society.

DOI： 10.1149/1.2193073

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Journal of the Electrochemical Society  

Performance of a fuel cell using Sn0.9 In0.1 P2 O7 as the electrolyte was evaluated in the temperature range of 150-300°C under unhumidified conditions. The IR drop and electrode overpotential of the cell were measured separately by the current interruption method. The dc conductivity values of the electrolyte between 150 and 300°C, estimated from the IR drop, were comparable to the ac conductivity values (1.48× 10-1 -1.95× 10-1 S cm-1) of the electrolyte. The cell performance was improved by forming an intermediate layer consisting of Sn0.9 In0.1 P2 O7 and PtC catalyst powders at the interface between the electrolyte and cathode, which significantly reduced the cathode polarization. As a result, the peak power density reached 264 mW cm-2 at 250°C using the 0.35-mm -thick electrolyte. The present fuel cell also showed high stability at low relative humidities (p H2 O ≈0.0075 atm) and 10% CO concentration. © 2006 The Electrochemical Society. All rights reserved.

DOI： 10.1149/1.2183927

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：ECS Transactions  

A proton conducting, 10 mol% In3+-doped SnP2O 7 (Sn0.9In0.1 P2O7) was characterized by thermogravimetric analysis (TGA), transmission electron microscope (TEM) measurement, and electrochemical techniques. We prepared Sn0.9In0.1P2=x07±x samples with various P/(Sn+In) molar ratios from 1.7 to 2.6 through the control of the amount of phosphoric acid at the preparation process in order to examine electrochemical properties and thermal stabilities. Sn0.9In 0.1P2O7 with a stoichiometric P/(Sn+In) molar ratio of 2.0 showed a proton conductivity of about 0.19 S cm-1 at 250°C under unhumidified conditions. When the P/(Sn+In) molar ratios were over 2.0, the formation of amorphous layer composed of phosphorus compounds were observed over the surface of Sn0.9In0.1P 2O7 particles. The proton conductivity slightly increased with increasing the P/(Sn+In) molar ratios from 2.0 to 2.6. It is considered that the amorphous layer enhanced the proton conductivity by surface conduction. On the other hand, the thermal stability of this amorphous layer during heating-cooling cycle was not enough high to apply to electrochemical devises. As a result, it is important to prepare Sn0.9In0.1P 2O7 with the P/(Sn+In) molar ratio of 2.0 to achieve both sufficient proton conductivity and high thermal stability. Copyright The Electrochemical Society.

DOI： 10.1149/1.2408942

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Journal of the Electrochemical Society  

SnP2 O7 -based proton conductors were characterized by Fourier transform infrared spectroscopy (FTIR), temperature-programmed desorption (TPD), X-ray diffraction (XRD), and electrochemical techniques. Undoped SnP2 O7 showed overall conductivities greater than 10-2 S cm-1 in the temperature range of 75-300°C. The proton transport numbers of this material at 250°C under various conditions were estimated, based on the ratio of the electromotive force of the galvanic cells to the theoretical values, to be 0.97-0.99 in humidified H2 and 0.89-0.92 under fuel cell conditions. Partial substitution of In3+ for Sn4+ led to an increase in the proton conductivity (from 5.56× 10-2 to 1.95× 10-1 S cm-1 at 250°C, for example). FTIR and TPD measurements revealed that the effects of doping on the proton conductivity could be attributed to an increase in the proton concentration in the bulk Sn1-x Inx P2 O7. The deficiency of P2 O7 ions in the Sn1-x Inx P2 O7 bulk decreased the proton conductivity by several orders of magnitude, which was explained as due to a decrease in the proton mobility rather than the proton concentration. The mechanism of proton incorporation and conduction is examined and discussed in detail. © 2006 The Electrochemical Society. All rights reserved.

DOI： 10.1149/1.2210669

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Solid State Ionics  

Sm3+-doped ceria (SDC) electrolytes growing various BaCe 1-xSmxO3-α (BCS) layers over the electrolyte surface were investigated in order to develop high-performance solid oxide fuel cells in the temperature range of 600-900°C. The BCS layers were grown by a solid-state reaction of the electrolyte substrate and a BaO film spin-coated previously over the substrate surface under different preparation conditions. The thickness of the layer was controlled with a precision of micrometer by the number of coats. The composition of the layer was optimized by the sintering temperature. As a result, a dense and microcrack-free BCS layer was formed over the electrolyte surface, and the junction between the electrolyte and layer was almost homogeneous. A hydrogen-air fuel cell with the improved electrolyte showed open-circuit voltages (OCVs) ranging from 857 (900°C) to 1002 mV (600°C). Furthermore, the peak power densities of this fuel cell were higher than those of a fuel cell with an uncoated SDC electrolyte. © 2004 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.ssi.2004.12.007

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Authorship：Lead author   Language：Japanese  

Authorship：Lead author   Language：Japanese  

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Electrochemical and Solid-State Letters  

Single-chamber solid oxide fuel cells (SOFCs) with an anode-supported Ce0.9Gd0.1O1.95 electrolyte were operated in a mixture of butane and air at furnace temperatures of 200-300°C. The electromotive force (emf) of the cell and the voltage drop were strongly influenced by the catalytic activity of the anode for the partial oxidation of butane. The promotion of hydrogen formation by the addition of Ru to the anode caused an increase in the emf and a reduction in the voltage drop. As a result, stable power densities of 44 and 176 mW cm-2 were obtained at 200 and 300°C, respectively. © 2004 The Electrochemical Society. All rights reserved.

DOI： 10.1149/1.1836120

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Electrochemical and Solid-State Letters  

Dual functions of BaCe0.8Y0.2O3-α, (BCY) as an electrolyte and as an anode were improved for solid oxide fuel cell (SOFC) applications. A porous Ce-rich phase with fluorite structure was formed with a depth of ∼10 μm from the BCY surface by vaporization of BaO from the BCY surface at 1700°C. The resulting BCY surface showed enough electronic conductivity to provide electrical collection and a high electrocatalytic activity for hydrogen oxidation. A hydrogen-air fuel cell with the BCY electrolyte exhibited reasonable performances without using an anode material between 750 and 950°C. © 2005 The Electrochemical Society. All rights reserved.

DOI： 10.1149/1.1928230

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Solid State Ionics  

A fuel cell-type microreader that generates both hydrogen and electrical power from dry butane around 700°C is presented for polymer-electrolyte fuel cell (PEFC) applications. To demonstrate this concept, solid-oxide fuel cells (SOFCs) with different Fe2O3-based anodes were fabricated, and their performances were evaluated. A Fe2O3/Cr 2O3 composite anode met this criterion the most; hydrogen was produced with increasing current density; CO2/CO concentration ratios in the outlet gases were more than 2; polarization resistances were about 1 Ω cm2; carbon deposition was much more suppressed with these anodes than with a Ni/SDC cermet anode. The resulting peak power density was 110 mW cm-2 by using a 0.25-mm-thick Ce0.9Gd 0.1O1.95 (GDC) electrolyte. The effect of Cr 2O3 added into the Fe2O3 anode was also discussed in detail. © 2004 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.ssi.2004.07.023

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Journal of Power Sources  

Two lithium manganese oxides, Li1.03Mn1.96O 4, with different surface areas of 3.55 and 0.68m2/g were prepared and their electrochemical properties were studied as positive electrodes for lithium ion batteries. Cycle performance tests gave capacity losses of 9 and 18% at 25°C, and 28 and 33% at 55°C for the samples with larger and smaller surface areas, respectively. The recovery of capacity losses have been found on the addition of the conductor after cycles. The defect of the conductivity between the active materials and the conductors was found mostly responsible for the capacity loss in the smaller surface sample at 25°C. Cycle performance tests in each region of the charge states divided into five regions show that larger capacity losses are observed in rather lower potential states. Storage performances show the largest capacity loss at 10 and 20% of SOC and the less capacity losses at both 0 and 50-100% of SOC in both of the samples. However, in every region, the capacity loss is much smaller in the larger surface sample than in the smaller surface sample. The maximum Mn dissolution is observed to occur at 100% of SOC (4.5V) and the next is found around 10-20% of SOC in either sample. © 2004 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jpowsour.2004.05.014

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)  

Web of Science

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Journal of Materials Science  

25 mol% Y3+-doped BaCeO3 (BCY25) showed an extremely low activation energy of 0.3 eV for proton conduction at the surface. The resulting overall conductivity at the surface reached 8.24 × 10 -3 S cm-1 at 400°C, which was 3, 8, and 28 times higher than those in the bulk of BCY25, 20 mol% Sm3+-doped ceria, and 8 mol% yttria-stabilized zirconia, respectively. Such fast proton conduction enabled an air/fuel (A/F) sensor using BCY25 as the solid electrolyte to work above 150°C for H2 and above 250°C for C2H 4. © 2004 Kluwer Academic Publishers.

DOI： 10.1023/B:JMSC.0000020015.80430.d8

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)  

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Solid State Ionics  

We proposed a new type of solid oxide fuel cell (SOFC) operating without using an anode material, where the anode was spontaneously formed by reduction of the electrolyte surface under reducing gas conditions. A BaCe 0.76Y0.20Pr0.04O3-α electrolyte most successfully met this criterion. This material showed high mixed protonic-electronic conduction, whereas the open circuit voltage (OCV) of the cell was slightly lower than the theoretical value. The resulting SOFC exhibited reasonable fuel cell performances together with a good stability to thermal and redox cyclings and high resistance to carbon deposition up to 800 °C for dry methane, ethane, and propane. © 2004 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.ssi.2004.01.024

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Electrochemical and Solid-State Letters  

Doped Bi-based oxides were investigated as potential anode materials for direct hydrocarbon solid oxide fuel cells (SOFCs) at intermediate temperatures. (Bi2O3)0.85(Ta2O5) 0.15 met this criterion most successfully. A fraction of Bi 2O3 in this material was reduced to BiO and Bi metal under fuel conditions, which yielded high conductivities (>1 S cm-1) based on oxide ions and electrons above 500°C. Carbon deposition was successfully prevented when butane was used as the fuel below 800°C. The catalytic activities for hydrocarbon oxidation were high enough to promote the complete oxidation of butane during cell operation. These abilities provided an enhanced anode performance with increasing temperature from 600 to 750°C, and the resulting polarization resistance reached 1.4 Ω cm2 at 750°C. © 2004 The Electrochemical Society. All rights reserved.

DOI： 10.1149/1.1667791

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Electrochemical and Solid-State Letters  

A method that can block off electronic current through a samaria-doped ceria (SDC, Ce0.8Sm0.2O1.9) electrolyte is proposed. A thin BaCeO3-based layer 12 μm thick was grown by a solid-state reaction of the electrolyte substrate and a BaO film deposited previously over the substrate surface at 1500°C. A homogeneous junction between the layer and the electrolyte was formed, thus allowing no delamination and cracking of the layer. Tolerance of this layer to CO2 was high enough to suppress decomposition into BaCO3 and CeO2. Open-circuit voltages of a hydrogen-air fuel cell with the coated SDC electrolyte were near 1 V or more in the range of 600-950°C. The resulting peak power density was higher than that of a fuel cell with an uncoated SDC electrolyte. © 2004 The Electrochemical Society.

DOI： 10.1149/1.1786231

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Key Engineering Materials  

The promotion of the direct electrochemical oxidation of hydrocarbons in a solid oxide fuel cell was investigated using a ceria-based electrolyte with different noble metals-containing anode at 600°C. The attempted approach toward this objective was to avoid interference from a large amount of steam and CO2 products, because they degrade the anode performance. Ru was an effective catalyst for removing these gases from the anode surface due to its high catalytic activity for the steam and CO2 reforming of hydrocarbons. This permitted a smooth access of the unreacted hydrocarbons to the three-phase boundary, thus resulting in a noticeably high anode performance. The resulting peak power density reached 750 mW cm-2 with dry methane, which was comparable to the peak power density of 769 mW cm -2 with wet hydrogen.

DOI： 10.4028/www.scientific.net/kem.269.151

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Electrochimica Acta  

A solid oxide fuel cell using a thin ceria-based electrolyte film with a Ru-catalyzed anode was directly operated on hydrocarbons, including methane, ethane, and propane, at 600 °C. The role of the Ru catalyst in the anode reaction was to promote the reforming reaction of the unreacted hydrocarbons by the produced steam and CO2, which avoided interference from steam and CO2 in the gas-phase diffusion of the fuels. The resulting peak power density reached 750 mW cm-2 with dry methane, which was comparable to the peak power density of 769 mW cm-2 with wet (2.9 vol.% H2O) hydrogen. More important was the fact that the cell performance was maintained at a high level regardless of the change in the methane utilization from 12 to 46% but was significantly reduced by increasing the hydrogen utilization from 13 to 42%. While the anodic reaction of hydrogen was controlled by the slow gas diffusion, the anodic reaction of methane was not subject to the onset of such a gas-diffusion process. © 2003 Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S0013-4686(03)00296-2

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)  

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Electrochemistry  

Resistor-type sensor devices using a samaria-doped ceria electrolyte with different working electrodes were fabricated for detecting carbon monoxide (CO) in reformed gases between 250 and 425°C. The electrochemical oxidation of H2 over a Pd working electrode was the most sensitive to a reversible poisoning by 50-4000 ppm CO in the presence of 50% hydrogen, 10% carbon dioxide, and 6% water vapor, which provided an increase in the electrode-reaction resistance at the electrode-electrolyte interface. The resulting sensor signal was strongly dependent on the CO concentration, where linear relationships between the signal and the logarithm of the CO concentration were obtained, especially below 1000 ppm with 90% response and 90% recovery times of about 20 seconds. An improvement in the CO-sensing properties of the present sensor device above 300°C was also carried out by the addition of Au to the Pd working electrode.

DOI： 10.5796/electrochemistry.71.398

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Authorship：Lead author   Language：Japanese  

Authorship：Lead author   Language：Japanese  

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Journal of the Electrochemical Society  

The performance of a solid oxide fuel cell (SOFC) with the configuration, H2, 3 wt % Pd-loaded FeO|25 mol % Y3+-doped BaCeO3 (BCY25)|Ba0.5Pr0.5CoO3, air, was studied between 350 and 600°C. The BCY25 electrolyte showed higher ion conductivities than 8 mol % yttria-stabilized zirconia (YSZ) below 800°C and 20 mol % Sm3+-doped ceria (SDC) below 600°C, thus having the smallest ohmic resistance loss during cell discharge below 600°C among the three electrolytes. The overpotentials of the Pd-loaded FeO anode and the Ba0.5Pr0.5CoO3 cathode at 600°C were 25 and 53 mV, respectively, at 200 mA cm-2, which were less than one-fourth those of a Pt electrode. The resulting peak power density was higher than those obtained for two SOFCs using the YSZ and SDC electrolytes with a Ni-SDC anode and a Sm0.5Sr0.5CoO3 cathode below 600°C.

DOI： 10.1149/1.1513983

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Electrochemical and Solid-State Letters  

The promotion of direct electrochemical oxidation of hydrocarbons in a solid oxide fuel cell was investigated using a ceria-based electrolyte with different noble metals-containing anode at 600°C. The objective was to avoid interference from a large amount of steam and CO2 being produced by discharging the cell, because these gases degrade the anode performance, especially at a high fuel utilization. Ru was an effective catalyst for removing these gases from the anode surface due to its high catalytic activity for the steam and CO2 reforming of hydrocarbons. The resulting peak power densities reached 750 mW cm-2 with dry methane, which was comparable to the peak power density of 769 mW cm-2 with wet (2.9 vol % H2O) hydrogen. The cell performance was maintained at a high level regardless of the change in methane utilization from 12 to 46% but was significantly reduced by increasing hydrogen utilization from 13 to 42%. The anodic reaction of hydrogen was controlled by the slow surface diffusion of hydrogen, while the anodic reaction of methane was not subject to the onset of such a gas-diffusion process.

DOI： 10.1149/1.1508551

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)  

Web of Science

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Sensors and Actuators, B: Chemical  

Solid oxide fuel cells (SOFCs) using Pd metal as the anode were fabricated for detection of CO in a flowing mixture of 0-4000 ppm CO, 50% H2, 10% CO2 and 6% H2O vapor between 300 and 400 °C. When 20 mol% Sm3+-doped CeO2 (SDC) was used as the electrolyte, the Pd anode was subjected to a large and reversible change in the anodic-reaction resistance with the CO concentration. This behavior brought about an almost linear relationship between the electromotive force (EMF) generated from the cell or the short-circuit current through the cell and the logarithm of the CO concentration. In both signals, the minimum detectable CO concentration was 50 ppm, and the 90% response and 90% recovery times were about 60 s. However, the EMF of the cell at a CO concentration of 0ppm significantly deviated from the theoretical value, which made it difficult to obtain reproducible data. In addition, the current signal of a few μA at a CO concentration of 4000 ppm was not large enough to monitor the CO concentration exactly. The improvement of these problems could be achieved by using 25 mol% Y3+-doped BaCeO3 (BCY25) with higher ionic conduction as the electrolyte: the EMF of the cell at a CO concentration of 0 ppm was near the theoretical value; the current signal reached 66 μA at a CO concentration of 4000 ppm. © 2002 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0925-4005(02)00068-0

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Electrochemical and Solid-State Letters  

A solid oxide fuel cell using a sumaria-doped ceria electrolyte with a Pd anode was fabricated for detecting carbon monoxide (CO) in reformed gases at 300°C. The CO concentration in a flowing mixture of 0-4000 ppm CO, 50% hydrogen, 10% carbon dioxide, and 6% water vapor was related to a decrease in both the electromotive force generated from the cell and the short-circuits current through the cell due to a reversible change in the anodic resistance with the CO concentration. In both signals, the minimum detectable concentration was 50 ppm, and the 90% response and 90% recovery times were as short as 20 s.

DOI： 10.1149/1.1432243

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Journal of the Electrochemical Society  

We propose a solid oxide fuel cell design based on a configuration of two electrodes on the same surface of the electrolyte in a flowing mixture of different hydrocarbons and air between 500 and 600°C. The ohmic resistance can be reduced without using a thin electrolyte film due to a significantly enhanced performance by the approach of the two electrodes to each other on the smooth electrolyte surface. The fuel cell performance, especially at reduced temperatures, is further improved by using a more reactive hydrocarbon fuel and a more catalytically active anode. The resulting power density reaches 122 mW cm-2 using 2 mm thicer electrolyte at 500°C. © 2002 The Electrochemical Society. All rights reserved.

DOI： 10.1149/1.1431573

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Journal of the Electrochemical Society  

Electrocatalytic oxidation of methane over anodes in single-chamber solid oxide fuel cells, 0-10 wt % Pd-30 wt % Ce0.8Sm0.2O1.9 (samaria-doped ceria, SDC)-Ni|SDC|Sm0.5Sr0.5CoO3, was studied in a mixture of methane and air between 450 and 550°C. The addition of a small amount of Pd (0.145 mg cm-2) to the anode significantly promoted the partial oxidation of methane by oxygen to form hydrogen and carbon monoxide, which resulted in electromotive forces of ca. 900 mV from the cell and extremely small electrode-reaction resistances of the anode. The peak power densities, when using a 0.15 mm thick SDC electrolyte, reached 644, 467, and 269 mW cm-2 at 550, 500, and 450°C, respectively. © 2002 The Electrochemical Society. All rights reserved.

DOI： 10.1149/1.1430226

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Authorship：Lead author   Language：Japanese  

Language：Japanese   Publishing type：Research paper (scientific journal)  

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Sensors and Actuators, B: Chemical  

The non-Nernstian behavior of zirconia-based oxygen sensors for 0-1000ppm C1-C5 hydrocarbons, carbon monoxide, and hydrogen was studied using various ion conductor-containing Pt electrodes in the presence of 10vol.% of oxygen at 600°C. The addition of a proton conductor, especially SrCe0.95Yb0.05O3-α (SCY), to the Pt electrode improved the sensitivity for the hydrocarbons over other reducing gases: -122mV for 1000ppm propene; -24mV for 1000ppm carbon monoxide; and -23mV for 1000ppm hydrogen. The EMF value of the cell was enhanced by the increasing carbon number of the hydrocarbons, the unsaturation of the C-C linkage, and the branching of the chain structure. A similar conclusion also applied to aromatic hydrocarbons: -81mV for 500ppm benzene; -96mV for 500ppm toluene; and -102mV for 500ppm p-xylene. This enhanced effect, as well as the addition effect of SCY, was discussed on the basis of the measurements of polarization curves for hydrocarbons and oxygen and the non-electrochemical oxidation of the hydrocarbons by oxygen. It was found that the added SCY did not inhibit the catalytic activities for the hydrocarbons, but decreased the cathodic reaction rate of oxygen, thus, shifting the mixed potential for the hydrocarbons to more negative values. © 2001 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0925-4005(01)00931-5

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Journal of Physical Chemistry B  

In our work, 25 mol % of Y3+-doped BaCeO3 (BCY25) showed an extremely low activation energy of 0.3 eV for proton conduction at the surface. The resulting overall conductivity at the surface reached 8.24 × 10-3 S cm-1 at 400 °C, which was 3, 8, and 28 times higher than conductivities in the bulk of BCY25, 20 mol % Sm3+-doped ceria, and 8 mol % yttriia-stabilized zirconia, respectively. A large H/D isotope effect strongly suggested that the enhanced proton conductivities were due to an advantageous jump of protons between adjacent oxide ions at the surface. Such fast proton conduction enabled an air/fuel sensor using BCY25 as the solid electrolyte to work at 200 °C or less.

DOI： 10.1021/jp0124342

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Language：Japanese   Publishing type：Research paper (scientific journal)  

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Journal of Physical Chemistry B  

Potentiometric sensors using different solid electrolytes, including proton, oxide-ion, and mixed proton and oxide-ion conductors, were fabricated to investigate a relationship between the mixed potential for C1-C4 hydrocarbons and ion conduction in the electrolyte in a mixture of hydrocarbons and oxygen at 600 °C. There was an increase in the mixed potential for the hydrocarbons with increasing proton conductivity or decreasing oxide-ion conductivity. The sensor using a SrCe0.95Yb0.05O3-α (SCY) electrolyte with a Pt electrode showed an enhancement of the mixed potential for the hydrocarbons by increasing the carbon number, branching the chain structure, and unsaturating the C-C linkage. The polarization curves for hydrocarbon oxidation and for oxygen reduction at the Pt/SCY interface were also measured. These results revealed that the mixed potential at the Pt/SCY interface was strongly dependent on the rate of abstraction of hydrogen atom from the hydrocarbon molecules.

DOI： 10.1021/jp012094k

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Journal of the Electrochemical Society  

Performance of a single-chamber solid oxide fuel cell was evaluated using a 0.15 mm thick Sm-doped ceria (SDC) electrolyte together with a 30 wl % SDC-Ni anode and a Sm0.5Sr0.5CoO3 cathode at heating temperatures below 500°C in a flowing mixture of butane and air. A large quantity of reaction heat, which was evolved by the partial oxidation of butane by oxygen at the anode, caused a temperature rise of more than 100°C at the anode, followed by thermal conduction to the cathode through the electrolyte. Simultaneously, the cell generated a large electromotive force of ca. 900 mV between the two electrodes. The resulting peak power density reached 245, 180, 105, and 38 mW cm 2 at heating temperatures of 450, 400, 350, and 300°C, respectively. The comparison of the butane fuel with the other hydrocarbon fuels showed that the fuel cell performance became enhanced, especially at reducing temperatures, as the carbon number of the hydrocarbon increased, and the chain structure was branched. © 2001 The Electrochemical Society. [DOI: 10.1149/1.1368098] All rights reserved.

DOI： 10.1149/1.1368098

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)  

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Electrochemical and Solid-State Letters  

Mixed-potential type sensors using different ion conducting electrolytes with a Pt working electrode have been fabricated to investigate a relationship between the sensing properties for hydrocarbons and ion conduction in the electrolyte under oxidizing conditions at 600°C. There was an increase in the mixed potential for propene with increasing proton conduction or decreasing oxide ion conduction. The sensor using a SrCe0.95Yb0.05O3-α electrolyte showed an enhanced mixed potential for C1-C4 hydrocarbons by increasing the carbon number, unsaturating the C-C linkage, and branching the chain structure. In addition, this sensor barely showed the mixed potential for hydrogen, carbon monoxide, and nitrogen monoxide.

DOI： 10.1149/1.1363128

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Language：Japanese   Publishing type：Research paper (scientific journal)  

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Journal of the Electrochemical Society  

The non-Nernstian behavior of zirconia-based electrochemical cells with various metal oxide electrodes for 0-500 ppm C1-C4 hydrocarbons, hydrogen, and carbon monoxide was studied in the presence of 10% oxygen at 600 °C. The cell using an In2O3 electrode exhibited a largely negative electromotive force (emf) for propene but gave moderately negative emfs for hydrogen and carbon monoxide. The addition of 0.1 wt % MnO2 to the In2O3 electrode significantly improved the selectivity of the parent electrode for propene over hydrogen and carbon monoxide. The negative emf of the cell using the MnO2-containing In2O3 electrode for the hydrocarbons became enhanced as the carbon number of the hydrocarbon increased, the C-C linkage was unsaturated, and the chain structure was branched. This enhanced effect, as well as the addition effect of MnO2, was discussed on the basis of the measurements of the polarization curves of the MnO2-containing In2O3 electrode for the hydrocarbons and oxygen and the nonelectrochemical oxidation of the hydrocarbons by oxygen. In addition, the MnO2-containing In2O3 electrode for the hydrocarbons was compared with an Au electrode with respect to sensitivity to the hydrocarbons and reproducibility of the sensing properties.

DOI： 10.1149/1.1344558

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Authorship：Lead author   Language：Japanese  

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)  

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Journal of the Electrochemical Society  

The Pt-catalyzed reduction of nitric oxide (NOx) using ethane as a reductant can be promoted by the application of positive potentials to the cell NO, C2H6, O2, Pt or (Pt + MxOy)|YSZ|Pt, air between 600 and 700°C. At an O2 concentration of 0% in the reactant gas stream, almost all of the oxygen species transported to the Pt catalyst through the yttria-stabilized zirconia is consumed in the reaction with NO and ethane, which cannot proceed by the supply of gaseous O2 in an amount equimolar to the transported oxygen species under open-circuit conditions. At O2 concentrations of 2-12% in the reactant gas stream, the oxygen species transported to the Pt catalyst shows a certain promotional effect on the reduction of NO by ethane. The promotional effect is further enhanced by the addition of 15 wt% Mn2O3 or 15 wt% MoO3 to the Pt catalyst: Both reaction rates at potentials of 2 V are ca. four times those under open-circuit conditions, although the reaction over the MoO3-containing Pt catalyst is accelerated by the application of not positive but negative potentials to the cell. The mechanism of the promotional effect is discussed on the overall kinetic studies.

DOI： 10.1149/1.1393968

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)  

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Journal of the Electrochemical Society  

The performance of a single-chamber solid oxide fuel cell (SOFC) was studied between 350 and 900 °C in flowing mixtures of methane, ethane, propane, or liquefied petroleum gas and air with a fuel/air volume ratio of one, where their oxidation proceeded safely without explosion. Among all tested electrode materials, Ni-Ce0.8Sm0.2O1.9 cermet and Sm0.5Sr0.5CoO3 oxide functioned best as the anode and cathode, respectively, in various gas mixtures. A cell constructed from a La0.9Sr0.1Ga0.8Mg0.2O3 electrolyte with the two electrodes generated>900 mV in a methane-air mixture between 600 and 800 °C and in an ethane-air mixture between 450 and 650 °C. A small electrode reaction resistance resulted in increasing power density with decreasing electrolyte thickness. The peak power density at 450 °C increased from 34 to 101 mW cm-2 with decreasing electrolyte thickness from 0.50 to 0.18 mm. The working mechanism of the single-chamber SOFC at different temperatures was also studied by measuring the catalytic activities of the two electrodes, for partial oxidation of the hydrocarbons.

DOI： 10.1149/1.1393621

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Language：Japanese   Publishing type：Research paper (scientific journal)  

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Science  

The performance of a single-chamber solid oxide fuel cell was studied using a ceria-based solid electrolyte at temperatures below 773 kelvin. Electromotive forces of ~900 millivolts were generated from the cell in a flowing mixture of ethane or propane and air, where the solid electrolyte functioned as a purely ionic conductor. The electrode-reaction resistance was negligibly small in the total internal resistances of the cell. The resulting peak power density reached 403 and 101 milliwatts per square centimeter at 773 and 623 kelvin, respectively.

DOI： 10.1126/science.288.5473.2031

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Solid State Ionics  

The electrochemical promotion of the decomposition of NO in the presence of excess O2 was carried out by applying AC voltages lower than 6 V at frequencies from 0.01 to 103 Hz to a YSZ cell having two same-metal electrodes, Au, Pd, Pt or Rh. The Pd and Pt electrodes were relatively effective for this reaction. This could be explained by their electrochemical oxygen-pumping properties and catalytic activities for the reduction of NO. The promotional effect was the most enhanced at a frequency of 0.1 Hz and became larger as the concentration of NO increased or the concentration of O2 decreased. Most of the product was N2, although a small amount of N2O was observed at low conversion of NO. The comparison of AC electrolysis with DC electrolysis showed that the former had a somewhat lower current efficiency for the decomposition of NO than the latter at lower than 3 V, above which the opposite result was observed. In addition, DC electrolysis brought about a significant deterioration of the cell, but AC electrolysis did not result in such a deterioration even at a high voltage of 4 V.

DOI： 10.1016/S0167-2738(00)00581-6

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Solid State Ionics  

The electrochemical promotion of the decomposition of NO by applying an AC voltage to a YSZ cell having two Pd electrodes has been modified by calcining the Pd electrode at 1450 °C and then coating the obtained Pd electrode with Rh metal. The calcination of the Pd electrode at 1450 °C depressed the oxidation of Pd to PdO at temperatures lower than 800 °C. The coating of the Pd electrode with Rh increased the catalytic activity for the decomposition of NO at temperatures lower than 800 °C. As a result, these modifications enhanced the current efficiency for the decomposition of NO at low temperatures from 650 to 450 °C and at high concentrations of O2 from 2 to 13%. No negative effect on the decomposition of NO was observed in the presence of 5% water vapor and 5% CO2, while a positive effect on this reaction was found for the presence of 500 ppm CH4, C3H8 and C5H12. Based on the measurements of the selectivity for N2 over N2O and the decomposition of N2O, it was concluded that NO is reduced to N2 via intermediate N2O, especially at low temperatures.

DOI： 10.1016/S0167-2738(00)00508-7

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)  

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Language：Japanese   Publishing type：Research paper (scientific journal)  

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)  

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Journal of the Electrochemical Society  

The performance of a single-chamber solid-oxide fuel cell (SOFC) made from an yttria-stabilized zirconia solid electrolyte with a 25 wt% Ce0.8Gd0.2O1.9 (GDC)-containing Ni anode and a 15 wt% MnO2-containing La0.8Sr0.2MnO3 cathode was found to be significantly enhanced by the deposition of Mn, Ga, Cr, Ce, and Lu oxide layers on the YSZ surface. In particular, the deposition of the Mn oxide layer increased the maximum power density from 161 to 213 mW cm-2 in a mixture of methane and air having a volume ratio of methane to oxygen of 1/1 at a flow rate of 300 mL min-1 (methane 52 mL min-1, oxygen 52 mL min-1, nitrogen 196 mL min-1), and at an operating temperature of 950°C. This effect was the result of the promoted anodic and cathodic reactions. Two types of cell designs were examined for the single-chamber SOFC; the two electrodes were deposited on opposite surfaces (A-type cell) and on the same face (B-type cell) of the solid electrolyte. The A-type cell showed an increasing power density with decreasing thickness of the solid electrolyte. The maximum power density was 256 mW cm-2 at a solid electrolyte thickness of 0.3 mm. The B-type cell showed an increased power density for a decreased gap between the two electrodes. The maximum power density was 143 mW cm-2 for a gap of 0.5 mm between the two electrodes. In addition, the long-term stability of the single-chamber SOFC was also studied and found to have a direct relationship with the carbon deposition on the GDC-containing Ni electrode.

DOI： 10.1149/1.1393359

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Solid State Ionics  

An excellent SOFC performance in a mixture of methane and air is achieved by constructing a one-chamber cell from a YSZ solid electrolyte with a 25 wt.% Ce0.8Gd0.2O1.9 (GDC)-added Ni anode and 15 wt.% MnO2-added La0.8Sr0.2MnO3 (LSM) cathode, which are deposited on opposite surfaces (A-type cell) or the same face (B-type cell) of the solid electrolyte. Experiments are carried out in a mixture of methane and air having a volume ratio of methane to oxygen of 1/1 at a flow rate of 300 ml min-1 (methane 52 ml min-1; oxygen 52 ml min-1; nitrogen 196 ml min-1) and at an operating temperature of 950 °C. The A-type cell shows an increasing power density with decreasing thickness of the solid electrolyte. The maximum power density is 204 mW cm-2 at a solid electrolyte thickness of 0.3 mm. The B-type cell shows an increasing power density with decreasing gap between the two electrodes. The maximum power density is 102 mW cm-2 for a gap between the two electrodes of 1 mm. The working mechanism of the one-chamber SOFC and the addition effects of GDC and MnO2 are studied using a two-chamber cell which permits independent evaluations of the Ni- and LSM-based electrodes.

DOI： 10.1016/S0167-2738(99)00253-2

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Language：Japanese   Publishing type：Research paper (scientific journal)  

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Authorship：Lead author   Language：Japanese  

Language：Japanese   Publishing type：Research paper (scientific journal)  

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Sensors and Actuators, B: Chemical  

An electrochemical device for detecting various hydrocarbons at high temperatures has been fabricated by attaching two Pd|YSZ|Au cells together in which the Pd electrodes are located on the inside of the assembly. The sensing properties for C1-C6 alkanes, C2-C4 alkenes and C6-C8 aromatic hydrocarbons were investigated at 700 °C. When the sample gases containing 0-1000 ppm hydrocarbon and 250-1000 ppm oxygen were supplied to the device at a flow rate of 100 cm3 min-1, large electromotive force (EMF) values were generated from one cell and then compensated by electrochemically pumping oxygen from the other cell. The current applied to the latter cell increased with increasing hydrocarbon concentration and was not significantly affected by changing the oxygen concentration. In addition, the sensitivity to the hydrocarbons became higher as the carbon number of the hydrocarbons increased, although this did not hold for the aromatic hydrocarbons.

DOI： 10.1016/S0925-4005(99)00247-6

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)  

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Electrochemical and Solid-State Letters  

The sensing properties of zirconia-based electrochemical cells with various metal oxide electrodes for 0-500 ppm hydrocarbons (primarily propene), hydrogen, and carbon monoxide were studied in the presence of 10% oxygen at 600 °C. The addition of 0.1 wt % manganese oxide (MnO2) to an indium oxide (In2O3) electrode significantly improved the selectivity of the parent electrode to propene over hydrogen and carbon monoxide. This addition effect was based on the promotion of nonelectrochemical oxidations of hydrogen and carbon monoxide in preference to that of propene. The sensor using the 0.1 wt % MnO2-added In2O3 electrode was more reproducible and sensitive to the hydrocarbons than that using a gold electrode.

DOI： 10.1149/1.1390937

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Language：Japanese   Publishing type：Research paper (scientific journal)  

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Journal of the Electrochemical Society  

It was found that the non-Nernstian behavior of a stabilized zirconia cell using a gold (Au) working electrode for saturated and unsaturated hydrocarbon gases can be markedly enhanced by adding tantalum oxide (Ta2O5) to the Au electrode. The non-ideal emf value of the cell using the 10 wt% Ta2O5-added Au electrode for propene is typically three times the value of the cell using the parent Au electrode. The enhancing effect is explained by a promotion of the anodic reaction of propene in preference to the cathodic reaction of oxygen, which simultaneously occurs at the working electrode. The non-ideal emf value for hydrocarbons becomes more negative as the carbon number increases, the C-C linkage is unsaturated, and the chain structure is branched. The enhancing effect due to the calcination of the Au electrode at high temperatures was also studied and was found to be based on a depression of the cathodic reaction of oxygen rather than the anodic reaction of propene.

DOI： 10.1149/1.1392478

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Language：Japanese   Publishing type：Research paper (scientific journal)  

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Journal of the Electrochemical Society  

A one-chamber solid oxide fuel cell (working in a methane-air mixture) with yttria-stabilized zirconia (YSZ) electrolyte was modified by adding oxide to the anode (Pt) and cathode (Au). It was determined that the addition of MnO2 to both electrodes significantly improved the cell discharge characteristics. The short-circuit current density of a cell using 15 wt % MnO2 added to the Pt and 20 wt % MnO2 added to the Au was about 50 times larger than that of a cell using Pt and Au electrodes. Moreover, the cell performance was enhanced further when 1 wt % MnO2 was doped into the YSZ electrolyte. Microstructural observations of the YSZ electrolyte/electrodes interfaces that both the electrode porosity and the contact areas between electrodes and YSZ electrolyte increased markedly for the MnO2-containing Pt and Au electrodes. In addition, the electrocatalytical property of MnO2 added in the electrodes may also contribute to the improved cell performance.

DOI： 10.1149/1.1392014

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Language：Japanese   Publishing type：Research paper (scientific journal)  

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Electrochemical and Solid-State Letters  

A single chamber cell constructed from an yttria-stabilized zirconia solid electrolyte with a nickel anode and a strontium-doped lanthanum manganese oxide (La0.8Sr0.2MnO3) cathode can generate an electromotive force (emf) of 795 mV and a power density of 121 mW cm-2 in a mixture of methane and air at a flow rate of 300 mL min-1 and 950 °C. The simultaneous additions of 25 wt % gadolinium-doped cerium oxide (Ce0.8G0.2dO1.9) and 15 wt % manganese oxide (MnO2) to the anode and cathode, respectively, further increased the emf to 833 mV and the power density to 162 mW cm-2.

DOI： 10.1149/1.1390822

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Language：Japanese   Publishing type：Research paper (scientific journal)  

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Authorship：Lead author   Language：Japanese  

Authorship：Lead author   Language：Japanese  

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Journal of the Electrochemical Society  

A sensor element detecting propylene at high temperatures has been fabricated by attaching two Pd or Pt|YSZ|Au cells together where the Pd or Pt electrodes were located on the inside of the assembly. The sensing properties of the sensor at 750°C were investigated using a flowing mixture of propylene, methane, carbon monoxide, and oxygen, the concentrations of which were in the range of 100 to 700 ppm. The sensor element using the Pd electrode had a high sensitivity to propylene, but a low selectivity to propylene over methane. The use of the Pt electrode made it possible to significantly improve the selectivity to propylene over methane, because the catalytic activities of the Pt electrode for the oxidation of methane were far lower than that of the Pd electrode and as low as that of the Au electrode. The current signal at a fixed oxygen concentration of 300 ppm was almost proportional to the propylene concentration. In addition, the current signal at a fixed propylene concentration of 350 ppm was not significantly affected by changing the oxygen concentration. © 1999 The Electrochemical Society. S0013-4651(98)04-049-X. All rights reserved.

DOI： 10.1149/1.1391618

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Electrochemical and Solid-State Letters  

Non-Nernstian behaviors of a zirconia-based oxygen sensor for 0-500 ppm saturated and unsaturated hydrocarbon gases were studied in the presence of 10% oxygen at 600°C. The sensor, using an Au sensing electrode, produced large electromotive forces (emfs) for the unsaturated hydrocarbons which were aliphatic as well as aromatic. The emf values of the sensor for the hydrocarbons were strongly affected by their unsaturation fraction, carbon number, and chain structure. © 1998 The Electrochemical Society. All rights reserved.

DOI： 10.1149/1.1390683

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Solid State Ionics  

The detection of NO in the presence of excess oxygen has been carried out using four electrochemical cells, Pt|YSZ|Pt, which serve as an electrochemical pumping cell, an electrolysis cell and two oxygen sensors, respectively. Their operation temperature was 800°C. A mixture of 0-2500 ppm NO, 1-7% oxygen, 3-10% water vapor and 0-10% carbon dioxide in argon was used as a sample gas. At the electrochemical pumping cell, oxygen in the sample gas was removed down to a constant concentration of 1800 ppm, which was monitored by the oxygen sensor. At the electrolysis cell, water vapor in the sample gas was electrolyzed, and the resulting hydrogen reacted with NO in the sample gas. Finally, the sample gas was fed into another oxygen sensor. Two potentiometric and amperometric methods were adopted to detect NO. In the potentiometric method, the EMF value of the oxygen sensor decreased with increasing NO concentration. In the amperometric method, the current applied to the electrolysis cell was proportional to the concentration of NO. Additionally, the influences of the coexisting oxygen, water vapor and carbon dioxide in the sample gas on the detection of NO were investigated in detail. © 1998 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/s0167-2738(97)00539-0

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Solid State Ionics  

The reaction of NO with the hydrogen formed by electrolyzing water vapour in a YSZ cell has been applied to detect NO with output signal of magnitude in millivolt or milliampere. The experimental apparatus consisted of two YSZ cells, Pt|YSZ|Pt, which served as an electrolysis cell and an oxygen sensor, respectively. A mixture of 0-3000 ppm NO and 3% H2O in argon was successively fed to the two cells at 800°C. In the upstream cell, the hydrogen formed by electrolyzing water vapour in the sample gas reacted with NO in the sample gas. In the downstream cell, the electromotive force (EMF) value was measured using air as a reference gas. The EMF value of the oxygen sensor was used as a sensor signal, when a current of 6.7 mA was applied to the electrolysis cell. The EMF signal decreased with increasing NO concentration in the sample gas. Furthermore, the current applied to the electrolysis cell was used as another sensor signal, when the EMF value of the oxygen sensor was held at 700 mV. The current signal increased with increasing NO concentration in the sample gas. © 1998 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/s0167-2738(97)00538-9

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Language：Japanese   Publishing type：Research paper (scientific journal)  

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Sensors and Actuators, B: Chemical  

A sensor device detecting propylene under oxidizing conditions at high temperatures has been fabricated using a yttria-stabilized zirconia (YSZ) as the solid electrolyte. When the sample gas containing 0-500 ppm propylene and 10 vol.% O2 was fed to various metal electrodes at 600°C, the Pt, Pd and Ni electrodes had a small or negligible EMF response, but the Au electrode had a large EMF response, which was based on a mixed potential. The mixed potentials of the Au electrode for H2, CO and CH4 were very small and that for propylene was independent of the presence of water vapor and CO2. However, since this sensor was an oxygen concentration cell, the mixed potential for propylene was affected by changing the O2 concentration. This problem was appreciably solved using a one-compartment cell attached with the Au and Pt electrodes, where their sensitivities to O2 were compensated by each other. In addition, the mechanism of the mixed potential for propylene was discussed by measuring the polarization curve of the Au electrode and its catalytic activity. © 1998 Elsevier Science S.A. All rights reserved.

DOI： 10.1016/S0925-4005(98)00217-2

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Solid State Ionics  

A sensor for detecting CH4 in exhaust gases from gasoline engines has been constructed from two Pd|YSZ| Au cells, which are attached to each other with their Pd electrodes in the interior side of the assembly. When the sample gases consisting of CH4, O2 and H2O were fed to the sensor element at 750°C, EMF values were generated from the one cell and then compensated by pumping O2 electrochemically from the other cell. Currents applied to the latter cell linearly increased with CH4 concentration, but were not influenced by changing O2 concentration.

DOI： 10.1016/s0167-2738(97)00405-0

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Solid State Ionics  

The mechanism of the NO decomposition in the presence of excess O2, H2O and CO2 using a ceria-based oxide ionic conductor with a Pd electrode has been studied by solid electrolyte potentiometry (SEP) method. A single compartment cell for measuring PO2 , Pt|YSZ|Pt, are attached to another single compartment cell for decomposing NO, Pd|Ce0.8Sm0.2O1.9|Pd, where their working electrodes come into contact with each other. Experiments were carried out with a mixture of 2611 ppm NO, 0.1-4% O2, 0-5% H2O and 0-5% CO2 in argon at 800°C. A PO2 measurement in the neighborhood of the Pd electrode during NO decomposition confirms that the NO decomposition is initiated after the electrochemical oxygen pump is completed. A comparison of the Pd electrodes heated at 850°C with that heated at 1300°C shows that the poorer the oxygen pumping property, the better the NO decomposition. On the basis of these results, the mechanism of the NO decomposition is discussed in detail. In addition, the SEP method also gives information about the influences of the coexistent O2, H2O and CO2 on the NO decomposition.

DOI： 10.1016/s0167-2738(97)00116-1

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Language：Japanese   Publishing type：Research paper (scientific journal)  

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Language：Japanese   Publishing type：Research paper (scientific journal)  

Web of Science

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Solid State Ionics  

The electrochemical oxygen pump has been studied using Ceo0.8Sm0.2O1.9 as a solid electrolyte and gold metal as an electrode. The O2 concentration in the flow of a mixture of 1000 ppm NO, 1-10% O2, 5% H2O and 5% CO2 at a flow-rate of 20 ml min-1 was electrochemically controlled to a constant value of 5% by applying anodic or cathodic currents to the cell at 900°C. During oxygen pumping, NO was not electrolyzed at all and the pumping amount of oxygen obeyed Faraday's law. A potentiometic-or amperometric-type sensor for NOx when introduced into the resulting gas stream, exhibited an output signal without influence of the O2 concentration.

DOI： 10.1016/s0167-2738(96)00541-3

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Language：English   Publishing type：Research paper (scientific journal)  

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Authorship：Lead author   Language：Japanese  

Authorship：Lead author   Language：Japanese  

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Kagaku Kogaku Ronbunshu  

The influence of initial agglomerate-size, gas velocity, and temperature on fluidizing behaviour and bed expansion of ultra-fine powders was examined by the use of a transparent set-up. The fluidizing behaviour was observed through transparent walls. Its behaviour was related to the change in primary agglom erate-size and the assumed secondary-one. The results showed that initial agglomerates were preservable to a certain degree during fluidization and that the size of the initial agglomerate considerably affected the fluidizing behaviour. Adsorbed water even binded strongly to the particle surface influencing secondary-agglomerate-size, and thus the amount of the adsorbed water significantly affected the fluidizing behaviour in the case of magnesia powder. Due to the formation of secondary agglomerates, incipient gas velocity increased at elevated temperature with decreasing initial agglomerate-size. It was found that a rise in gas velocity and bed expansion of up to 2 or 3 times cause almost no change in size of an assumed secondary agglomerate, at least in an uniform bed.

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Language：Japanese   Publishing type：Research paper (scientific journal)  

Web of Science

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Journal of the Chemical Society - Faraday Transactions  

Electrochemical removal of NO and CH4 from a gas stream containing excess O2, H2O and CO2 has been carried out between 400 and 800°C using a single-compartment reactor, which is constructed from CeO2-based solid electrolyte with two palladium electrodes. At all temperatures studied, both NO and CH4 were decomposed by applying a direct current to the reactor. NO was decomposed to N2 in two different ways depending on the applied current. At low currents, NO was electrolysed together with O2 at the palladium cathode; and, at high currents, NO was catalytically reduced over the palladium surface free from adsorbed oxygen. By investigating the influences of the concentration of NO, H2O, CO2, CH4 or C3H8 contained in the reactant gas to these two decompositions, their mechanisms are discussed in detail.

DOI： 10.1039/ft9969204297

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Language：Japanese   Publishing type：Research paper (scientific journal)  

Web of Science

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Applied Catalysis A: General  

The grinding operation of La0.8Sn0.2MnO3 (LSM) powder by a vibration mill has been carried out with the intention of giving a higher surface area and a good thermal stability. The specific surface area of the LSM powder increased with operation time and reached up to 34 m2 g-1 for 350 h. XRD measurement and chemical analysis showed that during the grinding operation, the crystal structure of the LSM powder was kept and that the extent of the contamination was negligibly small. In CH4 oxidation at 400°C and N2O reduction at 450°C over the ground LSM powder, both conversions were raised proportional to the increasing specific surface area. Furthermore, the thermal stability of the ground LSM powder was improved by grinding it together with CeO2 powder. The fine dispersion of CeO2 particles around the LSM particles effectively depressed the sintering of the LSM powder at elevated temperatures.

DOI： 10.1016/0926-860X(96)00166-4

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Solid State Ionics  

A novel design for the solid oxide fuel cell (SOFC) has been proposed. By attaching palladium and gold electrodes on the same face of BaCe0.8Gd0.2O3-α electrolyte and feeding a mixture of CH4 and O2 (CH4:O2 mole ratio = 2:1) to the cell at 950°C, electric power could be generated from the cell. The main advantages are that the ohmic resistance of the cell decreased with reducing distance between the two electrodes and that some unit cells were connected in series and parallel with one another on the same electrolyte. In addition, the surface ionic conduction of oxide ion was studied from the standpoint of the surface morphology of the electrolyte.

DOI： 10.1016/s0167-2738(96)00437-7

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Language：Japanese   Publishing type：Research paper (scientific journal)  

Web of Science

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Solid State Ionics  

Electrochemical removal of NO from a gas stream containing 2% O2, 5% H2O and 5% CO2 has been carried out between 400 and 800°C using a single-compartment reactor, constructed from CeO2-based solid electrolyte with two palladium electrodes. At all temperatures studied, NO was decomposed to N2 at the palladium cathode by applying a direct current to the reactor. The dependence of the conversion of NO to N2 on the concentration of NO, O2, H2O or CO2 was investigated at 450°C in detail.

DOI： 10.1016/0167-2738(96)00257-3

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Language：Japanese   Publishing type：Research paper (scientific journal)  

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Language：Japanese   Publishing type：Research paper (scientific journal)  

Web of Science

Language：Japanese   Publishing type：Research paper (scientific journal)  

Web of Science

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Journal of the Chemical Society - Faraday Transactions  

The oxidative coupling of CH4 to C2H4 and C2H6 (C2-hydrocarbons) has been carried out using an Li+ ion conductor as a solid electrolyte. A single-compartment cell is constructed from (Li2O)0.17(BaO)0.07(TiO2) 0.76 (LBT) ceramic with two gold electrodes. Alternative current voltages are applied between the two electrodes with a mixture of 8.3% CH4 and 1.6% O2 in argon. The experiments are carried out under various conditions. The formation of C2-hydrocarbons is the most effectively enhanced at a temperature of 850°C or a frequency of 10 Hz. For example, the conversion of CH4 and the selectivity of C2-hydrocarbons at 3 V are 2 and 1.5 times more than those at the open circuit, respectively. The applications of a dc voltage to a two-compartment cell suggested that the active sites are generated via the cathodic reaction. The mechanism for the formation of C2-hydrocarbons is discussed in detail.

DOI： 10.1039/ft9969202393

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Language：Japanese   Publishing type：Research paper (scientific journal)  

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Authorship：Lead author   Language：Japanese  

Authorship：Lead author   Language：Japanese  

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Journal of Applied Electrochemistry  

An electrochemical steam pump was operated at temperatures of 700-900deg;C using a high-temperature type protonic conductor, SrCe0.95Yb0.05O3-α, as a solid electrolyte. When wet air and dry air were introduced into the anode and cathode, respectively, and direct current was applied to the solid electrolyte, the partial pressure of water vapour decreased at the anode, while it increased at the cathode. At low current densities, the pumping rate of water vapour was increased by decreasing the operating temperature and increasing the partial pressure of water vapour at the anode. This is due to the change in proton transport number in SrCe0.95Yb0.05O3-α which depends on the operating condition. At high current densities, the pumping rate was limited by the diffusion rate of water vapour through the porous anode. © 1996 Chapman & Hall.

DOI： 10.1007/BF00683745

Scopus

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Denki Kagaku  

In order to find out a suitable electrolyte for a new-type SOFC (one chamber with methane - air mixture), YSZ (8 mol% Y2O3) doped with TiO2 was tested as a solid electrolyte. In the case of non-doped YSZ, the open - circuit voltage of the cell decreased with time, and the electric power density was extremely smaller than the value obtained in a conventional SOFC using YSZ as a solid electrolyte. However, in the case of YSZ doped with TiO2 (5 mol%), the electric power density was about 6 times higher than that in the case of YSZ only, although the terminal voltage of the cell-slightly decreased with time. This was based on the difference in cathodic polarization and transitional change in the potential between these electrolytes.

DOI： 10.5796/kogyobutsurikagaku.64.649

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Language：Japanese   Publishing type：Research paper (scientific journal)  

Web of Science

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Journal of the Chemical Society, Faraday Transactions  

Electrolysis of NO and CH4 in the presence of excess O2 has been studied using a single-compartment reactor, constructed from yttria-stabilized zirconia (YSZ), with two palladium electrodes. The palladium electrodes were attached by an electroless plating method. Experiments were conducted between 550 and 900 °C with a mixture of 1000 ppm NO, 1000 ppm CH4, 2% O2, 5% H2O and 5% CO2 in argon at a flow rate of 50 ml min-1. The reduction of NO to N2 and the oxidation of CH4 to CO2 were promoted by applying a direct current between the two palladium electrodes. The current efficiency for the reduction of NO was about 1.5% at all measured temperatures, while that for the oxidation of CH4 decreased from 2.7 to 0.3% with increasing temperature from 550 to 900 °C. The dc resistance of the reactor was mainly due to the ohmic resistance of the electrolyte. The transport properties of O2- through the electrolyte followed Faraday's law under operating conditions. These results were strongly dependent on the morphology and thickness of the palladium electrode.

DOI： 10.1039/FT9959101955

Scopus

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Journal of the Chemical Society, Faraday Transactions  

A membrane reactor for the oxidative coupling of CH4 has been constructed with an oxide ion-electron hole mixed conductor, BaCe0.8Gd0.2O3-α. 10% CH4 diluted with Ar and an O2-Ar mixture at a given ratio were fed into opposite sides of the membrane at 1173 K. The formation rate of C2-hydrocarbons (ethane and especially ethene) in the CH4 compartment increased with Po2 in the O2-Ar compartment. This enhancement was due to electrochemical oxygen permeation, causing the conductor to short-circuit itself, resulting form the mixed conduction. For comparison, 10% CH4 and a small amount of O2 were co-fed into one side of the membrane. The membrane operation gave a C2 selectivity two times that of the co-feed operation for all CH4 conversions. From a catalytic study using BaCe1-xGdxO3-α powders as catalyst, it was found that increasing both the oxide-ion and electron-hole conductivities enhanced the formation of C2 hydrocarbons, but reduced that of CO2. On the basis of these results, a mechanism for the oxidative coupling of CH4 of the mixed-conductor membrane was proposed.

DOI： 10.1039/FT9959104419

Scopus

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Journal of the Chemical Society, Chemical Communications  

When CH4 and O2 are fed into opposite sides of an electrochemical reactor using BaCe0.8Gd0.2O 3-α ceramic as a solid oxide membrane, the formation of C 2 hydrocarbons is enhanced by self-short circuiting the reactor owing to oxide ion and electron hole mixed conduction in the ceramic.

DOI： 10.1039/C39950001001

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Language：Japanese   Publishing type：Research paper (scientific journal)  

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Language：Japanese   Publishing type：Research paper (scientific journal)  

Web of Science

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Journal of the Electrochemical Society  

A novel solid oxide fuel cell (SOFC) system, which does not need to separate the supply of fuel and oxidant gases and generates electric power as well as chemicals, was studied. The fuel cell consisted of PtiBaCe08gY0.2O3_alAu, in which two electrodes were exposed to the same mixture of CH4 and air. Electromotive forces (EMFs) were about 700 ~ 800 mV at operating temperatures between 750 and 950°C, and terminal voltages were about 420 mV with discharge a current density of about 400 mA cm-2 (0.17 W cm-2) at 950°C and 350 mV with 75 mA cm-2 (0.03 W cm-2) at 750°C. The working mechanism of the fuel cell was clarified to be based on the difference in catalytic activity for the partial oxidation of methane between two electrode materials: the Pt catalyzes the partial oxidation of methane to form hydrogen and carbon monoxide, while the Au is inactive to this reaction. Therefore, the Pt acts as a fuel electrode, while the Au acts as an oxygen electrode at which electrochemical reduction of oxygen takes place on discharging the cell. © 1995, The Electrochemical Society, Inc. All rights reserved.

DOI： 10.1149/1.2049968

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Solid State Ionics  

A novel design for the solid oxide fuel cell (SOFC) has been proposed. By attaching palladium and gold electrodes on the same face of BaCe0.8Gd0.2O3-α electrolyte and feeding a mixture of CH4 and O2 (CH4:O2 mole ratio = 2:1) to the cell at 950 °C, an electric power could be generated from the cell. The main advantages are that the ohmic resistance of the cell decreased with reducing distance between the two electrodes and that some unit cells were connected in series and parallel with one another on the same electrolyte. © 1995.

DOI： 10.1016/0167-2738(95)00197-E

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Journal of the Electrochemical Society  

The activity and selectivity of a palladium catalyst for the partial oxidation of methane have been improved by attaching two palladium catalysts to the faces of a zirconia-based ceramic and by applying an ac voltage between the two catalysts. Experiments were conducted between 873 and 1273 K with a mixture of 6.6% methane and 3.3% oxygen in argon. AC voltages at a frequency of 60 Hz were applied to the reactor. Above 1073 K, the amounts of unreacted methane and oxygen decreased, and the yields of hydrogen and carbon monoxide (synthesis gas) increased. At an ac voltage of 3 V at 1273 K, the yield of synthesis gas was up to two times more than that under the open-circuit condition. This enhancement was better than that found by applying a dc voltage of 3 V, in which case the yield of synthesis gas was 1.3 times more than that under the open-circuit condition. © 1995, The Electrochemical Society, Inc. All rights reserved.

DOI： 10.1149/1.2049972

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Language：Japanese   Publishing type：Research paper (scientific journal)  

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Language：Japanese   Publishing type：Research paper (scientific journal)  

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Solid State Ionics  

BaCeO3-based ceramics exhibit both protonic and oxide ionic conduction at high temperatures. In order to investigate the relation between ionic conduction in these oxides and the valence of the dopant cation, divalent Ca-doped BaCeO3 oxides were synthesized and their conduction properties were studied comparing them with those of trivalent Y-doped ones. When the dopant cation was changed from Y to Ca, both protonic and oxide ionic conductivities decreased. TPD analysis and electrochemical tracer experiment showed that the decrease in protonic conductivity could be ascribed to the decrease both in proton concentration and its mobility in the oxides. © 1995.

DOI： 10.1016/0167-2738(95)00058-E

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Language：Japanese   Publishing type：Research paper (scientific journal)  

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Language：Japanese   Publishing type：Research paper (scientific journal)  

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Language：Japanese   Publishing type：Research paper (scientific journal)  

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Journal of the Electrochemical Society  

The electrocatalytic oxidation of methane to ethane and ethylene has been carried out using an Li+ ion conductor as a solid electrolyte. The electrochemical cell used was Au I (Li2O)0.17(BaO)0.07(TiO2)o.761 Au, and the experiments were conducted at 850°C with a mixture of 8.3% methane and 1.6% oxygen in argon. By applying an ac voltage of 3 V at a frequency of 10 Hz to the cell, the conversion of methane and the selectivity to C2 hydrocarbons were enhanced 2 and 1.5 times more than at the open circuit, respectively. © 1995, The Electrochemical Society, Inc. All rights reserved.

DOI： 10.1149/1.2048653

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Language：Japanese   Publishing type：Research paper (scientific journal)  

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Journal of Applied Electrochemistry  

An electrochemical cell, Pd|YSZ|Pd, was constructed in order to remove both NO and CH4 in the presence of excess oxygen. When direct current was supplied to the cell with a flow of a mixture of NO, CH4, O2, H2O and CO2 at 700° C, NO was reduced to nitrogen at the cathode, and CH4 was oxidized to COx at both the anode and cathode. At the cathode, the reduction of NO and the oxidation of CH4 proceeded with the removal of chemisorbed oxygen species from the Pd surface, and at the anode, the oxidation of CH4 was enhanced by forming an active oxygen atom. © 1995 Chapman & Hall.

DOI： 10.1007/BF00262956

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Research on Chemical Intermediates  

A chemical sensor and an electrochemical reactor without the need for the geometry of two electrode compartments have been fabricated using high temperature-type proton and oxide ion conductors, respectively. Pd|CaZr0.9In0.1O3-α Au, responds quickly to dilute hydrocarbons (CH4, C2H6 and C3Hg) in air at 700 °C and changes an electromotive force (EMF) in proportion to the hydrocarbon content. Pd | yttria-stabilized zirconia (YSZ) | Pd, can remove both NO and CH4 in the presence of excess O2 at 700 °C. By passing the direct current through the cell, NO is reduced to N2 at the cathode, and CH4 is oxidized to COx at the anode. The efficiency of removal is independent of the presence of H2O and CO2. © 1995 Springer.

DOI： 10.1163/156856795X00161

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

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Language：Japanese   Publishing type：Research paper (scientific journal)  

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Solid State Ionics  

An amperometric sensor to detect D2O in a mixture of H2O and D2O has been studied using CaZr0.9In0.1O3-α as a high temperature protonic conductor. When the sensor heated at 900°C was exposed to air passed through the H2O+D2O mixture at 20°C, it could respond to D2O in the concentration range of 5% to 100% with a 90% response time of about 15 min. The sensing mechanism was based on a H/D isotope effect on resistance of both bulk oxide and electrode reaction. From temperature programmed desorption (TPD) and complex impedance methods, it was found that an increase in bulk resistance was ascribed to a decrease in mobility of the charge carrier. Current interruption method indicated that overpotentials of both anodic and cathodic reactions were increased by replacing protons with deuterons. © 1994.

DOI： 10.1016/0167-2738(94)90223-2

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Language：Japanese   Publishing type：Research paper (scientific journal)  

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Journal of the Electrochemical Society  

An amperometric sensor for the measurement of D2O concentration in a mixture of H2O and D2O has been studied using CaZr0.9 ln0.13-a as a high temperature protonic conductor. When the sensor heated at 1173 K was exposed to air passed through the H20 + D20 mixture at 293 K, it could respond to D20 in the concentration range of 5 to 100% with a 90% response time of about 15 min. © 1994, The Electrochemical Society, Inc. All rights reserved.

DOI： 10.1149/1.2055176

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Language：Japanese   Publishing type：Research paper (scientific journal)  

Web of Science

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Journal of the Electrochemical Society  

A proton-hole mixed conduction in SrCe0.95Yb005O3_α ceramic has been studied under an asymmetrical atmosphere with respect to hydrogen species. The following electrochemical cell was constructed; (I) 1% hydrogen, Pt I specimen ceramic Pt, O2-Ar mixture (II) and electrochemical hydrogen permeation through this sample was examined under open and closed-circuit conditions. When the circuit was closed, the hydrogen or water vapor evolution rates at the cathode decreased with increasing partial pressure of oxygen in the cathode. From the conductivity measurement under various po2, it was confirmed that the main charge carrier except protons was a positive hole, and that this ceramic behaved as a proton-hole mixed conductor under the asymmetrical condition. When the circuit was open, water vapor evolved spontaneously, and its formation rates were enhanced with increasing po2, in compartment (II). These phenomena indicate that this cell is a self-short-circuited via hole conduction in the bulk, and that hydrogen permeates electrochemically from compartment (I) to (II). Further, based on the principle of hydrogen permeation due to the proton-hole mixed conduction, CH4 dimerization was carried out at 1173 K using SrCe0.95Yb0.05O3_a ceramic as a membrane reactor. Formation rates of C2-hy-drocarbons were enhanced markedly by self-short-circuiting the electrochemical reactor due to the mixed conduction. To clarify the mechanism for the acceleration of CH4 dimerization, the electrolytic synthesis of ethane from CH4 was carried out at 948 K using SrCe0.95Yb0.05O3-α, ceramic as a membrane reactor. © 1994, The Electrochemical Society, Inc. All rights reserved.

DOI： 10.1149/1.2054993

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Language：Japanese   Publishing type：Research paper (scientific journal)  

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