Faculty Profiles - SAITO, Nagahiro

Papers - SAITO, Nagahiro

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Solution plasma synthesis of Pt/ZnO/KB for photo-assisted electro-oxidation of methanol

Hu X., Ge C., Su N., Huang H., Xu Y., Zhang J., Shi J., Shen X., Saito N.

Journal of Alloys and Compounds Vol. 692 page： 848 - 854 2017

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Alloys and Compounds

A high electrocatalytic performance Pt/ZnO/KB is well fabricated by a solution plasma technique in water at atmospheric pressure. Their electrocatalytic performance toward methanol oxidation is evaluated in alkaline with light irradiation or in dark. The electrocatalytic activity of Pt is improved in dark because the distribution and reactive sites of Pt nanoparticles are improved by coupling ZnO. And higher electrocatalytic activity is detected under light irradiation because of synergistic effect of photo- (ZnO) and electro-catalyst (Pt). Compared with several morphologies ZnO, ZnO nanowires give better catalytic activity for methanol oxidation than porous ZnO nanosheets because ZnO nanowires possess better electron transport property and smaller resistance. Under light irradiation, Pt/ZnO/KB coupled with ZnO nanowires shows over 3 times higher catalytic activity (ca. 964 mA mgPt−1) than Pt/KB (ca. 306 mA mgPt−1). And the tolerance to CO-poisoning and stability of Pt/ZnO/KB are also improved. Therefore, Pt/ZnO/KB nanocomposite will be a highly efficient potential anode catalyst in DMFCs with light irradiation.

DOI： 10.1016/j.jallcom.2016.09.032

Solution plasma synthesis of a boron-carbon-nitrogen catalyst with a controllable bond structure

Lee S., Heo Y., Bratescu M.A., Ueno T., Saito N.

Physical Chemistry Chemical Physics Vol. 19 ( 23 ) page： 15264 - 15272 2017

Language：English Publishing type：Research paper (scientific journal) Publisher：Physical Chemistry Chemical Physics

Synthesis of boron-carbon-nitrogen (BCN) nanocarbon with a controllable bond structure for enhanced oxygen reduction reaction (ORR) activity and durability was performed using a new method of discharge in organic solution mixtures named the 'Solution Plasma Process'. Using selected precursors a new strategy for the simultaneous synthesis of nanocarbon co-doped with heteroatoms was found. The synergistic effect of N and B in an uncoupling bond state improved the formation of new active sites for the ORR performance by changing the electronic structure of the base carbon. Meanwhile, when B and N are bonded together, the BCN catalyst contributes to a reduced ORR activity by forming a balanced electronic structure in carbon. The BCN nanocarbon with an uncoupling bond state exhibits an enhanced ORR activity under alkaline conditions, with an onset potential of -0.25 V versus -0.31 V for B/N coupling and 3.43 transferred electrons during the ORR. Although the ORR activity of the B/N uncoupling nanocarbon was not as good as the typical Pt/C, the durability of this synthesized material (15.1% current decrease after 20000 s of operation) was significantly better than that of the Pt/C catalyst (61.5% current drop under the same conditions). After the durability test, the increase of the chemical states containing oxygen was higher for Pt/C than B/N uncoupling.

DOI： 10.1039/c6cp06063c

In-situ one-step synthesis of carbon-encapsulated naked magnetic metal nanoparticles conducted without additional reductants and agents

Kang J., Kim Y., Kim H., Hu X., Saito N., Choi J., Lee M.

Scientific Reports Vol. 6 2016.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Scientific Reports

C-encapsulated highly pure Ni, Co, and Fe magnetic nanoparticles (MNPs/C) were synthesized by an innovative one-step in-situ plasma in liquid method (solution plasma processing, SPP) without any additional reductants, agents, or treatment. Successful encapsulation of MNPs was demonstrated by using inductively coupled plasma-atomic emission spectrometry and cyclic voltammetry techniques. The obtained X-ray diffraction patterns and transmission electron microscopy images corresponded to MNPs with average diameters of 5 nm and good crystalline structure. The C capsules with spherical shapes (containing onion-like layers) were characterized by uniform sizes (ranging from 20 nm to 30 nm) and chain-like morphologies. The synthesized MNPs/C exhibited superparamagnetic properties at room temperature and might be utilized in data storage, biomedical, and energy applications since various NPs (including bimetallic ones) could be easily prepared by changing working electrodes. This study shows the potential of SPP to be a candidate for the next-generation synthesis method of NPs/C.

DOI： 10.1038/srep38652

Fastest Formation Routes of Nanocarbons in Solution Plasma Processes

Morishita T., Ueno T., Panomsuwan G., Hieda J., Yoshida A., Bratescu M., Saito N.

Scientific Reports Vol. 6 2016.11

Language：English Publishing type：Research paper (scientific journal) Publisher：Scientific Reports

Although solution-plasma processing enables room-temperature synthesis of nanocarbons, the underlying mechanisms are not well understood. We investigated the routes of solution-plasma-induced nanocarbon formation from hexane, hexadecane, cyclohexane, and benzene. The synthesis rate from benzene was the highest. However, the nanocarbons from linear molecules were more crystalline than those from ring molecules. Linear molecules decomposed into shorter olefins, whereas ring molecules were reconstructed in the plasma. In the saturated ring molecules, C-H dissociation proceeded, followed by conversion into unsaturated ring molecules. However, unsaturated ring molecules were directly polymerized through cation radicals, such as benzene radical cation, and were converted into two- and three-ring molecules at the plasma-solution interface. The nanocarbons from linear molecules were synthesized in plasma from small molecules such as C2 under heat; the obtained products were the same as those obtained via pyrolysis synthesis. Conversely, the nanocarbons obtained from ring molecules were directly synthesized through an intermediate, such as benzene radical cation, at the interface between plasma and solution, resulting in the same products as those obtained via polymerization. These two different reaction fields provide a reasonable explanation for the fastest synthesis rate observed in the case of benzene.

DOI： 10.1038/srep36880

Effect of electron acceptors H<inf>2</inf>O<inf>2</inf> and O<inf>2</inf> on the generated reactive oxygen species <sup>1</sup>O<inf>2</inf> and OH<sup>·</sup> in TiO<inf>2</inf>-catalyzed photocatalytic oxidation of glycerol

Jedsukontorn T., Meeyoo V., Saito N., Hunsom M.

Cuihua Xuebao/Chinese Journal of Catalysis Vol. 37 ( 11 ) page： 1975 - 1981 2016.11

Language：English Publishing type：Research paper (scientific journal) Publisher：Cuihua Xuebao/Chinese Journal of Catalysis

The effect of the electron acceptors H2O2 and O2 on the type of generated reactive oxygen species (ROS), and glycerol conversion and product distribution in the TiO2-catalyzed photocatalytic oxidation of glycerol was studied at ambient conditions. In the absence of an electron acceptor, only HO· radicals were generated by irradiated UV light and TiO2. However, in the presence of the two electron acceptors, both HO· radical and 1O2 were produced by irradiated UV light and TiO2 in different concentrations that depended on the concentration of the electron acceptor. The use of H2O2 as an electron acceptor enhanced glycerol conversion more than O2. The type of generated value-added compounds depended on the concentration of the generated ROS.

DOI： 10.1016/S1872-2067(16)62519-6

Differences in intermediate structures and electronic states associated with oxygen adsorption onto Pt, Cu, and Au clusters as oxygen reduction catalysts

Morishita T., Ueno T., Panomsuwan G., Hieda J., Bratescu M., Saito N.

Journal of Physics D: Applied Physics Vol. 49 ( 41 ) 2016.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Physics D: Applied Physics

We used ab initio molecular orbital (MO) calculations to study the differences in the intermediate structures and the electronic states involved in the adsorption of O2 onto 13-atom metal clusters of Pt, Cu, and Au. Additionally, the conditions required for the electrocatalytic oxygen reduction reaction (ORR) on the Pt, Cu, and Au clusters were investigated and discussed. The intermediates involved in O2 adsorption onto Pt, Cu, and Au were found to be (Pt-O)-(Pt-O), Cu-O, and Au-O2, respectively. The differences in the O2 adsorption intermediates is explained on the basis of our analysis of the projected density of state (PDOS) area of the new MOs produced from a mixture of the 2pπ ∗ orbitals of O2 and the d orbitals of the metal clusters. The formation of the (Pt-O)-(Pt-O) intermediate after the adsorption of O2 onto the Pt cluster is attributed to the emergence of an antibonding orbital above the Fermi level. Thus, this electronic state can lead to the decomposition and desorption of O2 molecules, thereby promoting the high-activity level of ORR. For the Cu cluster, a new antibonding orbital was observed below the Fermi level. Moreover, the Cu cluster surface can only promote O2 decomposition and not O2 desorption due to the formation of copper oxides. For the Au cluster, no new MOs related to 2pπ ∗ orbitals of O2 appeared because O2 was molecularly adsorbed, implying that the Au cluster is an inefficient ORR catalyst.

DOI： 10.1088/0022-3727/49/41/415305

Fabrication of bacterial cellulose-ZnO composite via solution plasma process for antibacterial applications

Janpetch N., Saito N., Rujiravanit R.

Carbohydrate Polymers Vol. 148 page： 335 - 344 2016.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Carbohydrate Polymers

Zinc oxide (ZnO) was successfully synthesized by applying a solution plasma, a plasma discharge in a liquid phase, without the addition of a reducing agent and simultaneously deposited into a bacterial cellulose pellicle that functioned as a template. By the reasons of its nano-sized structure as well as favorable porous configuration, the BC pellicle has been proved to be a splendid upholding template for the coordination of ZnO. In addition, the ZnO-deposited BC composites demonstrated strong antibacterial activity without a photocatalytic reaction against both Staphylococcus aureus and Escherichia coli. Hence, the ZnO-deposited BC composites can be used as an antibacterial material in wound dressing and water disinfection applications.

DOI： 10.1016/j.carbpol.2016.04.066

Heterocarbon nanosheets incorporating iron phthalocyanine for oxygen reduction reaction in both alkaline and acidic media

Hyun K., Ueno T., Panomsuwan G., Li O., Saito N.

Physical Chemistry Chemical Physics Vol. 18 ( 16 ) page： 10856 - 10863 2016.4

Language：English Publishing type：Research paper (scientific journal) Publisher：Physical Chemistry Chemical Physics

Heterocarbon nanosheets incorporating iron phthalocyanine (FP-NCNs-SP) have been successfully synthesized by a facile one-pot solution plasma process at high repetition frequency. It was found that the Fe-N4 catalytic active sites could be preserved on the FP-NCNs-SP without degradation. The FP-NCNs-SP also possessed large surface area, good conductivity and high degree of graphitization. Electrochemical evaluations demonstrated that NCNs-SP had excellent electrocatalytic activity and selectivity toward oxygen reduction reaction (ORR) in alkaline medium through a direct four-electron pathway. Although the significant improvement in ORR activity was clearly observed in acidic medium, it was much poorer than in alkaline medium. We believe that the results presented in this work will shed light on the advanced synthesis and design of ORR electrocatalysts at room temperature with an abundance of catalytically active sites and high ORR performance.

DOI： 10.1039/c5cp07739g

High Efficiency DNA Extraction by Graphite Oxide/Cellulose/Magnetite Composites Under Na<sup>+</sup> Free System

Akceoglu G., Li O., Saito N.

JOM Vol. 68 ( 4 ) page： 1071 - 1077 2016.4

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

DNA extraction is the key step at various research areas like biotechnology, diagnostic development, paternity determination, and forensic science. Solid support extraction is the most common method for DNA purification. In this method, Na+ ions have often been applied as binding buffers in order to obtain high extraction efficiency and high quality of DNA; however, the presence of Na+ ions might be interfering with the downstream DNA applications. In this study, we proposed graphite oxide (GO)/magnetite composite/cellulose as an innovative material for Na+-free DNA extraction. The total wt.% of GO was fixed at 4.15% in the GO/cellulose/magnetite composite. The concentration of magnetite within the composites were controlled at 0–3.98 wt.%. The extraction yield of DNA increased with increasing weight percentage of magnetite. The highest yield was achieved at 3.98 wt.% magnetite, where the extraction efficiency was reported to be 338.5 ng/µl. The absorbance ratios between 260 nm and 280 nm (A260/A280) of the DNA elution volume was demonstrated as 1.81, indicating the extracted DNA consisted of high purity. The mechanism of adsorption of DNA was provided by (1) π–π interaction between the aromatic ring in GO and nucleobases of DNA molecule, and (2) surface charge interaction between the positive charge magnetite and anions such as phosphates within the DNA molecules. The results proved that the GO/cellulose/magnetite composite provides a Na+-free method for selective DNA extraction with high extraction efficiency of pure DNA.

DOI： 10.1007/s11837-016-1826-0

Nitrogen-Doped Carbon Nanoparticle-Carbon Nanofiber Composite as an Efficient Metal-Free Cathode Catalyst for Oxygen Reduction Reaction

Panomsuwan G., Saito N., Ishizaki T.

ACS Applied Materials and Interfaces Vol. 8 ( 11 ) page： 6962 - 6971 2016.3

Language：English Publishing type：Research paper (scientific journal) Publisher：ACS Applied Materials and Interfaces

Metal-free nitrogen-doped carbon materials are currently considered at the forefront of potential alternative cathode catalysts for the oxygen reduction reaction (ORR) in fuel cell technology. Despite numerous efforts in this area over the past decade, rational design and development of a new catalyst system based on nitrogen-doped carbon materials via an innovative approach still present intriguing challenges in ORR catalysis research. Herein, a new kind of nitrogen-doped carbon nanoparticle-carbon nanofiber (NCNP-CNF) composite with highly efficient and stable ORR catalytic activity has been developed via a new approach assisted by a solution plasma process. The integration of NCNPs and CNFs by the solution plasma process can lead to a unique morphological feature and modify physicochemical properties. The NCNP-CNF composite exhibits a significantly enhanced ORR activity through a dominant four-electron pathway in an alkaline solution. The enhancement in ORR activity of NCNP-CNF composite can be attributed to the synergistic effects of good electron transport from highly graphitized CNFs as well as abundance of exposed catalytic sites and meso/macroporosity from NCNPs. More importantly, NCNP-CNF composite reveals excellent long-term durability and high tolerance to methanol crossover compared with those of a commercial 20 wt % supported on Vulcan XC-72. We expect that NCNP-CNF composite prepared by this synthetic approach can be a promising metal-free cathode catalyst candidate for ORR in fuel cells and metal-air batteries.

DOI： 10.1021/acsami.5b10493

Electrocatalytic oxygen reduction on nitrogen-doped carbon nanoparticles derived from cyano-aromatic molecules via a solution plasma approach

Panomsuwan G., Saito N., Ishizaki T.

Carbon Vol. 98 page： 411 - 420 2016.3

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

Metal-free nitrogen-doped carbon nanoparticles (NCNPs) have been synthesized via a solution plasma process with the potential to achieve uniformly distributed nitrogen atoms. A set of cyano-aromatic molecules, including benzonitrile, 2-cyanopyridine, and cyanopyrazine, were used as a single-source precursor in the synthesis without the addition of a metal catalyst source. The resultant NCNPs reveal uniformly nanosized particles (20-40 nm) and an interconnected hierarchical pore structure with a high specific surface area (210-250 m2 g-1). The difference in carbon/nitrogen mole ratios of organic precursors gives rise to the variation of nitrogen-doping level in NCNPs from 0.63 to 1.94 atom %. Detailed electrochemical evaluation toward the oxygen reduction reaction (ORR) demonstrates that NCNPs exhibit a significant improvement in terms of both onset potential and current density under alkaline and acidic conditions. The predominant distribution of graphitic-N and pyridinic-N sites on NCNPs plays an essential role in enhancing the ORR activity and the selectivity toward a four-electron reduction pathway. More importantly, NCNPs possess excellent robust long-term durability and strong methanol tolerance compared with those of a commercial Pt/carbon catalyst.

DOI： 10.1016/j.carbon.2015.11.013

Synthesis of Fe-Cu bi-functional catalysts by solution plasma process for li-air battery application

Li O.L., Takahashi R., Urashima K., Saito N.

International Journal of Plasma Environmental Science and Technology Vol. 10 ( 1 ) page： 51 - 56 2016.3

Language：English Publishing type：Research paper (scientific journal) Publisher：International Journal of Plasma Environmental Science and Technology

This research reported an innovative method to synthesize inexpensive and bi-functional catalyst electrode material for the application in Li-air battery. Non-novel metal, Cu and Fe were served, respectively, as alternative Oxygen Reduction Reaction (ORR) and Oxygen Evolution Reaction (OER). Solution Plasma Process was applied to synthesized Cu-Fe metal nanoparticles and carbon nanoparticles simultaneously. SPP was generated in benzene 100 mL using a bipolar pulse power supply. Iron and copper of diameter 1.0 mm were used for the discharge electrode and precursor of the bimetallic nanoparticles. Solution was reacted and stirred continuously for 20 minutes. Based on the amount of electrode consumption and ICP-AES analysis, the percentage of Cu and Fe supported on carbon were respectively, 2.8 and 1.0 wt%. The diameter of metal nanoparticles was approximately 10 nm, where the carbon nanoparticles ranged between 20-30 nm. From XRD analyses, the presences of Cu, Fe and CuFe2O4 were confirmed. In the performance of cyclic voltammetry, Fe and Cu nanoparticles showed the catalytic activity, respectively, for ORR and OER, at -0.38 and above 0.5 V. In the case of Fe-Cu bimetallic nanoparticles, it showed the combined catalytic activities of the single particles.

Analysis of benzoquinone decomposition in solution plasma process

Bratescu M., Saito N.

Journal of Instrumentation Vol. 11 ( 1 ) 2016.1

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Instrumentation

The decomposition of p-benzoquinone (p-BQ) in Solution Plasma Processing (SPP) was analyzed by Coherent Anti-Stokes Raman Spectroscopy (CARS) by monitoring the change of the anti-Stokes signal intensity of the vibrational transitions of the molecule, during and after SPP. Just in the beginning of the SPP treatment, the CARS signal intensities of the ring vibrational molecular transitions increased under the influence of the electric field of plasma. The results show that plasma influences the p-BQ molecules in two ways: (i) plasma produces a polarization and an orientation of the molecules in the local electric field of plasma and (ii) the gas phase plasma supplies, in the liquid phase, hydrogen and hydroxyl radicals, which reduce or oxidize the molecules, respectively, generating different carboxylic acids. The decomposition of p-BQ after SPP was confirmed by UV-visible absorption spectroscopy and liquid chromatography.

DOI： 10.1088/1748-0221/11/01/C01009

Adsorption of carbon dioxide by solution-plasma-synthesized heteroatom-doped carbon nanospheres

Thongwichit N., Helena Li O.L., Yaowarat W., Saito N., Suriyapraphadilok U.

Japanese Journal of Applied Physics Vol. 55 ( 1 ) 2016.1

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

Porous carbon nanospheres (CNSs) synthesized by a plasma-in-liquid technique were applied as an adsorbent for CO2 adsorption. Two different types of aromatic solvents, benzene and pyridine, were used as precursors to generate CNSs. The prepared CNSs were carbonized and then activated with CO2 to obtain carbon materials with a suitable porous structure for CO2 adsorption. To improve CO2 adsorption capacity, activated CNSs were then chemically modified using different approaches of surface treatment, namely, HNO3 oxidation, amination without HNO3 preoxidation, and amination with HNO3 preoxidation. The CO2 adsorption capacities of the samples were investigated at 1 atm and 40 °C using a simultaneous thermal analyzer. It was found that the CO2 adsorption of CNSs was enhanced through the development of textural properties. All of the surface treatment approaches led to the increase in CO2 adsorption capacity of the activated CNSs owing to the presence of nitrogen or oxygen functional groups introduced onto the carbon surface during the treatment.

DOI： 10.7567/JJAP.55.01AE10

Highly durable silica-coated Pt/carbon nanotubes for proton-exchange membrane fuel cells application

Yaowarat W., Helena Li O.L., Saito N.

Japanese Journal of Applied Physics Vol. 55 ( 1 ) 2016.1

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

Platinum nanoparticles supported on carbon nanotubes (Pt/CNTs) have been used as an electrocatalyst in proton-exchange membrane fuel cells (PEMFCs). These catalysts show higher activity in oxygen reduction reaction in PEMFCs than conventional carbon-black-supported Pt nanoparticles. However, their durability is lower than that of other metal-alloy-based or nonmetal-based catalysts. In this study, Pt/CNTs were synthesized by solution plasma followed by coating with silica layer by the sol-gel method using a cationic surfactant [cetyltrimethylammonium bromide (CTAB)]. This material can be used as a cathode in PEMFCs. The silica layer was coated on the surface of Pt/CNTs to prevent agglomeration and detachment of Pt nanoparticles from carbon nanotubes during operation. The formation of silica layers significantly improved the durability of the Pt/CNT catalysts under acidic conditions. After 300 cycles of the cyclic voltammetry test in 0.5#M sulfuric acid (H2SO4), silicacoated Pt/CNTs increased the durability by 43.0 and 24.0% compared with those of noncoated commercial Pt/C and Pt/CNTs, respectively.

DOI： 10.7567/JJAP.55.01AE23

Synthesis of nitrogen-containing carbon by solution plasma in aniline with high-repetition frequency discharges

Hyun K., Ueno T., Saito N.

Japanese Journal of Applied Physics Vol. 55 ( 1 ) 2016.1

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

Nitrogen-containing carbon nanoparticles were synthesized in aniline by solution plasma with high-repetition frequency discharges. We developed a bipolar pulsed power supply that can apply high-repetition frequencies ranging from 25 to 200 kHz. By utilizing high-repetition frequencies, conductive carbons were directly synthesized. The crystallinity was increased and H/C ratio of carbon was decreased. Furthermore, nitrogen atoms were simultaneously embedded in the carbon matrix. Due to the presence of nitrogen atoms, the conductivity and electrocatalytic activity of the samples were remarkably improved compared to that of a pure carbon matrix synthesized from a benzene precursor.

DOI： 10.7567/JJAP.55.01AE18

Synthesis of SnO<inf>2</inf> nanoparticles using a solution plasma and their gas-sensing properties

Zhang J., Hu X., Shi J., Lu P., Shen X., Xu P., Saito N.

Japanese Journal of Applied Physics Vol. 55 ( 1 ) 2016.1

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

A simple solution plasma method was applied to the synthesis of SnO2 nanoparticles directly from tin(II) chloride solution, without adding any precipitant, stabilizer, or other agents at atmospheric pressure, because solution plasma provides a reaction field with a highly excited energy state. The results of X-ray power diffraction (XRD) analysis and transmission electron microscopy (TEM) verified that well-crystallized SnO2 nanoparticles in the size range of 2-5 nm were synthesized. SnO2 nanoparticles show satisfactory sensitivities to acetaldehyde and ethanol.

DOI： 10.7567/JJAP.55.01AE17

A simple synthesis method for nanostructured Co-WC/carbon composites with enhanced oxygen reduction reaction activity

Kang J., Kim H., Saito N., Lee M.

Science and Technology of Advanced Materials Vol. 17 ( 1 ) page： 37 - 44 2016

Language：English Publishing type：Research paper (scientific journal) Publisher：Science and Technology of Advanced Materials

Co nanoparticles (Co NPs) and nanoscale tungsten carbide (WC) are successfully synthesized simultaneously with mesoporous structured carbon black (C) using an innovative simple method, which is known as solution plasma processing (SPP), and NPs are also loaded onto carbon black at the same time by SPP. The introduction of Co NPs led to not only superior oxygen reduction reaction (ORR) activity in terms of onset potential and peak potential, but also to a more efficient electron transfer process compared to that of pure WC. Co-WC/C also showed durability for long-term operation better than that of commercial Pt/C. These results clearly demonstrate that the presence of Co NPs significantly enhanced the ORR and charge transfer number of neighboring WC NPs in ORR activities. In addition, it was proved that SPP is a simple method (from synthesis of NPs and carbon black to loading on carbon black) for the large-scale synthesis of NP-carbon composite. Therefore, SPP holds great potential as a candidate for nextgeneration synthetic methods for the production of NP-carbon composites.

DOI： 10.1080/14686996.2016.1140305

DFT calculation of oxygen adsorption on a core-single shell ZnNb catalyst

Morishita T., Ueno T., Panomsuwan G., Hieda J., Antoaneta Bratescu M., Saito N.

RSC Advances Vol. 6 ( 100 ) page： 98091 - 98095 2016

Language：English Publishing type：Research paper (scientific journal) Publisher：RSC Advances

Oxygen adsorption onto Pt, Nb, and core-single shell ZnNb particles is studied using ab initio molecular orbital (MO) calculations to realize their ability for the oxygen reduction reaction (ORR). The calculations demonstrate that the electronic state of oxygen adsorption on core-single shell ZnNb is very close to that on Pt, rather than that on Nb. The energy levels of the oxygen 2pσ∗ orbital and the antibonding orbital formed by the oxygen 2pπ∗ and metal d orbitals are different depending on the type of catalyst. In contrast, the energy level of the Nb-O π∗ (O2 2pπ∗ + Nb 4d antibonding) orbital of the core-single shell ZnNb is located at a position close to that of Pt. Our finding suggests that the oxygen adsorbed on the core-single shell ZnNb particle can easily be dissociated and desorbed owing to the disappearance of the interaction between the oxygen and Nb subsurface atoms through the replacement of Zn. We expect that core-single shell ZnNb can be utilized as an efficient and cost-effective catalyst for the ORR in a polymer electrolyte fuel cell.

DOI： 10.1039/c6ra19311k

Enhancement of conductivity in nano carbon balls by the addition of carbon tetrachloride: Via room temperature solution plasma process

Li O.L., Hayashi H., Ishizaki T., Saito N.

RSC Advances Vol. 6 ( 57 ) page： 51864 - 51870 2016

Language：English Publishing type：Research paper (scientific journal) Publisher：RSC Advances

The conductivity of carbon nanoballs (CNBs) was enhanced by two orders of magnitude with the addition of carbon tetrachloride through a room temperature solution plasma process without post-heat treatment. The synthesized CNBs demonstrated the lowest resistivity of 8 Ω cm when the ratio of benzene to carbon tetrachloride was adjusted to 3:2. The morphologies from Transmission Electron Microscopy (TEM) showed the benzene-synthesized CNBs appeared as amorphous carbon while CNBs generated from the mixture of carbon tetrachloride and benzene were presented as short range graphite with turbostratic structure. From Raman spectroscopy and X-ray diffraction patterns, the results indicated the transition from amorphous carbon to nanocrystalline-graphite (NCG). From chemical elemental analysis, the hydrogen mole percentage decreased 20-50% when 20-60 vol% of carbon tetrachloride was added into benzene. We expect that this approach can be extended to enhance the conductivity of all kinds of amorphous carbonaceous materials in other synthesis technologies under room temperature.

DOI： 10.1039/c6ra02453j

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