Faculty Profiles - SAITO, Nagahiro

Papers - SAITO, Nagahiro

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The plasma-assisted formation of Ag@Co<inf>3</inf>O<inf>4</inf> core-shell hybrid nanocrystals for oxygen reduction reaction

Kim S.M., Jo Y.G., Lee M.H., Saito N., Kim J.W., Lee S.Y.

Electrochimica Acta Vol. 233 page： 123 - 133 2017.4

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

In this study, Ag@Co3O4 core-shell hybrid nanocrystals are synthesized using a plasma discharge in water for oxygen reduction reaction in alkaline solutions. A detailed analysis via electron microscopy in combination with EDS elemental mapping conclusively verifies that the reactive oxygen species generated from the plasma-assisted decomposition of water molecules govern the phase structure of the nanocrystals. Under oxidizing conditions, the Co oxide, which is more stable than the Ag oxide, provides the driving force for the segregation and preferential oxidation of Co at the surface. This leads to the formation of the core-shell architecture. The electrochemical measurements for the oxygen reduction reaction reveal that the specific activities of the Ag@Co3O4 core-shell nanocrystals are ca. 5.2 and 2.6 times higher than those of the pure Ag and Ag-Co alloy nanocrystals. The enhanced catalytic performance is attributed to the combination of electronic and geometric effects, which facilitates the O[sbnd]O bond breaking and desorption for the oxygen reduction. The insights gain through this study may serve as a foundation to design better electrochemical oxygen reduction electrocatalysts.

DOI： 10.1016/j.electacta.2017.03.049

Enhanced ferromagnetism in graphite-like carbon layer-coated ZnO crystals

Tu N., Dung N.H., Lan N.T., Nguyen K.T., Dung N.D., Viet D.X., Tuan N.T., Bui H.V., Nam D.V., Huy P.T., Saito N.

Journal of Alloys and Compounds Vol. 695 page： 233 - 237 2017

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

We report on the preparation of graphite-like carbon-coated ZnO nanoparticles by ball milling a powder mixture of ZnO and C. Magnetic measurements indicated that carbon coating can strongly enhance the room-temperature ferromagnetism of ZnO nanoparticles, depending on preparation conditions. This enhancement may stem from robust ferromagnetism at the ZnO/C interface. The origin of interfacial ferromagnetism is attributed to crystallographic defects at the surface of ZnO crystals which are stabilized by the carbon shell layer.

DOI： 10.1016/j.jallcom.2016.10.200

Facile preparation of defective black TiO<inf>2</inf> through the solution plasma process: Effect of parametric changes for plasma discharge on its structural and optical properties

Jedsukontorn T., Ueno T., Saito N., Hunsom M.

Journal of Alloys and Compounds Vol. 726 page： 567 - 577 2017

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

Defective TiO2 or black TiO2 nanoparticles (NPs) are remarkably attractive for photocatalytic applications, since the defect-disordered structure crucially affects the optical properties. In this work, high visible light-active black TiO2 NPs were synthesized by an innovative solution plasma process (SPP) with a titanium (Ti) electrode in HNO3 solution. The effects of the plasma operating parameters, in terms of the pulse frequency (20–80 kHz) and pulse width (0.5–2.0 μs) under two different HNO3 concentrations (0.3 mM and 3.0 mM) on the morphology, structural and optical properties of the obtained black TiO2 NPs were explored. Increasing the pulse frequency, pulse width and concentration of HNO3 all increased the input energy per pulse and energy per second, which induced an increased volume-based particle size, synthesis rate and Ti3+/Ti4+ ratio, but decreased the rutile mass fraction, the Ti-OH/TiO ratio and the band gap energy of the obtained black TiO2 NPs. Among all the prepared black TiO2 NP samples, those prepared at a pulse frequency of 20 kHz, pulse width of 2 μs (energy input per second of 17.3 J) in 3.0 mM HNO3 exhibited the highest visible-light absorption capability (the lowest band gap energy of ∼2.44 eV). The variation in the band gap energy was more strongly dependent on the Ti3+/Ti4+ ratio than the Ti-OH/TiO ratio in the structure of black TiO2 NPs.

DOI： 10.1016/j.jallcom.2017.08.028

New insights into vegetable oil pyrolysis by cold plasma technique Open Access

Meeprasertsagool P., Watthanaphanit A., Ueno T., Saito N., Reubroycharoen P.

Energy Procedia Vol. 138 page： 1153 - 1158 2017

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

Green liquid fuels are alternatively produced by pyrolysis of vegetable oil. Still, this process requires high processing temperature and high energy consumption per unit cost. Recently, solution/liquid-phase plasma (cold plasma) is the novel method to provide the direct energy at highly excited energy state. In this study, the investigation of the green fuel synthesis from vegetables oils using cold plasma was examined. The cold plasma reactor was connected to a bipolar pulsed power supply under 200 ml of palm oil, the pulse frequency adjusted from 15-45 kHz and the voltage adjusted in ranges of 1.2-1.5 kV with 40 minutes of discharge times, pulse width 2 μs, electrode distance 0.5 mm. Properties of generated plasma were investigated by optical emission spectroscopy (OES) methods. The liquid products were analysed by GC-MS. In order to identify components of the liquid product, a GC-MS chromatogram was carried out; the main peaks were oleic acid and palmitic acid. Therefore, the other peak showed which products were cracked to short-chain hydrocarbon and hexadecane was one of the compounds which were cracked in palm oil. In conclusion, the results showed that plasma has potential and enough energy to convert vegetable oils in liquid fuels at room temperature which can also provide the direct energy better than pyrolysis.

DOI： 10.1016/j.egypro.2017.10.224

Photocatalytic behavior of metal-decorated TiO<inf>2</inf> and their catalytic activity for transformation of glycerol to value added compounds

Jedsukontorn T., Saito N., Hunsom M.

Molecular Catalysis Vol. 432 page： 160 - 171 2017

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

In this work, TiO2 was decorated with one of four different metals (Bi, Pd, Pt and Au) by sol immobilization at ambient condition. The individual addition of each metals on the TiO2 did not affect the crystallite size or band gap energy of TiO2, but increased its visible light absorption ability due to the localized surface plasmon resonance effect of the doped metals, except for Bi, as well as the mechanism of the charge transfer. Among all the prepared metal-decorated TiO2 photocatalysts, Au/TiO2 exhibited the highest visible light absorption ability and an appropriate mechanism of charge transfer, which consequently alleviated the e−–h+ recombination. It also provided the highest photocatalytic activity for glycerol conversion (92.8% at 14 h) and yield of dihydroxyacetone, glyceraldehyde, glycolic acid, hydroxypyruvic acid and formaldehyde of 12.0, 23.1, 10.7, 13.6 and 15.3%, respectively.

DOI： 10.1016/j.mcat.2017.02.022

Novel synthesis of PtPd nanoparticles with good electrocatalytic activity and durability

Zhang J., Hu X., Yang B., Su N., Huang H., Cheng J., Yang H., Saito N.

Journal of Alloys and Compounds Vol. 709 page： 588 - 595 2017

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

PtPd nanoparticles in the size range of 2–5 nm have been directly synthesized from their metal wire electrodes via a one-step plasma sputtering technique in a solution of water and methanol under atmospheric pressure. PtPd nanoparticles produced in the water/methanol solution have good dispersibility compared with those produced in water because methanol successfully reduces the aggregation of the nanoparticles during the plasma sputtering process. Further, the solution plasma technique provides a novel reaction field with a highly energetic state for the PtPd nanoparticle synthesis. KB-supported PtPd nanoparticles (PtPd/KB, 12 wt% Pt) exhibit excellent electrocatalytic activity (over 4 times mass activity compared with commercial Pt/C) and stability (maintaining 43% mass activity after 300 cycles) towards methanol electrooxidation because of their large electrochemical surface area (ECSA, that is 2.5 times greater than that of commercial Pt/C) and synergistic effect of the binary alloy. Thus, as-synthesized PtPd/KB catalysts may have potential applications in direct methanol fuel cells (DMFCs) to lower their cost and improve their cycle efficiency.

DOI： 10.1016/j.jallcom.2017.03.202

Simple introduction of carboxyl head group with alkyl spacer onto multiwalled carbon nanotubes by solution plasma process Open Access

Nemoto S., Ueno T., Watthanaphanit A., Hieda J., Bratescu M.A., Saito N.

Japanese Journal of Applied Physics Vol. 56 ( 9 ) 2017

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

A simple method of fabricating carboxyl-terminated multiwalled carbon nanotubes (MWCNTs) with alkyl spacers was developed to improve the dispersion quality of MWCNTs in aqueous solutions using solution plasma (SP) in a 6-aminocaproic acid solution. The formation of SP in the solution led to better dispersion of MWCNTs in aqueous solutions. Fourier transform infrared spectroscopy (FT-IR) results indicate that a carboxyl group with an alkyl spacer can be introduced by SP treatment in the 6-aminocaproic acid solution. Sedimentation tests show that the SP-treated MWCNTs in the 6-aminocaproic acid solution retained their good dispersion quality in aqueous solutions of pHs 5 6 and 9. The alkyl spacer plays an important role in the preservation of dispersion states particularly at pH 6.

DOI： 10.7567/JJAP.56.096202

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

Synthesis of carbon nanoparticles from used motor oil and benzene via solution plasma process

Seangarunthong N., Khongthong P., Panomsuwan G., Ueno T., Saito N., Eiad-Ua A.

Key Engineering Materials Vol. 751 KEM page： 773 - 778 2017

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

Carbon nanoparticles (CNPs) were successfully synthesized from the mixture of used motor oil and benzene via a solution plasma process (SPP). The synthesis was achieved within a single step at room temperature and atmospheric pressure. The effects of mixing ratio between used motor oil and benzene on the physical and chemical properties of CNPs were investigated by means of field-emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and Raman spectroscopy. The results revealed that there were no significant changes in morphological feature and chemical functional groups on CNPs at different mixing ratios. The CNPs exhibited the aggregates of fine particles with the diameter of about 20-30 nm. The crystallinity of CNPs was found to be slightly increased when synthesized under the presence of used motor oil, possibly due to the effect of aliphatic hydrocarbons and polycyclic aromatic hydrocarbons in used motor oil. We expect that the conversion of used motor oil into CNPs by SPP could be another attractive way to add the value to used motor oil prior to disposing.

DOI： 10.4028/www.scientific.net/KEM.751.773

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

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 Open Access

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.

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