Faculty Profiles - SAITO, Nagahiro

Papers - SAITO, Nagahiro

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Effect of treatment time in the Mg(OH)<inf>2</inf>/Mg–Al LDH composite film formed on Mg alloy AZ31 by steam coating on the corrosion resistance

Kamiyama N., Panomsuwan G., Yamamoto E., Sudare T., Saito N., Ishizaki T.

Surface and Coatings Technology Vol. 286 page： 172 - 177 2016

Language：English Publishing type：Research paper (scientific journal) Publisher：Surface and Coatings Technology

The corrosion resistant films were fabricated on Mg alloy AZ31 substrates by steam coating method using Al(NO3)3·9H2O aqueous solution as a steam source. The treatment temperature was maintained at 433 K, while the treatment time was varied at 3, 5, 7 and 9 h. X-ray diffraction (XRD) analysis demonstrated that the coated films were composed of a mixed structure of Mg(OH)2 and Mg–Al layered double hydroxide (Mg–Al LDH) phases. As revealed by the scanning electron microscopy (SEM) observation, the surface of coated films had a good uniformity of changing treatment times. The deposition rate increased exponentially with increasing treatment time. Fourier transform infrared (FT-IR) spectra showed that carbonate and nitrate ions were co-existed in the interlayer of Mg–Al LDH. The potentiodynamic polarization curves of the film coated for 7 h exhibited the lowest corrosion current density, which was almost four orders of magnitude lower than that of bare AZ31. The enhanced corrosion resistance was well consistent with the increase of Mg–Al LDH content in the films.

DOI： 10.1016/j.surfcoat.2015.11.051

Effect of microstructure on corrosion resistance and heat resistance of flame-resistant Ca-added magnesium alloy AZ61

Serizawa A., Iwase Y., Sudare T., Saito N., Kamiyama N., Ishizaki T.

Keikinzoku/Journal of Japan Institute of Light Metals Vol. 66 ( 1 ) page： 9 - 14 2016

Language：English Publishing type：Research paper (scientific journal) Publisher：Keikinzoku/Journal of Japan Institute of Light Metals

Effect of microstructure on corrosion resistance and heat resistance of flame-resistant Ca-added magnesium alloy AZ61 (AZX612) were investigated. An extruded and twin-rolled casting magnesium alloys AZX612 were used with a view to better understanding the relationship between microstructure and these properties. The microstructures of the magnesium alloys were characterized by optical microscope (OM), X-ray diffraction (XRD) and scanning electron microscopy (SEM)/energy dispersive X-ray spectroscopy (EDS). The shapes of compounds in the alloys observed by EDS were significantly different; spherical distribution in grain for the extruded magnesium alloy and preferential formation on grain boundaries for the twin-rolled casting magnesium alloy. The different microstructure of the two alloys resulted in showing the different properties. Immersion test in 5 mass% NaCl aqueous solution revealed that the corrosion rates for the extruded and twin-rolled casting magnesium alloys AZX612 were estimated to be 6.5 and 15.0 mm/year, respectively, indicating that the corrosion resistance of the extruded magnesium alloys AZX612 were more superior than that of the twin-rolled casting one. On the contrary, the heat resistance of the alloy did not change depending on the microstructure.

DOI： 10.2464/jilm.66.9

Fe-N-doped carbon-based composite as an efficient and durable electrocatalyst for the oxygen reduction reaction

Panomsuwan G., Saito N., Ishizaki T.

RSC Advances Vol. 6 ( 115 ) page： 114553 - 114559 2016

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

We herein report the preparation of an Fe-N-doped carbon nanoparticle-carbon nanofiber (Fe-N-CNP-CNF) composite using a solution plasma process followed by heat treatment. The resulting Fe-N-CNP-CNF exhibits excellent catalytic activity, durability, and methanol tolerance for the oxygen reduction reaction (ORR) in an alkaline solution. The enhanced ORR activity of Fe-N-CNP-CNF can reasonably be attributed to the synergistic contributions provided by a high degree of graphitization of CNF, meso/macroporosity of CNP, presence of catalytically active sites for ORR (i.e., graphitic N and Fe-N bond), and existence of carbon-encapsulated Fe/Fe3C particles.

DOI： 10.1039/C6RA24214F

Synthesis of colloidal MnO<inf>2</inf> with a sheet-like structure by one-pot plasma discharge in permanganate aqueous solution

Kim H., Watthanaphanit A., Saito N.

RSC Advances Vol. 6 ( 4 ) page： 2826 - 2834 2016

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

Stable colloidal MnO2 - consisting of MnO2 with a sheet-like structure - was synthesized by solution plasma process (SPP). The synthesis was completed in one-step by discharging the plasma in potassium permanganate (KMnO4) aqueous solution without using any dispersants or stabilizers. An alteration of the manganese oxide oxidation state, from MnO4- to MnO2 as a function of the discharge time, was investigated by UV-vis spectroscopy. Morphology and elemental constituents were observed by TEM and EDS mapping. Results indicated that the discharge time was an important feature for the formation of MnO2 in the SPP system. Specifically at neutral pH (pH = 7), MnO4- was completely reduced to MnO2 within a discharge time of 18 min. After that the obtained MnO2 was converted rapidly to Mn2+. To better understand the possible pathways of MnO2 formation by the SPP, we compared aspects of the reaction under different pH conditions. Formation of MnO2 under additional, controlled pH conditions, i.e. 2 and 12, was studied. Results suggested that hydrogen species played a key role for the reduction of MnO4- in the water-based SPP system. In comparison to the existing routes for the synthesis of MnO2 nanosheets with a single or low number of layers, the SPP holds excellent promise as an effective alternative means regarding its simplicity, time-energy preserving, and scalability.

DOI： 10.1039/c5ra20416j

Synthesis of heteroatom-carbon nanosheets by solution plasma processing using: N -methyl-2-pyrrolidone as precursor

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

RSC Advances Vol. 6 ( 9 ) page： 6990 - 6996 2016

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

Nitrogen-carbon nanosheets (NCNS), composed of multi-layer graphene with turbostratic stacking, were successfully synthesized through a solution plasma processing (SPP) at room temperature and an atmospheric pressure. The plasma was generated in 200 mL of N-methyl-2-pyrrolidone (NMP), which was applied as the carbon and nitrogen precursors. The NCNS presented an electrical resistivity of 0.065 Ω cm, which is comparable with that of N-doped carbon nanofibers (CNFs) and N-doped carbon nanotubes (CNTs). The synthesis rate of NCNS was 20 mg min-1. From the characteristics analyses, NCNS showed the surface area of 277 m2 g-1, a pore volume of 0.95 cm3 g-1 and a moderate nitrogen content of 1.3 at%. The synthesized NCNS also exhibited catalytic activity towards oxygen reduction reaction (ORR). This unique synthesis method can be applicable to synthesize multiple types of heteroatom-carbon nanosheets.

DOI： 10.1039/c5ra23659b

Verification of Radicals Formation in Ethanol-Water Mixture Based Solution Plasma and Their Relation to the Rate of Reaction

Sudare T., Ueno T., Watthanaphanit A., Saito N.

Journal of Physical Chemistry A Vol. 119 ( 48 ) page： 11668 - 11673 2015.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Physical Chemistry A

Our previous research demonstrated that using ethanol-water mixture as a liquid medium for the synthesis of gold nanoparticles by the solution plasma process (SPP) could lead to an increment of the reaction rate of ∼35.2 times faster than that in pure water. This drastic change was observed when a small amount of ethanol, that is, at an ethanol mole fraction (χethanol) of 0.089, was added in the system. After this composition, the reaction rate decreased continuously. To better understand what happens in the ethanol-water mixture-based SPP, in this study, effect of the ethanol content on the radical formation in the system was verified. We focused on detecting the magnetic resonance of electronic spins using electron spin resonance spectroscopy to determine the type and quantity of the generated radicals at each χethanol. Results indicated that ethanol radicals were generated in the ethanol-water mixtures and exhibited maximum quantity at the xethanol of 0.089. Relationship between the ethanol radical yield and the rate of reaction, along with possible mechanism responsible for the observed phenomenon, is discussed in this paper.

DOI： 10.1021/acs.jpca.5b07224

Adsorption and desorption of DNA tuned by hydroxyl groups in graphite oxides-based solid extraction material

Akceoglu G., Li O., Saito N.

Colloids and Surfaces B: Biointerfaces Vol. 136 page： 1 - 6 2015.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Colloids and Surfaces B: Biointerfaces

The extraction of DNA is the most crucial method used in molecular biology. Up to date silica matrices has been widely applied as solid support for selective DNA adsorption and extraction. However, since adsorption force of Si. OH functional groups is much greater than that of desorption force, the DNA extraction efficiency of silica surfaces is limited. In order to increase the DNA extraction yield, a new surface with different functional groups which possess of greater desorption property is required. In this study, we proposed cellulose/graphite oxide (GO) composite as an alternative material for DNA adsorption and extraction. GO/Cellulose composite provides the major adsorption and desorption of DNA by C. OH, which belongs to alkyl or phenol type of OH functional group. Compared to Si. OH, C. OH is less polarized and reactive, therefore the composite might provide a higher desorption of DNA during the elution process. The GO/cellulose composite were prepared in spherical structure by mixing urea, cellulose, NaOH, Graphite oxide and water. The concentration of GO within the composites were controlled to be 0-4.15. wt.%. The extraction yield of DNA increased with increasing weight percentage of GO. The highest yield was achieved at 4.15. wt.% GO, where the extraction efficiency was reported as 660.4. ng/μl when applying 2. M GuHCl as the binding buffer. The absorbance ratios between 260. nm and 280. nm (A260/A280) of the DNA elution was demonstrated as 1.86, indicating the extracted DNA consisted of high purity. The results proved that GO/cellulose composite provides a simple method for selective DNA extraction with high extraction efficiency of pure DNA.

DOI： 10.1016/j.colsurfb.2015.07.080

Influences of solution plasma conditions on degradation rate and properties of chitosan

Tantiplapol T., Singsawat Y., Narongsil N., Damrongsakkul S., Saito N., Prasertsung I.

Innovative Food Science and Emerging Technologies Vol. 32 page： 116 - 120 2015.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Innovative Food Science and Emerging Technologies

In this work, the effects of solution plasma conditions on the degradation rate and properties of chitosan are investigated. Various types of electrodes including tungsten (W), copper (Cu), and iron (Fe) were used. The treatment time and the applied pulse frequency of the bipolar supply varied from 0 to 210 min and 15 to 30 kHz, respectively. The plasma-treated chitosan was characterized by GPC, XRD, FT-IR, and fractionation analysis. The results showed that after plasma treatment for 210 min, the molecular weight of chitosan decreased remarkably, when compared to those of untreated samples. The plasma treatment of chitosan using Fe electrode and high pulse frequency strongly promoted the degradation rate of chitosan. The XRD analysis showed that the crystallinity of plasma-treated chitosan was destroyed. FT-IR analysis revealed that the chemical structure of chitosan was not changed by solution plasma treatment. Solution plasma treatment of chitosan using an Fe electrode provided the highest %yield of water-soluble chitosan. Industrial Relevance In this study, the solution plasma process is introduced to treat chitosan in order to prepare low-molecular-weight chitosan. According to our finding, the solution plasma could be a potential method for the preparation of low-molecular-weight chitosan and chitooligosaccharides. Since the solution plasma is generated under mild conditions (i.e.; the reaction proceeds at room temperature and ambient pressure), therefore, it is very attractive for the degradation of polysaccharide polymer and applicable to industrial materials process such as medicine, food, chemical industry, and cosmetics. In addition, we expected that plasma technology could be used instead of conventional enzymatic treatment and chemical treatment which was high cost and contamination process.

DOI： 10.1016/j.ifset.2015.09.014

Route of glycerol conversion and product generation via TiO<inf>2</inf>-induced photocatalytic oxidation in the presence of H<inf>2</inf>O<inf>2</inf>

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

Chemical Engineering Journal Vol. 281 page： 252 - 264 2015.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Chemical Engineering Journal

The objective of this study was to explore the route of glycerol conversion and product generation via the TiO2-induced photocatalytic oxidation in the presence of H2O2. Effects of TiO2 dosage (1-3g/L), H2O2 concentration (0.3-1.5M), light UV intensity (1.1-4.7mW/cm2) and irradiation time (4-8h) on the level of glycerol conversion and product selectivity were identified using a 2k factorial design. It was found that TiO2 and H2O2 played a simultaneous positive effect on the glycerol conversion in the presence of UV-light. Among all investigated parameters, the most important parameter on glycerol conversion and product selectivity was the irradiation time. Glycerol conversion and product generation can proceed via both h+-mediate and radical-mediated routes, but the radical-mediated route was dominant.

DOI： 10.1016/j.cej.2015.06.078

Accelerated nanoparticles synthesis in alcohol-water-mixture-based solution plasma

Sudare T., Ueno T., Watthanaphanit A., Saito N.

Physical Chemistry Chemical Physics Vol. 17 ( 45 ) page： 30255 - 30259 2015.10

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

An extraordinary high-speed synthesis of gold nanoparticles (AuNPs) was discovered by synthesizing the AuNPs in ethanol-water mixtures using a solution plasma process (SPP). The influence of the ethanol mole fraction (χethanol) in the ethanol-water mixtures on the reduction rate of gold chloride ions to AuNPs under the SPP system was studied. The results indicated that the reaction rate of the AuNPs synthesis exhibited a maximum value (i.e. 35.2 times faster than in a pure water system) at the significant point where the partial molar volumes of ethanol and water changed drastically.

DOI： 10.1039/c5cp05168a

The Effect of Electrode Gap Distance on the Synthesis of Carbon Materials by Using Solution Plasma Process

Lee H., Ueno T., Saito N.

JOM Vol. 67 ( 11 ) page： 2550 - 2556 2015.10

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

Carbon nanomaterials were synthesized by using the solution plasma process and the carbon structure was precisely controlled through adjusting electrode gap distances. Transmission electron microscope and diffraction images showed ordered graphitic layers and clear ring patterns when the electrode distance was wider. The measurement of conductive properties has been improved approximately 400 times from 19 k Ω cm to 47 Ω cm, and the C/H ratio from the result of elemental analysis decreased from 0.31 to 0.18 with decreasing resistivity of carbon. These results showed that the electrode distance was an important factor to control the energy input during the synthesis of carbon materials in the plasma/gas zone generated by solution plasma processing and strongly affect the properties of synthesized carbon materials.

DOI： 10.1007/s11837-015-1660-9

Innovative Graphite Oxide-Cellulose Based Material Specific for Genomic DNA Extraction

Akceoglu G.A., Li O.L., Saito N.

JOM Vol. 67 ( 11 ) page： 2557 - 2563 2015.9

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

Extraction of genomic DNA from various types of samples is often challenging for commercial silica spin column. In this study, we proposed graphite oxide (GO)/cellulose composite as an alternative material for genomic DNA extraction. The purity of DNA and extraction efficiency were compared to that of commercial silica product. In this study, the total weight % of GO was fixed at 4.15% in GO/Cellulose composite. Chewed gum, nail clip, cigarette bud paper, animal tissue and hair sample were used as various genomic DNA sources for extraction experiments. Among all types of samples, the extraction efficiencies were 4 to 12 times higher than that of commercial silica spin column. The absorbance ratio of 260 nm to 280 nm (A260/A280) of all samples ranged between 1.6 and 2.0. The results demonstrated that GO/Cellulose composites might serve as an innovative solid support material for genomic DNA extraction.

DOI： 10.1007/s11837-015-1610-6

Electrocatalytic oxygen reduction activity of boron-doped carbon nanoparticles synthesized via solution plasma process

Panomsuwan G., Saito N., Ishizaki T.

Electrochemistry Communications Vol. 59 page： 81 - 85 2015.7

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

The synthesis of boron-doped carbon nanoparticles (BCNP) has been achieved through a solution plasma process without the addition of a metal catalyst source using a mixture of benzene and triphenyl borate as precursor. The electrocatalytic activity toward the oxygen reduction reaction (ORR) of BCNP can be improved in terms of onset potential and current density compared to that of undoped carbon nanoparticles in alkaline solution. Moreover, BCNP possesses superior long-term durability and tolerance to methanol oxidation in the ORR.

DOI： 10.1016/j.elecom.2015.07.005

Thermal plasma treatment of stormwater sediments: Comparison between DC non-transferred and partially transferred arc plasma

Li O.L., Guo Y., Chang J.S., Saito N.

Environmental Technology (United Kingdom) Vol. 36 ( 13 ) page： 1672 - 1679 2015.7

Language：English Publishing type：Research paper (scientific journal) Publisher：Environmental Technology (United Kingdom)

The disposal of enormous amount of stormwater sediments becomes an emerging worldwide problem. Stormwater sediments are contaminated by heavy metals, phosphorus, trace organic and hydrocarbons, and cannot be disposed without treatment. Thermal plasma decontamination technology offers a high decomposition rate in a wide range of toxic organic compound and immobilization of heavy metal. In this study, we compared the treatment results between two different modes of thermal plasma: (1) a non-transferred direct current (DC) mode and (2) a partial DC-transferred mode. The reductions of total organic carbon (TOC) were, respectively, 25% and 80% for non-transferred and partially transferred plasma, respectively. Most of the toxic organic compounds were converted majorly to CxHy. In the gaseous emission, the accumulated CxHy, CO, NO and H2S were significantly higher in partially transferred mode than in non-transferred mode. The solid analysis demonstrated that the concentrations of Ca and Fe were enriched by 500% and 40%, respectively. New chemical compositions such as KAlSi3O8, Fe3O4, NaCl and CaSO4 were formed after treatment in partially DC-transferred mode. The power inputs were 1 and 10 kW, respectively, for non-transferred DC mode and a partially DC-transferred mode. With a lower energy input, non-transferred plasma treatment can be used for decontamination of sediments with low TOC and metal concentration. Meanwhile, partially transferred thermal plasma with higher energy input is suitable for treating sediments with high TOC percentage and volatile metal concentration. The organic compounds are converted into valuable gaseous products which can be recycled as an energy source.

DOI： 10.1080/09593330.2014.1003981

Water-plasma-assisted synthesis of black titania spheres with efficient visible-light photocatalytic activity

Panomsuwan G., Watthanaphanit A., Ishizaki T., Saito N.

Physical Chemistry Chemical Physics Vol. 17 ( 21 ) page： 13794 - 13799 2015.6

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

Black titania spheres (H-TiO<inf>2-x</inf>) were synthesized via a simple green method assisted by water plasma at a low temperature and atmospheric pressure. The in situ production of highly energetic hydroxyl and hydrogen species from water plasma are the prominent factors in the oxidation and hydrogenation reactions during the formation of H-TiO<inf>2-x</inf>, respectively. The visible-light photocatalytic activity toward the dye degradation of H-TiO<inf>2-x</inf> can be attributed to the synergistic effect of large-surface area, visible-light absorption and the existence of oxygen vacancies and Ti<sup>3+</sup> sites.

DOI： 10.1039/c5cp00171d

Simple one-step synthesis of fluorine-doped carbon nanoparticles as potential alternative metal-free electrocatalysts for oxygen reduction reaction

Panomsuwan G., Saito N., Ishizaki T.

Journal of Materials Chemistry A Vol. 3 ( 18 ) page： 9972 - 9981A 2015.5

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

Fluorine-doped carbon nanoparticles (FCNPs) were synthesized via a simple one-step solution plasma process for the first time. This synthesis strategy can be achieved at relatively low temperature and atmospheric pressure without the involvement of a metal catalyst. A mixture of toluene (C<inf>6</inf>H<inf>5</inf>CH<inf>3</inf>) and trifluorotoluene (C<inf>6</inf>H<inf>5</inf>CF<inf>3</inf>) was used as a precursor for the synthesis. The fluorine doping content can be varied from 0.95 to 4.52 at%, depending on the precursor mixing ratio. The structural analyses reveal that FCNPs mainly exhibit a disordered amorphous structure. The incorporation of fluorine atoms results in the creation of more defect sites and disordered structure in the carbon particles. The electrocatalytic activity toward the oxygen reduction reaction (ORR) of FCNPs in an alkaline solution shows a significant improvement with increasing fluorine doping content, as reflected in an increased limiting current density and a positively shifted onset potential. In association with X-ray photoelectron spectroscopy (XPS) analysis, an improved ORR activity is possibly attributed to the intercalation of ionic C-F and semi-ionic C-F bonds in the carbon structure. In addition, FCNPs possess excellent long-term operation durability and strong tolerance to methanol oxidation compared to those of a commercial Pt-based catalyst. Our results from this study not only confirm the applicability of the solution plasma process to the synthesis of FCNPs with a controllable fluorine doping level but also provide detailed information of FCNPs as potential alternative ORR catalysts for the electrocatalysis research.

DOI： 10.1039/c5ta00244c

A new approach of nonpoint source pollution/stormwater sludge treatment by an integrated thermal plasma system

Li O.L., Guo Y., Chang J.S., Urashima K., Saito N.

International Journal of Environmental Science and Technology Vol. 12 ( 5 ) page： 1769 - 1778 2015.5

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

In this study, we designed and demonstrated the effectiveness of an integrated waste treatment system for contaminated stormwater sludge. The system is comprised of two components: pulsed arc electrohydraulic discharge (PAED) for aqueous-phase treatment and thermal plasma decontamination for solid-phase treatment. PAED provided a reduction of 80 % in total organic carbon (TOC) within a treatment time of 5 min in the aqueous phase. With a prolonged treatment of 30 min, the decontamination of TOC reached over 90 % in the aqueous phase, accompanied with 20 % carbon and 70 % sulfur decreases in weight in the solid phase. A huge weight reduction can be achieved prior to further solid treatment. The solid phase, named as the PAED-treated sludge, was separated by sedimentation and transferred to thermal plasma treatment. The thermal plasma-treated sludge was slightly melted, and the formation of slag was possible. X-ray energy dispersion solid analysis showed that carbon and sulfur were reduced to zero after treatment. Si, Mg, and Al decreased by 25, 30, and 60 %, respectively, while Ca and Fe enriched by 400 and 25 %, respectively. The emission gas analyses demonstrated a possible energy recovery from gaseous compounds with adequate gaseous treatment devices. This research demonstrates an innovative treatment approach of various sludge types, especially those types that contain high water contents and are severely contaminated by toxic organic compounds.

DOI： 10.1007/s13762-014-0570-7

Nitrogen-doped carbon nanoparticles derived from acrylonitrile plasma for electrochemical oxygen reduction

Panomsuwan G., Saito N., Ishizaki T.

Physical Chemistry Chemical Physics Vol. 17 ( 9 ) page： 6227 - 6232 2015.3

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

Nitrogen-doped carbon nanoparticles were synthesized via a solution plasma process, with acrylonitrile as a single-source precursor, followed by a post-thermal annealing process. The nitrogen-bonding states can be tuned by varying the annealing temperature. The best electrocatalytic activity for oxygen reduction reaction (ORR) in terms of both onset potential and limiting current density can be achieved for the catalyst annealed at an optimal temperature of 800 °C because of the high content of graphitic-N catalytic sites and a large specific surface area.

DOI： 10.1039/c4cp05995f

One-step facile synthesis of carbon-supported PdAu nanoparticles and their electrochemical property and stability

Hu X., Shi J., Zhang J., Tang W., Zhu H., Shen X., Saito N.

Journal of Alloys and Compounds Vol. 619 page： 452 - 457 2015.1

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

Well-crystallized PdAu nanoparticles supported on Ketjen Black (KB) were successfully fabricated when both Pd and Au wires were served as the electrode pair by a solution plasma technique at atmospheric pressure. The synthesis of PdAu nanoparticles was almost simultaneous with their dispersion on KB. As-obtained PdAu nanoparticles were confirmed to be alloy by ultraviolet-visible spectrophotometer, transmission electron microscopy (TEM) and energy dispersive X-ray analysis (EDX) of each particle. PdAu nanoparticles with the average diameter of 2-5 nm were equably distributed on KB. PdAu nanoparticles showed good electrocatalytic activity both in acidic and alkaline solution corresponding to their obvious oxidation and reduction features. PdAu nanoparticles have improved electrochemical stability compared with the electrochemical properties of Pd and Au nanoparticles mixture after long time multi-scan cyclic voltammetry. Multi-scan cyclic voltammetry also presented the PdAu nanoparticles in alkaline solution have better stability than that in acidic solution. Thus as-obtained PdAu alloy nanoparticles would become a promising electrocatalysts for fuel cells or Li-air batteries. This novel process showed its potential applications in designing optimization of catalysts for fuel cells or Li-air batteries in future.

DOI： 10.1016/j.jallcom.2014.09.051

Enhancement of ORR catalytic activity by multiple heteroatom-doped carbon materials

Kim D., Li O., Saito N.

Physical Chemistry Chemical Physics Vol. 17 ( 1 ) page： 407 - 413 2015.1

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

Heteroatom-doped carbon matrices have been attracting significant attention due to their superior electrochemical stability, light weight and low cost. Hence, in this study, various types of heteroatom, including single dopants of N, B and P and multiple dopants of B-N and P-N with a carbon matrix were synthesized by an innovative method named the solution plasma process. The heteroatom was doped into the carbon matrix during the discharge process by continuous dissociation and recombination of precursors. The chemical bonding structure, ORR activity and electrochemical performance were compared in detail for each single dopant and multiple dopants. According to the Raman spectra, the carbon structures were deformed by the doped heteroatoms in the carbon matrix. In comparison with N-doped structures (NCNS), the ORR potential of PN-doped structures (PNCNS) was positively shifted from -0.27 V to -0.24 V. It was observed that doping with N decreased the bonding between P and C in the matrix. The multiple doping induced additional active sites for ORR which further enhanced ORR activity and stability. Therefore, PNCNS is a promising metal-free catalyst for ORR at the cathode in a fuel cell.

DOI： 10.1039/c4cp03868a

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