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Yamamoto T.A.,Osaka University | Kageyama S.,Osaka University | Seino S.,Osaka University | Nitani H.,High Energy Accelerator Research Organization | And 5 more authors.
Applied Catalysis A: General | Year: 2011

Nanoparticle catalysts of PtRu/C for the direct methanol fuel cell anode were synthesized by a radiolytic process. Bimetallic substructures were controlled by varying irradiation dose rate and by addition of NH4OH or NaH2PO2. Material characterization was performed with the transmission electron microscopy, the X-ray diffraction, the X-ray fluorescence spectroscopy and the X-ray absorption fine structure techniques. Methanol oxidation activity was evaluated by the linear sweep voltammetry. We concluded that the structure of the radiolytically synthesized catalysts has a Pt-rich core/Ru-rich shell structure or incomplete alloy structure. A correlation between the substructures and catalytic activities was found by using a pairing factor defined from coordination numbers determined by the extend X-ray absorption fine structure analysis, which indicates the validity of the bifunctional mechanism in the PtRu nanoparticle system. This radiolytic process is promising for synthesizing advanced PtRu/C catalysts with well-mixed bimetallic substructures enhancing methanol oxidation. © 2011 Elsevier B.V. All rights reserved.


Ohkubo Y.,Osaka University | Kageyama S.,Osaka University | Seino S.,Osaka University | Nakagawa T.,Osaka University | And 3 more authors.
Journal of Experimental Nanoscience | Year: 2016

An electron-beam irradiation reduction method (EBIRM) is a technique to reduce metal ions in an aqueous solution via irradiation with a high-energy electron beam. In this study, an EBIRM is improved to develop a technique for the mass production of highly loaded and highly dispersed PtRu/C catalysts for use as direct methanol fuel cell anodes. An increase in the Pt and Ru input concentrations increased the loading weight from 9 to 37 wt%; however, the dispersibility of the PtRu nanoparticles on the carbon particles decreased. To improve the low dispersibility, sodium phosphinate was added to the precursor solution and the input amount of carbon particles was decreased. These changes resulted in not only highly loaded but also highly dispersed PtRu/C catalysts. The catalytic activity of the highly loaded and highly dispersed PtRu/C catalysts for methanol oxidation was at least 1.6 times higher than that of the lowly loaded and lowly dispersed PtRu/C catalysts in all voltage range. More than 6000 mg of highly loaded and highly dispersed PtRu/C catalysts were relatively easily obtained, and the average particle size of the PtRu nanoparticles was 1.8 nm. These results demonstrated that the improved EBIRM is effective for the mass production of carbon-supported, highly loaded, and highly dispersed metal nanoparticles. © 2015 Taylor & Francis.


Kageyama S.,Osaka University | Seino S.,Osaka University | Nakagawa T.,Osaka University | Nitani H.,High Energy Accelerator Research Organization | And 4 more authors.
Journal of Nanoparticle Research | Year: 2011

PtRu nanoparticle catalysts with 2-nm size supported on carbon were synthesized by a radiolytic process, assisted with the addition of dl-tartaric acid. Gradual alloying with the addition was confirmed by structural analyses with techniques of the X-ray diffraction and the X-ray absorption fine structure. Their methanol oxidation activities evaluated by the linear sweep voltammetry were higher than that of the commercial one, and found to be enhanced in accordance with the gradual change in the bimetallic structure from the Pt-core/Ru-shell to the random alloy. A good correlation was found between the catalytic activity and the indicators, which stands for the occurring frequency of the Pt-Ru bonds, calculated from the coordination numbers determined by the extended X-ray absorption fine structure analysis. It was confirmed that the addition of dl-tartaric acid in the radiolytic process certainly promoted the random alloy formation of PtRu bimetallic nanoparticles and enhanced their methanol oxidation activity. © 2011 Springer Science+Business Media B.V.


Ohkubo Y.,Osaka University | Seino S.,Osaka University | Nakagawa T.,Osaka University | Kugai J.,Osaka University | And 2 more authors.
Thin Solid Films | Year: 2016

A novel method for preparing thin Au films directly on resin substrates using an electron beam was developed. The thin Au films were prepared on a resin substrate by the reduction of Au ions in an aqueous solution via irradiation with a high-energy electron beam (4.8 MeV). This reduction method required 7 s of the irradiation time of the electron beam. Furthermore, no reductant or catalyst was needed. As the concentration of Au ions in the precursor solution was increased, the amount of Au deposited on the resin substrate increased, too, and the structure of the prepared Au film changed. As a result, the film color changed as well. Cross-sectional scanning electron microscope images of the thus-prepared Au film indicated that the Au films were consisted of two layers: a particle layer and a bottom bulk layer. There was strong adhesion between the Au films and the underlying resin substrates. This was confirmed by the tape-peeling test and through ultrasonic cleaning. After both processes, Au remained on the resin substrates, while most of the particle-like moieties were removed. This indicated that the thin Au films prepared via irradiation with a high-energy electron beam adhered strongly to the resin substrates. © 2016 Elsevier B.V. All rights reserved.


Nakamura S.,University of Shiga Prefecture | Nakamura S.,Hitachi Ltd. | Tokumitsu K.,University of Shiga Prefecture | Yamaguchi T.,Japan Electronic Beam Irradiation Service Co.
Journal of Applied Polymer Science | Year: 2013

This article investigates the effects of electron beam irradiation on the mechanical and thermal properties of polypropylene/polyamide6 blends (45/55) with talc 20% (w/w) as filler, SEBS-g-MAH 5% (w/w) as compatibilizer, and 10 phr triallyl isocyanurate (TAIC). TAIC is a polyfunctional monomer and acts as a crosslinking agent. Although the tensile and flexural moduli and strengths of the PP/PA6 blends with talc, SEBS-g-MAH, and TAIC were increased by the application of electron beam irradiation, the impact strength was decreased. Differential scanning calorimetry measurements showed that the melting temperatures and the degree of crystallinity decreased for all PP/PA6 blends as the electron beam irradiation dose increased, because of the number of structural defects in each crystalline phase. From dynamic mechanical analyzer results, a storage modulus curve in the plateau region was observed only in the PP/PA6 blends with talc, SEBS-g-MAH, and TAIC. The modulus increased with increasing electron beam irradiation dose, indicating that the three-dimensional network developed gradually in the more amorphous PA6. Consequently, the most significant improvement to heat distortion under high load (1.8 MPa) was observed at 200 kGy. Copyright © 2013 Wiley Periodicals, Inc.


Ohkubo Y.,Osaka University | Seino S.,Osaka University | Nakagawa T.,Osaka University | Ueno K.,Japan Electronic Beam Irradiation Service Ltd. | Yamamoto T.A.,Osaka University
Journal of Experimental Nanoscience | Year: 2016

To clarify the influence of pH on performance of sodium phosphinate (NaPH2O2) for decreasing particle size of Pt nanoparticles, carbon-supported Pt nanoparticles that contained phosphorus (P–Pt/C) were synthesised by an electron-beam irradiation reduction method (EBIRM) under four different pH conditions (pH = 3, 6, 9, and 12) and under five different NaPH2O2 concentrations (0.0, 0.5, 1.0, 3.0, and 5.0 mM). The relationship among pH, NaPH2O2 concentration, average particle size of Pt nanoparticle, and Pt loading weight was investigated in this study. The average particle size of Pt nanoparticles was in the range of 0.8–3.4 nm and lower in the order; pH12 > pH3 > pH6 > pH9; for example, under the same NaPH2O2 concentrations of 3.0 mM, the particle size of P–Pt/C prepared at pH = 12 and pH = 9 was 1.5 and 0.8 nm, respectively. In addition, Pt loading weight was also lower in the order; pH12 > pH3 > pH6 > pH9. In summary, these results indicated that the pH in the precursor solution affected the performance of NaPH2O2. These findings would be useful for controlling the particle size of monometallic Pt and Pt-based bimetallic nanoparticles supported on carbon particles for fuel cell applications. © 2016 Taylor & Francis


Kugai J.,Osaka University | Moriya T.,Osaka University | Seino S.,Osaka University | Nakagawa T.,Osaka University | And 4 more authors.
Journal of Physical Chemistry C | Year: 2013

The structure of bimetallic nanoparticles has a great impact on catalytic performance. By radiation-induced reduction of metal ions in the aqueous phase, supported bimetallic Pt-Cu catalysts were synthesized with various Cu loadings, support materials, and copper sources. These parameters had a great impact on the structural properties of Pt-Cu nanoparticles. On carbon black, Pt-Cu alloy nanoparticles were readily formed with little oxide phase. On CeO2 support, Pt-Cu was highly oxidized for the low-Cu region (Cu/Pt < 1), and Pt-Cu alloy nanoparticles were formed together with CuOx for the high-Cu region (Cu/Pt > 1). The structure of CeO2-supported catalysts obtained from two different copper sources (CuSO4 and CuCl2) suggested that such a drastic change in oxidation state is the result of two competing effects, CeO2 to oxygenate metals and the sulfate ion to stabilize them in the metallic state. The reaction characteristics in preferential CO oxidation reflected the Pt-Cu structure (oxidation state) determined by those parameters in the synthesis stage. The low-Cu oxidic samples showed excellent light-off performance, which was attributed to high oxygen transport from CeO2 to metals through the metal-CeO2 interface. The high-Cu samples comprising a Pt-Cu alloy and CuOx showed excellent selectivity, which was attributed to the metal-CuOx interface predominating over metal-CeO2. The latter exhibited 100% CO conversion in a wide temperature range in excess O 2 conditions. © 2013 American Chemical Society.


Ohkubo Y.,Osaka University | Seino S.,Osaka University | Kageyama S.,Osaka University | Kugai J.,Osaka University | And 3 more authors.
Journal of Nanoparticle Research | Year: 2014

Carbon-supported Pt nanoparticles that contained phosphorus (P-Pt/C) were synthesized by the reduction of Pt ions in an aqueous solution via irradiation with a high-energy electron beam; this synthesis technique is referred to as the electron beam irradiation reduction method (EBIRM). To decrease the size of the Pt nanoparticles supported on the carbon particles, sodium phosphinate (NaPH2O2) was added as a phosphorus precursor to the precursor solution that contained Pt ions. The P-Pt/C samples were observed using a transmission electron microscope. The average particle size of the Pt nanoparticles decreased as the NaPH2O2 concentration in the precursor solution increased. The average particle size was in the range 0.9-3.4 nm. The electrochemically active surface areas (ECSAs) of Pt were estimated using cyclic voltammetry. In contrast to the average particle size, the ECSAs increased as the NaPH2O2 concentration was increased. The decrease in the size of the Pt nanoparticles using NaPH 2O2 effectively increased the ECSA. This result indicated that the EBIRM combined with the use of NaPH2O2 to decrease the particle size is a useful and simple tool for the preparation of Pt nanoparticle catalysts with a high specific activity. © 2014 Springer Science+Business Media Dordrecht.


Ohkubo Y.,Osaka University | Kageyama S.,Osaka University | Seino S.,Osaka University | Nakagawa T.,Osaka University | And 4 more authors.
Journal of Nanoparticle Research | Year: 2013

Electrode catalysts composed of carbon-supported PtRu nanoparticles (PtRu/C) for use as a direct methanol fuel cell anode were synthesized by the reduction of precursor ions in an aqueous solution via irradiation with a high-energy electron beam. The effect of pH control in the precursor solution on the PtRu mixing state and the methanol oxidation activity was studied in order to enhance the catalytic activity for methanol oxidation. The PtRu/C structures were characterized by transmission electron microscopy, inductively coupled plasma atomic emission spectrometry, X-ray fluorescence spectrometry, and X-ray diffraction and X-ray absorption fine structure techniques. The methanol oxidation activity was evaluated by linear sweep voltammetry. The initial pH of the precursor solution has little influence on the average grain size for the metal particles (approximately 3.5 nm) on the carbon particle supports, but the dispersibility of the metal particles, PtRu mixing state, and methanol oxidation activity differed. The maintenance of a low pH in the precursor solution gave the best dispersibility of the PtRu nanoparticles supported on the surface of the carbon particles, whereas, a high pH gave the best PtRu mixing state and the highest oxidation current although a low dispersibility of the PtRu nanoparticles supported on the surface of the carbon particles was obtained. The PtRu mixing state strongly correlated with the methanol oxidation current. In addition, a high pH was more effective for PtRu mixing when using an electron beam irradiation reduction method, because the complexation reaction of the chelating agents was improved, which resulted in an enhancement of the catalytic activity for methanol oxidation. © 2013 Springer Science+Business Media Dordrecht.


Kageyama S.,Osaka University | Tamon N.,Osaka University | Kugai J.,Osaka University | Ohkubo Y.,Osaka University | And 4 more authors.
Materials Letters | Year: 2012

This paper describes a novel synthesis method of polymer-free PtCu/C nanoparticles using irradiation of a high-energy electron beam. The method is a simple and quick one-pot process in aqueous solution system. The compositions were analyzed by inductively coupled plasma-atomic emission spectroscopy. The microstructures of the samples were observed by using transmission electron microscope. PtCu nanoparticles with 2-nm size were deposited on carbon supports without any use of polymer stabilizers. X-ray diffraction analysis showed that the random alloy formations of PtCu were occurred without any heat treatment. Radiolytic synthesis was effectively applied to the synthesis of polymer-free PtCu/C. We pointed out a difference in alloying behaviors between PtCu and PtRu systems which was reported in a previous study. © 2012 Elsevier B.V. All rights reserved.

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