Atomic Structure of PtRu Nanoparticle Catalysts and Their Methanol Oxidation Activity
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1056-HH03-25
Atomic Structure of PtRu Nanoparticle Catalysts and Their Methanol Oxidation Activity Hiroaki Nitani1, Yusuke Honda1, Ryo Horioka1, Kosuke Ohara1, Takuya Kawaguchi1, Takashi Nakagawa2, Satoshi Seino1, Takao A. Yamamoto1, and Hideo Daimon3 1 Graduate School of Engineering, Osaka University, 2-1 Yamada-oka, Suita, Osaka, 565-0871, Japan 2 Graduate School of Science and Engineering, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo, 152-8552, Japan 3 Development & Technology Division, Hitachi Maxell Ltd., 6-20-1 Kinunodai, Tsukubamirai, Ibaraki, 300-2496, Japan ABSTRACT PtRu bimetallic nanoparticles supported on carbon nanoparticle (PtRu/C) catalysts were synthesized with radiation irradiation. The samples were analyzed by techniques of X-ray absorption fine structure (XAFS), transmission electron microscope (TEM) and X-ray diffraction (XRD). The results indicated that PtRu/C catalysts which were prepared by an electron beam irradiation had more homogeneous atomic arrangement than PtRu/C prepared by a gamma-ray irradiation. We found a clear correlation between the atomic structure and the catalytic activity of PtRu/C catalysts. These results supported the bi-functional mechanism. INTRODUCTION The direct methanol fuel cell (DMFC) uses liquid methanol as fuel, whereas other cell types use hydrogen gas. Because liquid methanol has higher energy density than hydrogen gas, it is easy to downsize the DMFC. So, the DMFC is one of most promising next generation’s mobile power sources such as cellular phones and mobile PCs and automobiles [1-3]. However, effective cell voltage of the DMFC is lower compared with the thermodynamic one because of significant overpotential caused by methanol oxidation occurring at anode surface. A key issue for commercialization of the DMFC is improvement of methanol oxidation activity in anode catalyst. The DMFC usually uses Pt catalysts for its anode catalyst, but Pt is essentially poisoned easily by CO which produced in methanol oxidation reaction. To resolve this problem, many scientists have been studying new Pt based alloys and found that PtRu alloy is the highest CO tolerance catalyst [4-6]. In our previous work, we synthesized PtRu alloy nanoparticles catalyst loaded on porous carbon support by using polyol process and we studied correlation between its structure and catalytic activity. The results showed that the atomic arrangement of Pt and Ru in the PtRu alloy nanoparticles is important factor for its catalytic activity [7, 8]. This result introduced some tuning of the catalyst structure for improvement of the methanol oxidation activity. However, it is difficult to control the atomic structure of PtRu nanoparticle catalyst by using polyol process, because Pt ion and Ru ion have different redox potentials. Therefore, we need new synthesis method which can control the structure of bimetallic nanoparticle. We adapt radiation irradiation process as the synthesis method [9]. In this process, the speed of the reduction of metallic ions depends on a dose rate of ir
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