Fast Preparation of PtRu Catalysts Supported on Carbon Nanofibers by the Microwave-Polyol Method and Their Application to Fuel Cells
Masaharu Tsuji,*,§,# Masatoshi Kubokawa,# Ryuto Yano,# Nobuhiro Miyamae,# Takeshi Tsuji,§,# Mun-Suk Jun,#,† Seonghwa Hong,† Seongyop Lim,† Seong-Ho Yoon,§,# and Isao Mochida†
Institute for Materials Chemistry and Engineering, KyushuUniVersity, Kasuga 816-8580, Japan, Graduate School of Engineering Sciences, Kyushu UniVersity, Kasuga 816-8580, Japan, and Art, Science and Technology Center for CooperatiVe Research, Kyushu UniVersity, Kasuga 816-8580, Japan ReceiVed July 28, 2006. In Final Form: NoVember 18, 2006
PtRu alloy nanoparticles (24 ( 1 wt %, Ru/Pt atomic ratios ) 0.91-0.97) supported on carbon nanofibers (CNFs) wereprepared within a few minutes by using a microwave-polyol method. Three types of CNFs with very different surface structures, such as platelet, herringbone, and tubular ones, were used as new carbon supports. The dependence of particles sizes and electrochemical properties on the structures of CNFs was examined. It was found that the methanol fuel cell activities of PtRu/CNF catalysts were in theorder of platelet > tubular > herringbone. The methanol fuel cell activities of PtRu/CNFs measured at 60 °C were 1.7-3.0 times higher than that of a standard PtRu (29 wt %, Ru/Pt atomic ratio ) 0.92) catalyst loaded on carbon black (Vulcan XC72R) support. The best electrocatalytic activity was obtained for the platelet CNF, which is characterized by its edge surface and high graphitization degree.Introduction
Carbon-supported PtRu alloy nanoparticles have been most widely applied in fuel cell due to their high electrocatalytic activity accompanied by high protection ability for carbon monoxide poisoning. Their electrocatalytic activity strongly depends on the particle size and distribution, carbon supports, and dispersion of catalysts on the supports. It has been reported that PtRuparticles about 3.0 nm in diameter displayed the highest catalytic activity for methanol electrooxidation.1 It is still a challenge to prepare the PtRu particles with a suitable and uniform size on carbon supports for preparing high-performance catalysts for fuel cells. If high electrochemical activity can be obtained at low PtRu concentrations, we can save expensive rare metals such as Pt and Ru. WhenPt and PtRu particles loaded on carbon supports are prepared by using such conventional methods as impregnation and pre-precipitation methods, it usually takes 1 day at least to carefully reduce and precipitate these particles under controlled environments.2,3 In recent years, a microwave (MW)-assisted heating method has received great attention as a promising method for the preparation ofmonodispersed Pt and PtRu catalysts on carbon supports. The MW-assisted method is superior in terms of its simplicity and rapidity, compared to the above conventional methods. Until now, Pt and PtRu catalysts supported on carbon black (e.g., Vulcan XC72) and carbon nanotubes have been
* To whom correspondence should be addressed. E-mail: tsuji@ cm.kyushu-u.ac.jp. § Institute for Materials Chemistry andEngineering. # Graduate School of Engineering Sciences. † Art, Science and Technology Center for Cooperative Research.
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prepared by using an MW-assisted heating method, and their electrochemical properties have been measured.4-7 Physicochemical properties of catalyst...