Electrochemical Properties of Carbon-Supported Metal Nanoparticles Prepared by Electroplating Methods

Abstract

There is a great demand for more potent, lightweight, efficient and reliable power-sources for a variety of transportation, portable electronics and other applications (Lamm et al., 2003). Batteries and fuel cells are alternative energy devices but batteries are only viewed as a short/mid-term option (Kuk & Wieckowski, 2005). Since transportation represents a significant portion of world energy consumption and contributes considerably to atmospheric pollution, the development of an appropriate fuel cell system is an important issue from both economical and environmental points of view (Arico et al., 2001). Direct methanol fuel cells (DMFCs) are an attractive portable power source owing to their high energy density, easy fuel handling, and a low operating temperature (Arico at al., 2000; Chen & Tang, 2002; Ren et al., 2000; Witham at al., 2003). However, DMFCs entail some serious technical obstacles. One is the relatively slow kinetics of the methanol oxidation reaction at an anode (Lima at al., 2001). Methanol oxidation reaction involves the transfer of six electrons to the electrode for complete oxidation to carbon dioxide. From a general point of view, almost all electro-oxidation reactions involving low molecular weight organic molecules, such as CO, CH3OH, C2H5OH, HCOOH, HCHO, require the presence of a Ptbased catalyst (Arico at al., 2001). Platinum (Pt) has a high activity for methanol oxidation (Katsuaki at al., 1988, 1990; Watanabe at al., 1989). Pt is involved in two key steps occurring during the methanol oxidation route. One is the dehydrogenation step and the second is the chemisorption of CO (Arico at al., 2001). Pt electrocatalyst will be poisoned by intermediates of methanol oxidation, such as CO. To solve this problem, Pt was alloyed with other transition metals. Since the mid-1970s, to promote methanol electro-oxidation by Pt, the catalyst surface has been modified by the addition of a second metal to Pt (Gotz & Wedt, 1998; Hamnett at al., 1988; Mukerjee at al., 1999). The resulting Pt–Ru binary metallic catalyst is commonly accepted as the best electrocatalyst for methanol oxidation (Chu & Jiang, 2002; Gasteiger at al., 1993; Ticianelli at al., 1989; Ueda at al., 2006). In commercializing fuel cells, one of the most critical problems is the cost of metal catalysts deposited on electrodes (Chen at al., 2005; Frelink at al., 1995; Guo at al., 2005; Xiong & Manthiram, 2005; Kim at al., 2005; Kuk & Wieckowski, 2005; Qiao at al., 2005). Generally, platinum (Pt) or platinum alloy-based nanoclusters, which are impregnated on carbon supports, are the best