Ethanol oxidation on novel, carbon supported Pt alloy catalysts - Model studies under defined diffusion conditions

The structure, surface composition and activity/selectivity for ethanol oxidation of carbon supported Pt alloy catalysts with different composition and catalyst loading, which were synthesized via the polyol-route, were investigated and characterized by microscopic/spectroscopic methods (TEM, EDX, XRD) and electrochemical (RDE, on-line DEMS) measurements under well-defined transport and diffusion conditions. The performance of the polyol-type Pt/C (20 wt.%), PtRu/C (20, 40 and 60 wt.%), and Pt3Sn/C (20 wt.%) catalysts was compared with that of commercial Pt/C, PtRu/C and Pt3Sn/C (E-Tek) catalysts. The metal particle sizes of the polyol-type catalysts are significantly smaller than those of the corresponding commercial catalysts, nevertheless both the mass specific activities and, more pronounced, the inherent, active surface area specific activities are lower than those of the commercial catalysts, which is related to the lower degree of alloy formation in the polyol-type catalysts. For all catalysts, incomplete ethanol oxidation to C2 products (acetaldehyde and acetic acid) prevails under conditions of this study, CO2 formation contributes by <= 1% for potentiostatic reaction conditions. The lower activity of the polyol-type catalysts is mainly due to the lower activity for acetaldehyde formation. Implications and further strategies for fuel cell applications are discussed. (c) 2006 Elsevier Ltd. All rights reserved.