Sol-gel derived WOx and WOx/Pt films for direct methanol fuel cell catalyst applications

WOx was synthesised from W(OC2H5)(6) by two different methods using the sol-gel (SG) approach, Type 1 using ethanol as the solvent, while Type 2 was water-based. Films and powders made from these sols were subjected to analysis by cyclic voltammetry (CV), powder X-ray diffraction (XRD), and scanning electron microscopy (SEM). Sweep rate experiments revealed that compared to Type I films, Type 2 films have a significantly greater number of electroactive WOx sites, and that a smaller proportion of the total active sites are surface sites, indicative of a higher film porosity (consistent with the SEM results). XRD analysis showed that both Type 1 and Type 2 WOx were poorly crystallised. However, the patterns for the two WOx types were distinctly different, with Type 2 WOx giving a more well-defined pattern. WOx sols were also successfully combined with a pre-formed Pt sol. Unlike Pt-only catalysts, methanol oxidation currents on Type 2 WOx/Pt films did not decay rapidly with potential cycling, indicating the occurrence of co-catalytic behaviour, while Type I films were not very active, overall. The low resistance exhibited by the WOx component makes it suitable as an ionically and electronically conducting support for direct methanol fuel cell electrocatalysts. (C) 2005 Elsevier Ltd. All rights reserved.