Sol–gel derived WO x and WO x/Pt films for direct methanol fuel cell catalyst applications

Abstract

WO x was synthesised from W(OC 2H 5) 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 1 films, Type 2 films have a significantly greater number of electroactive WO x 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 WO x were poorly crystallised. However, the patterns for the two WO x types were distinctly different, with Type 2 WO x giving a more well-defined pattern. WO x sols were also successfully combined with a pre-formed Pt sol. Unlike Pt-only catalysts, methanol oxidation currents on Type 2 WO x /Pt films did not decay rapidly with potential cycling, indicating the occurrence of co-catalytic behaviour, while Type 1 films were not very active, overall. The low resistance exhibited by the WO x component makes it suitable as an ionically and electronically conducting support for direct methanol fuel cell electrocatalysts.