Electrochemical Oxidation of Hydrolyzed Poly-Oxymethylene-Dimethylether by Pt and PtRu Catalysts on Ta-Doped SnO2 Supports for Direct Oxidation Fuel Cells

Abstract

We synthesized Pt and PtRu catalysts supported on Ta-doped SnO2 (Pt/Ta-SnO2, PtRu/Ta-SnO2) for the anodes of direct oxidation fuel cells fueled with poly-oxymethylene-dimethylether (POMMn, n = 3∼8). The onset potential for the oxidation of the hydrolyzed fuel of POMM3 (h-POMM3; methanol-formaldehyde mixtures with the composition equivalent to 100% hydrolyzed POMM3) on Pt/Ta-SnO2 and PtRu/Ta-SnO2 was at least 0.2 V lower than that on a commercial Pt2Ru3/carbon black (c-Pt2Ru3/CB). The Pt-based mass activities at 0.50 V (MA0.50V) of PtRu/Ta-SnO2 for the h-POMM3 and formaldehyde oxidations were more than four times larger than those of the c-Pt2Ru3/CB. Elemental tin was found to exist on the top surface, brought by the diffusion from the Ta-SnO2 support. The elemental tin may contribute to enhancing the anodic reaction via an acceleration of carbon monoxide oxidation by a bifunctional mechanism or ligand effect. Single cells using Pt/Ta-SnO2 and PtRu/Ta-SnO2 as anodes exhibited higher current densities in all voltage regions when supplied with the h-POMM3 fuels dissolved in water. We deduced that both the elemental tin diffusion from the Ta-SnO2 support to the catalyst nanoparticles and the unique fused-aggregate network structure of the Ta-SnO2 support contribute to enhancing the performance of POMMn-based fuel cells.