Methanol Oxidation at Porous Co-Electrodeposited Pt-Ir Thin Films

Pt-Ir films, formed by the mixing of Pt and Ir sols together, were shown earlier to be catalytic towards the methanol oxidation reaction (MOR), although neither the composition nor the microstructure of these films were reproducible. In the present work, thin and porous Pt-Ir films, with controlled compositions, were electrodeposited on Au at a charge efficiency of close to 100% (as shown by in situ mass measurements). X-ray photoelectron spectroscopy demonstrated that the Pt-Ir film composition is homogeneous in all dimensions and closely matches that of the deposition solution, although the outer surface of these films is shown to be enriched in Pt. These thin Pt-Ir films, with their highly controlled compositions, were then studied for their MOR activity (of relevance to direct methanol fuel cells), calculated on a total metal basis, revealing that the optimum surface Pt:Ir atomic ratio is roughly 3:1.