Effects of composition on structure and activity of PtRu/C catalysts

Abstract

A series of carbon supported PtRu bimetallic catalysts with varying Pt:Ru ratio were prepared and characterised using ex situ and in situXRD, in situ EXAFS at 0 V vs.RHE, ex situ XPS and monolayer CO stripping voltammetry. Although the catalysts were found to be well mixed/alloyed, with no evidence of unalloyed Ru (oxides) present, the surfaces of the electrocatalyst nanoparticles were found to be enriched with Pt compared to the nominal bulk composition. The methanol oxidation activities of the catalysts were determined in 1.0 mol dm⁻³ H₂SO₄. In agreement with published studies of polycrystalline bulk PtRu alloys the catalyst with a 0.6 surface fraction of Pt was found to give the best methanol oxidation activity at 30 °C. However, at 80 °C a greater surface fraction of Ru could be tolerated, with some activity at low current densities found for a Pt surface fraction as low as 0.2. The results support the conclusion that a limited amount of methanol dehydrogenation occurs at Ru sites or Ru dominated surface ensembles at 80 °C.