Structural analysis of sonochemically prepared PtRu versus Johnson Matthey PtRu in operating direct methanol fuel cells

Sonochemically prepared PtRu (3: 1) and Johnson Matthey PtRu (1: 1) were analyzed by X-ray absorption spectroscopy in operating liquid feed direct methanol fuel cells. The total metal loadings were 4 mg cm^-2 unsupported catalysts at the anode and cathode of the membrane electrode assembly. Ex situ XRD lattice parameter analysis indicates partial segregation of the Ru from the PtRu fcc alloy in both catalysts. A comparison of the in situ DMFC EXAFS to that of the as-received catalyst shows that catalyst restructuring during DMFC operation increases the total metal coordination numbers. A combined analysis of XRD determined grain sizes and lattice parameters, ex situ and in situ EXAFS analysis, and XRF of the as-received catalysts enables determination of the catalyst shell composition. The multi-spectrum analysis shows that the core size increases during DMFC operation by reduction of Pt oxides and incorporation of Pt into the core. This increases the mole fraction of Ru in the catalyst shell structure.