Architecture of Bimetallic PtxCo1-x Electrocatalysts for Oxygen Reduction Reaction As Investigated by X-ray Absorption Spectroscopy

Carbon-supported PtxCo1-x alloy nanoparticles are prepared via a modified Watanabe's process for oxygen reduction reaction (ORR). The relationship between the variations in alloying extent and Pt d-band vacancies in Pt-Co/C catalysts, which are tunable by changing the Pt and Co composition, are systematically studied. All of the catalysts are characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), cyclic voltammetry (CV), and XAS. TEM images indicate that the dispersion of the metal nanoparticles on the carbon support is uniform. The XAS technique containing both X-ray absorption near edge spectroscopy (XANES) and extended X-ray absorption fine spectroscopy (EXAFS) is utilized to extract the Pt d-band vacancies and alloying extent of Pt and Co in PtxCo1-x nanoparticles, respectively. Rotating disk electrode measurements of PtxCo1-x nanoparticle catalysts with various Pt:Co atomic cornpositions (3:1, 1:1, and 1:3) reveal that Pt1Co1/C nanocatalyst showed enhanced ORR activity. It is proposed that ORR activity enhancement of Pt1Co1/C nanocatalyst is attributed to the higher alloying extent of platinum and cobalt as well as the promising electronic structure offered by the lower unfilled Pt d-states when compared to the pure Pt.