XANES STUDY OF UNDERPOTENTIAL DEPOSITED COPPER ON CARBON-SUPPORTED PLATINUM

Underpotential deposited (UPD) copper on carbon-supported platinum was investigated in-situ in 0.5 M H2SO4 at 0.05 V (SCE) by XANES (X-ray Absorption Near Edge Structure). By taking XANES spectra at the Cu K-edge and the Pt L(III)-edge it was possible to determine the valence state of the copper and observe modifications in the electronic structure of the platinum on adsorption of copper. The XANES for UPD copper shows that the adsorbed copper had an oxidation state close to Cu+. XANES features indicate strongly a tetrahedral coordination for the adsorbed Cu species. A reduction in intensity of the white line in the platinum XANES is consistent with a partial filling of empty Pt d-band vacancies on adsorption of copper. Thus, UPD species can modify the electronic structure of a platinum catalyst. The adsorbed Cu+ species are apparently associated with HSO4- ions.