Surface Characterization of Ordered Intermetallic Compounds PtBi and PtPb

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D.R. Blasini^ab, D. Rochefort,^a, D.M. Smilgies^b, E. Fachini^c, D.r. Cabrera^c, and H.D. Abruña^a
aChemistry and Chemical Biology Department, Baker Laboratory, Cornell University, Ithaca NY 14853
^bCornell High Energy Synchrotron Source (CHESS), Wilson Laboratory, Cornell University, Ithaca, NY 14853
^cChemistry Department, University of Puerto Rico, Río Piedras Campus, San Juan 00931-3346, Puerto Rico

Abstract:
The surface composition and structure of bulk electrodes made from the ordered intermetallic compounds PtBi and PtPb was studied by ex-situ X-ray photoelectron spectroscopy (XPS) and grazing incidence diffraction (GID) after being subjected to various electrochemical treatments.  Analysis of the freshly polished surfaces shoed that the less-noble metals Bi and Pb are oxidized to significant extent.  Upon cycling to increasingly positive potentials, the proportion of oxidized Bi and Pb decreases gradually to reach the minimal values at +400 mV vs. Ag/AgCl.  The diminution observed are due to leaching of surface oxides Bi₂O₃ on PtBi and PbCO₃ or Pb(OH)₂ on PtPb, rather than to oxide reduction to the elemental state.  When the potential sweep is set up to higher values, we noticed a linear decrease in the less-noble metal surface concentration, along with a slight increase in the amount of the species in their oxidized state (Bi₂O₃ for PtBi and PbSO₄ for PtPb).  The results obtained here corroborate with our previous observations on the electrochemical pre-treatment effects on these intermetallic phases for electrocatalytic oxidation of formic acid.