Potential-Dependent Reversible Restructuring of Pt-Au Alloy Electrocatalysts

The distribution of metals in alloy nanoparticles is a key parameter in their electrochemical performance. Here, we show that for Pt-Au alloys this distribution dynamically responds to the electrochemical environment. Using electrochemical X-ray photoelectron spectroscopy, we find that the surface composition of the alloy can range from stoichiometric to Pt-enriched, depending on the applied potential. The driving factors for this restructuring are the differences in electronegativity and mobility between Pt and Au. At potentials below 1.5 V_RHE, the slightly more reactive (less electronegative) Pt shows surface enrichment, which slowly increases as the potential is raised and increasingly oxidizing adsorbates are formed. Above 1.5 V_RHE, oxidation of the more mobile Au atoms becomes possible, which is kinetically favored over Pt oxidation, thereby driving Au toward the surface. All surface dynamics are found to be highly reversible, even at room temperature. This facile rearrangement suggests that dynamic restructuring of alloy nanoparticles occurs in a wide range of conditions, and should therefore be taken into account in alloy electrocatalyst design.