Probing adsorption phenomena on a single crystal Pt-alloy surface under oxygen reduction reaction conditions

The adsorption dynamics of *OH and *O species at Pt(111) and Cu/Pt(111) near-surface alloy (NSA) surfaces in oxygen-free and O2-saturated 0.1M HClO4 was investigated. Subsurface Cu modifies the electronic structure at the Pt(111) surface resulting in weaker bonding to adsorbates like *OH, *H or *O. This provides a basis for the high oxygen reduction activity of the NSA, as predicted by density functional theory calculations.

The shift in *OH adsorption of around 0.16V towards more positive potentials can be clearly monitored in absence of O2 and under the oxygen reduction reaction (ORR) conditions for the Cu/Pt(111) NSA. In both cases, for Pt(111) and NSA, the *OH(*O) adsorption dynamics is very similar in the absence of oxygen and under ORR conditions.

Therefore, theoretical assumptions about the coverage of adsorbates in the absence of oxygen can be reasonably extrapolated to the situation when oxygen reduction takes place at the surface. A ∼5-fold improvement in the ORR activity over the Pt(111) at 0.9V (RHE) was measured for the Cu/Pt(111) near-surface alloy.