Effect of Subsurface Vacancies on Oxygen Reduction Reaction Activity of Pt-Based Alloys

Density functional theory is used to evaluate geometric and electronic effects of the presence of vacancies in subsurface layers of Pt-based alloys composed by a monolayer of Pt on top of an alloy core for bimetallic Pt/PtM/Pt₃M (M = Co, Pd, Ir, Cu) and trimetallic Pt/M1₃M2 (M1, M2 = Pd, Cu; M1 ≠ M2) systems. Our model simulates metal porous structures arising after dealloying due to exposure of metal nanoparticles to oxidative conditions in acid medium. Enhanced oxygen reduction reaction activity experimentally observed in these structures is tested through the calculation of binding energies of O and OH. It is found that subsurface vacancies induce relatively weaker binding energies of O and especially of OH, and reduced Pt–Pt surface distances, which can explain the observed activity enhancement