Hydrated Proton Structure and Diffusion at Platinum Surfaces

Abstract

Water-mediated hydrated proton solvation and diffusion at two types of platinum–water interfaces—namely, the Pt(111) and the Pt(100) surfaces—is investigated using reactive molecular dynamics simulations. The adsorbed water molecules on these platinum surfaces create different hydrogen-bonding networks, resulting in different proton solvation and transport behavior. Free energy calculations show that the excess proton can be stably adsorbed on the Pt(111) surface, while on the Pt(100) surface it prefers to stay at the interface between the hydrophobic layer of adsorbed water and the bulk. The hydrated excess proton can be viewed as a charge defect in the adsorbed water layer, where it diffuses with a low rate due to the slow reorientational dynamics of the adsorbed water molecules. However, the proton can sample a larger surface area by hopping between the adsorbed layer and the bulk at the Pt(111) surface.