OH Binding Energy as a Universal Descriptor of the Potential of Zero Charge on Transition Metal Surfaces
Sara R. Kelly, Hendrik H. Heenen, Nitish Govindarajan, Karen Chan, Jens K. Nørskov
Abstract
The potential of zero charge (UPZC) is an important quantity of metal–water interfaces that are central in many electrochemical applications. In this work, we use ab initio molecular dynamics (AIMD) simulations to study a large number of (111), (100), (0001), and (211) and overlayers of transition metal–water interfaces to identify simple descriptors to predict their UPZC. We find a good correlation between water coverage and the work function reduction Δϕ which is defined by the difference of the work function in a vacuum and in the presence of water. Furthermore, we determine the vacuum binding energies of H2O and *OH species as good descriptors for the prediction of water coverage and thereby of Δϕ. Our insights unify different facet geometries and mixed metal surfaces and thereby generalize recent observations. We further present a scheme to predict UPZC based only on the *OH binding and the vacuum work function estimated from static DFT calculations. This formalism is applicable to all investigated metals and mixed metal surfaces including terrace and step geometries and does not require expensive AIMD simulations. To evaluate physical influences to UPZC, we decompose Δϕ into its orientational (Δϕorient) and electronic (Δϕel) component. We find Δϕorient to be a facet-dependent property and a major contributor to Δϕ on (211) surfaces, while Δϕel strongly depends on the metal identity.