PNNL

Abstract

Metal oxide growth, dissolution, and redox reactivity depend on the structure and dynamics at the interface with aqueous solution. We present the most definitive analysis to date of the hydrated naturally abundant r-cut (11 ¯02) termination of the iron oxide hematite (-Fe2O3). In situ synchrotron X-ray scattering analysis reveals a ridged lateral arrangement of adsorbed water molecules hydrogen bonded to terminal aquo groups. Large-scale hybrid-functional density functional theory-based molecular dynamics (DFT-MD) simulations show how this structure is dynamically stabilized by picosecond exchange between aquo groups and adsorbed water, even under nominally dry conditions. Surface pKa prediction based on bond valence analysis suggests that water exchange may influence the proton transfer reactions associated with acid/base reactivity at the interface. Our findings rectify inconsistencies between existing models and may be extended to resolving more complex electrochemical phenomena at metal oxide-water interfaces.