Characterization of Hole States at the Zn-Doped Hematite/Water Interface from Ab Initio Simulations

Abstract

Hole states at the surface of hematite (α-Fe2O3) are highly influential in the material’s performance as a photoanode for the oxygen evolution reaction. Zn-doping of hematite is known to both lower the overpotential for oxygen evolution and introduce hole carriers near the surface. In this work, hole states at the aqueous interface of hematite (0001) were characterized using density functional theory-based ab initio molecular dynamics (AIMD) together with hybrid density functional theory (DFT) calculations of the electronic structure. PBE0 with 12% exact exchange calculations of Zn-doped hematite (0001) slabs in vacuum revealed a hole state within the band gap of hematite, which was spatially localized on a Fe-O moiety in an adjacent layer of the slab. AIMD of the (0001) slab in contact with water was propagated at the PBE+D3 and PBE+U+D3 levels of theory, with hybrid PBE0 calculations performed on snapshots every 200 fs. Under both protocols we observed the fluctuation of the hole state energy within the band gap and the localization of the hole at the aqueous interface. Zn doping had an overall marginal effect on the interfacial hydration structure and hydrogen bonding dynamics. These calculations showed that Zn doping introduces surface-local hole states in the band gap at energies close to the O2/H2O redox level, providing atomistic insights into the lower overpotential observed for Zn-doped hematite and more broadly the potential role of surface-local hole states in driving water oxidation.