Effects of atomic vibrations on the electronic structure and the photocatalytic efficiency of α-Fe2O3

For the photocatalytic water splitting, the oxygen evolution reaction on transition-metal oxide photoanodes is well known to be the bottleneck. As strongly correlated materials, strong electron-phonon couplings in transition-metal oxides indicate that atomic vibrations can greatly modify electronic structure and transport properties. By combining density functional theory and molecular dynamics, we study the effects of finite-temperature atomic vibrations on the band gaps, electronic localization, polaron formation, absorption spectra, and the band-edge levels in $\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{Fe}}₂{\mathrm{O}}₃$. Atomic vibrations are found to induce strong electronic localization near the band edges and facilitate the hole polaron formation, which can hinder the transport of the photogenerated holes. In addition, atomic vibrations push up the valence band edge, indicating an increased reaction barrier. This study identifies that atomic vibrations in transition-metal oxide photoanodes can limit the efficiency of the oxygen evolution reaction.