Orientation Sensitivity of Oxygen Evolution Reaction on Hematite

The sensitivity of the surface orientation on photoelectrochemical water oxidation has recently been reported by experimental studies. However, a detailed theoretical understanding is still missing. Density functional theory + Hubbard U (DFT + U) calculations are therefore carried out in order to investigate the oxygen evolution reaction (OER) on hematite (Fe2O3) surfaces for five surface orientations, namely (100), (210), (101), (021), and (211). The free energies of four proton-coupled electron transfer steps and the OER overpotential were calculated, and the trend in activity was analyzed. For the (100) orientation, two adsorbate-adsorbate distances were studied. Interestingly, a very low overpotential of 0.52 V was found for the (100) surface with a bridge site (adsorbate on a bridge of two Fe atoms) configuration that benefited from adsorbate-adsorbate interactions.