Theoretical Insights into the Mechanism of Water Oxidation on Nonstoichiometric and Titanium-Doped Fe2O3(0001)

Fe2O3 is widely considered a promising material for converting solar energy through oxidizing water. We model the mechanism of water oxidation on Fe2O3(0001) surface in the presence of defects that have been recently modulated experimentally. We use a density functional theory type method (DFT + U) on several surface models that include oxygen vacancies iron vacancies, and Ti-Dopants. Our calculations reveal that these multiple defects do not change the cumulative free energy of the reaction, but do change the overpotential. Moreover, the mechanism details are different. The excess holes generated by iron vacancies suppress the first hydrogen cleavage reaction, the reduce the free energy for the final reaction step of oxygen release. This work sheds light into the origin of the thermodynamic limitations, paving the way toward possible control over surface reactivity.