Hybrid Functional Study of the Electro-oxidation of Water on Pristine and Defective Hematite (0001)

In this study, water oxidation on both pristine and hematite containing oxygen vacancies was investigated using hybrid functional methods. The onset potentials for R–Fe–Fe–(OH)₃ and R–Fe–Fe–O₃ surface terminations were determined. It is found that oxygen vacancy stabilizes O adsorption on both terminations. The electronic structure was studied in order to explain the obtained reaction energy landscape. The density of states (DOS), projected density of states (PDOS), and the projected Crystal Orbital Hamilton Population (pCOHP) of the bond between the O and surface Fe atom of both terminations were plotted in order to explain the stabilization caused by oxygen vacancy. The pCOHP plot clearly illustrates a change in bond strength and provides a direct explanation for the stabilization. The results show that the presence of subsurface oxygen vacancies increase the overpotential for electro-oxidation of water and that the lowest overpotential is found on oxygen-terminated hematite.