Fermi-Level-Dependent Defect Chemistry and Oxygen Evolution Reaction Activity of Fe-Doped and Oxygen-Deficient SrTiO3(001)

The oxygen evolution reaction (OER) on perovskite oxides is controlled by the interplay of dopant chemistry, defect charge states, and surface segregation, yet these factors are rarely treated on equal footing. Using first-principles density functional theory, we investigate how Fe dopants (FeTi) and oxygen vacancies (VO) in different charge states affect the OER on TiO2-terminated SrTiO3(001). We combine charge-dependent defect formation energies, segregation energies, and charge transition levels with OER free-energy profiles obtained in the computational hydrogen electrode framework. Neutral FeTi× preserves near-pristine activity, with overpotentials of 0.45–0.50 V compared to 0.46 V for the pristine surface, whereas the reduced states FeTi′ and FeTi″ raise the overpotential to as much as 1.37 V when intermediates bind to Ti sites adjacent to surface Fe. Oxygen vacancies segregate to the surface across the entire band gap (ΔEseg = −0.50 to −0.80 eV) but do not improve the activity:VO× and VO• overstabilize oxygenated intermediates (η up to 2.02 V), and only VO••retains a balanced pathway (η = 0.46 V in the bulk-like region). Because the stable charge state and the segregation tendency of each defect are set by the Fermi level, the OER overpotential itself becomes a Fermi-level-dependent quantity. These results establish Fermi-level-dependent defect chemistry as a framework for assessing defect-mediated OER activity, with potential applicability to other perovskite oxides containing multivalent dopants and native defects.