Role of surface termination and strain for oxygen incorporation on Fe-doped SrTiO₃ surfaces

Strain engineering is a promising approach to control the oxygen reduction reaction (ORR) kinetics of perovskite cathodes in solid oxide fuel cells (SOFCs). For multi-component oxide materials such as perovskite, there are two main strain effects: altering the surface reactivity and modifying the surface chemical composition. Our previous study (Energy Environ. Sci. 11 (2018) 71–77) showed that applying tensile strain enhances the oxygen exchange kinetics on SrTiFeO_3−δ (STF) surfaces by suppressing Sr segregation. However, the potential impact of changes in surface reactivity by strain on the oxygen exchange kinetics of STF remains unexplored yet. To address this gap, density functional theory (DFT) calculations are performed to evaluate the strain effect on oxygen incorporation on SrO and (Ti,Fe)O₂ (001) terminations of STF surfaces. The presence of surface vacancies is necessary for O₂ activation and dissociation. With the assistance of oxygen vacancies, O₂ incorporation is favorable on the (Ti,Fe)O₂ surface over the SrO surface. Tensile strain facilitates O₂ incorporation kinetics on the (Ti,Fe)O₂ surface, but its effect is weak on the SrO surface. Our results demonstrate that the enhanced oxygen surface exchange kinetics due to tensile strain in STF result not only from the inhibition of Sr segregation but also from an increase in O₂ incorporation.