Understanding dissolution mechanism of oxide perovskites and activity tuning for O2 evolution by surface doping

Abstract

The oxygen evolution reaction (OER) is the major bottleneck in electrochemical water splitting. Development of efficient electrocatalysts from earth-abundant materials is essential. This study reports a design principle for tuning the catalytic efficiency and stability of perovskite oxides (ABO₃), focusing on SrMnO₃, SrFeO₃, SrCoO₃, and SrNiO₃ through B-site surface doping with Mn, Fe, Co, and Ni metal ions. Owing to multiple active sites and tunable oxidation states, these oxide surfaces exhibit a considerable reduction in thermodynamic overpotential (η_TD) upon doping. The dissolution free energy calculations are performed across a wide pH window (acidic to alkaline) and oxidative potentials to determine the Pourbaix stability and surface dissolution pathways. We find that SrCoO₃ and SrNiO₃ show the highest stability on doping with different transition metal atoms. Reaction free energy analysis indicates that the lattice oxygen mechanism generally outperforms the adsorbate evolution mechanism on the undoped surfaces. Surface doping results in a wide variation in the preferred reaction pathway. Mn-doped SrNiO₃ emerges as the most active system with η_TD of 0.34 V, while Fe doping enhances the activity of SrCoO₃ the most. Crystal orbital Hamilton population and electronic structure analyses show that modulation of the d-band center and surface structure deformation upon doping, influences the catalytic activity and stability. Using the activity descriptor G_max(η) at an applied η of 0.3 V, the corresponding rate-determining steps (RDS) are identified. While most sites follow a single-step RDS, Fe- and Co-doped SrNiO₃ exhibit multistep contributions. On varying the doping percentages of Fe on the SrCoO₃ surface, we find that 25% surface doping shows the highest catalytic activity for OER.