Unleashing Electrocatalytic Oxygen Evolution Activity: Engineering Spin States in Strained Correlated Oxides for Enhanced Performance

Perovskite oxides have emerged as compelling contenders for catalyzing the oxygen evolution reaction (OER) due to their low cost, high efficiency, and structural flexibility. Nevertheless, unraveling the intricate structure-activity relationships within correlated oxides remains challenging, impeding the rational design of efficient catalysts. Here, using LaCoO₃ epitaxial thin films as a model system, we illustrate a direct correlation between the spin state and OER activity. Through comprehensive investigations via X-ray absorption spectroscopy, scanning transmission electron microscopy, and first-principles calculations, we pinpoint that the enhanced OER activity observed in the tensile-strained films originates from lattice oxygen oxidation triggered by strain-engineered high-spin Co³⁺. Particularly, the high-spin sites correlated oxygen vacancies during OER lead the reaction into a new pathway, facilitating both the deprotonation of OH* at the metal site and the formation of O-O bonds at the oxygen redox center. Our findings reveal the intricate interplay among strain, spin-state transition, and the transformation of OER mechanism, providing valuable insights for correlated oxide electrocatalysts.