Phase Engineering of Cobalt‐Based Perovskite Oxides Toward Enhanced Oxygen Evolution Electrocatalysis

Electrochemical water splitting provides a sustainable route for hydrogen production, yet its efficiency is largely constrained by the intrinsically sluggish kinetics of the oxygen evolution reaction (OER) at the anode. Cobalt‐based perovskite oxides are promising OER electrocatalysts in alkaline solutions, but their performance strongly depends on crystal structure and electronic configuration. Herein, a phase engineering strategy based on thermal reduction in inert atmospheres, which transforms a hexagonal‐structured perovskite with poor OER activity into a cubic‐structured perovskite with markedly enhanced OER kinetics, is demonstrated. This cubic phase exhibits a reduced Co valence and increased oxygen vacancy concentration, leading to a 20‐fold increase in intrinsic OER activity compared to the hexagonal precursor. Its performance also surpasses that of state‐of‐the‐art perovskites and noble metal‐ and non‐noble metal‐based benchmarks. This work highlights phase transformation as a powerful approach to optimize perovskite oxides for efficient OER electrocatalysis.