In Situ Reactivating Perovskite Oxide Catalysts in Alkaline Water Electrolyzers: A Generalized Approach Based on Selective Cation Leaching

Perovskite oxides have received great attention as promising electrocatalysts for the sluggish oxygen evolution reaction (OER), thanks to the highly active transition-metal oxyhydroxide surface formed under operando conditions. Such an in situ surface reconstruction is spontaneous under a potential bias, generating both the OER-active and the OER-inert domains simultaneously. We herein aimed at maximizing the activity of perovskite oxides via controlled surface evolution using two typical perovskites, i.e., Ba0.5Sr0.5Co0.8Fe0.2O3 (BSCF) and La0.6Sr0.4Co0.8Fe0.2O3 (LSCF), as the model catalysts. We first elucidated the active site evolution under high anodic potentials in 6 M KOH at 85 °C via combined microscopic, spectroscopic, and thermodynamic analyses. While the bulk integrity of both perovskites was maintained, a thin amorphous layer formed after biasing at 0.5 V overpotential. Being rich in transition-metal oxyhydroxide, this layer also contained significant amounts of Ba- and La-hydroxides. Guided by the Pourbaix diagram, we designed an in situ "re-activation" step by circulating a lightly acidified electrolyte in the electrolyzer to selectively remove inert A-site hydroxide deposits, resulting in substantially boosted OER activity and robustness. This work shows a facile and universal approach for reactivating perovskite oxide OER catalysts under industrially relevant conditions, opening opportunities for their application in real life.