Relay Low‐Valence Co Dynamic Cycle Stabilized CoFe Oxyhydroxides for 700 h at 1 A cm −2 in Alkaline Water Oxidation

ABSTRACT Although the iron dissolution rate is significantly lower in bimetallic CoFeO x H y than monometallic FeOOH, the facile formation of Co 4+ can still activate the lattice oxygen mechanism (LOM) with intense dynamic oxygen migration, leading to iron dissolution. Herein, we design a self‐driven Co 2+ /Co 3+ ‐dominated low‐valence cycle by introducing metallic Co into CoFeO x H y , which facilitates the adsorbate evolution mechanism (AEM), not LOM. Moreover, the electron compensation effect induced by oxygen vacancy (O V ) in CoFeO x H y has been utilized to transfer electrons to Co 3+ , promoting the Co 3+ → Co 2+ transition. Therefore, the “relay” effect based on metallic Co and O V initiates and maintains a dynamic Co 2+ /Co 3+ low‐valence cycle, minimizing Co 3+ →Co 4+ conversion, thereby strengthening AEM and reducing iron dissolution. XAFS characterizations confirm that the solid‐phase reaction between NaBH 4 and Co(OH)F yielded metallic Co and O V . The as‐prepared L‐Co(OH)F‐FeOOH demonstrates long‐term stability of 730 h at 1 A cm −2 . Furthermore, it maintains stable performance for 200 h at 0.5 A cm −2 in an anion exchange membrane water electrolyzer (AEMWE). Theoretical and experimental studies confirm that the formation of a dynamic low‐valence Co 2+ /Co 3+ cycle realizes the shift of catalytic mechanism from LOM to AEM, which stabilizes the Fe─O bond and thus enhances the stability of L‐Co(OH)F‐FeOOH.