Bond Competition in Iron Dissolution from Spinel Oxides during Water Oxidation

Irreversible dissolution of redox-active transition metals during the oxygen evolution reaction remains a major challenge in developing durable water electrolysis catalysts, particularly for Fe-containing spinel oxides. Despite strategies to mitigate Fe dissolution, its atomistic pathway and mechanism remain unclear. Here, we combine static and dynamic ab initio modeling with electrochemical tests to investigate Fe dissolution in NiFe₂O₄ and CoFe₂O₄ spinels. Instead of viewing Fe instability as an intrinsic property, we show that it arises from bond strength competition within the M-O-Fe (M = Ni or Co) linkages. A stronger M-O bond (as in Co-O) weakens the adjacent Fe-O bond under electrochemical bias, making Fe dissolution more favorable in CoFe₂O₄ than that in NiFe₂O₄. Such asymmetric bond competition leads to enhanced Fe dissolution while simultaneously facilitating surface reconstruction and catalyst deterioration. This work establishes bond competition as a decisive descriptor for metal dissolution, offering practical guidelines for designing stable OER catalysts.