Vacancy‐Associated La–Ir Pairs Enable Water‐Derived Oxygen‐Hydroxyl Coupling for Durable Low‐Ir PEM Water Electrolysis

ABSTRACT Developing highly stable, low‐iridium catalysts is critical for acidic oxygen evolution, but is limited by structural degradation driven by acid corrosion and voltage polarization. Herein, we report an iridium and lanthanum co‐doped manganese‐cobalt spinel catalyst, Ir,La‐MCO δ , featuring octahedral La–Ir pairs (La oct –Ir oct ) with a theoretical favorable configuration of adjacent bridging and Ir z ‐axis oxygen vacancies. This low‐Ir catalyst Ir,La‐MCO δ (0.12 mg Ir cm −2 ) exhibits an overpotential of merely 220 mV at 10 mA cm −2 in pH = 1 electrolyte, and demonstrates robust operation for over 1550 h at 1 A cm −2 in a proton exchange membrane (PEM) water electrolyzer. Coupled (quasi)in situ characterizations and operando spectroscopy reveal that the adjacent oxygen vacancies mediate the evolution of oxygen intermediates, enabling water‐derived oxygen‐hydroxyl coupling with negligible lattice oxygen involvement, via a decoupled proton–electron transfer pathway. This mechanism preserves the structural integrity of the catalyst and yields a calculated reaction free‐energy change of merely 0.38 eV ( U = 1.23 V) for the most unfavorable oxygen‐hydroxyl coupling elementary step, thereby endowing Ir,La‐MCO δ with exceptional durability. This work provides a valuable mechanistic insight into designing highly stable defective catalysts.