Vacancy-Associated La-Ir Pairs Enable Water-Derived Oxygen-Hydroxyl Coupling for Durable Low-Ir PEM Water...

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.