Defect‐Rich Ir Single‐Atom/NiMnO _x Catalyst: From Surface Reconstruction to Practical PEM Electrolysis

ABSTRACT

Developing highly active and durable catalysts for the acidic oxygen evolution reaction (OER) remains a key challenge for proton exchange membrane water electrolysis (PEMWE). Herein, we report an efficient OER catalyst constructed via a low‐temperature calcination‐hydrothermal ion‐exchange method. A defect‐rich amorphous NiMnO _x support, derived from spinel NiMnO ₃ , is employed due to its abundant surface dangling bonds and oxygen vacancies, which enable effective anchoring of Ir single atoms and activation of lattice oxygen. The engineered amorphous structure with abundant surface defects, together with strengthened Ir─O coordination, stabilizes isolated Ir sites and promotes charge transfer. Density functional theory calculations reveal that efficient electron transfer channels were established between Ir and NiMnO _x , enabling precise regulation of d‐band centers through p–d orbital coupling, optimizing oxygen intermediate binding energies. As a result, the Ir _SA ‐NiMnO _x catalyst exhibits exceptional performance in acidic OER, requiring only 193 mV overpotential at 10 mA cm ⁻² , outperforming commercial IrO ₂ (290 mV), and demonstrating outstanding stability for 800 h at 200 mA cm ⁻² . More importantly, the Ir _SA ‐NiMnO _x exhibits a potential‐dependent OER mechanism (oxide pathway mechanism, OPM, at low potentials and synergistic oxide pathway mechanism‐lattice oxygen mechanism, OPM‐LOM, at higher potentials) and delivers improved performance in practical PEMWE systems (1 A cm ⁻² @1.85 V) with the advantage of spray‐coating fabrication. This work provides a strategy for designing efficient OER catalysts and offers insights into the relationship between surface reconstruction and single‐atom catalysis.