Fe and oxygen-vacancy engineering unlock coupled AEM-LOM pathways for active and durable alkaline OER

Fe-doping and oxygen vacancies synergistically optimize NiCo 2-x Fe x O 4-y for alkaline OER. • Oxygen vacancies facilitate OH − adsorption to accelerate the AEM pathway. • Fe species modulate oxygen covalency to trigger the LOM pathway. • Oxygen vacancies act as oxygen reservoirs to regenerate lattice oxygen. • Dynamic regeneration prevents structural collapse, harmonizing AEM and LOM. Developing oxygen evolution electrocatalysts that combine high activity, long-term durability, and low cost remains a central challenge because these properties are often constrained by competing reaction pathways. The adsorbate evolution mechanism (AEM) is limited by linear scaling relationships, whereas the lattice oxygen mechanism (LOM) offers higher activity but typically suffers from structural degradation due to lattice oxygen loss. Here, we demonstrate that Fe doping in NiCo 2 O 4 creates a synergistic interplay between Fe active sites and oxygen vacancies, enabling both enhanced activity and durability. Experimental and theoretical analyses reveal a dual-mechanism pathway: oxygen vacancies facilitate OH − adsorption to accelerate the AEM, while Fe species regulate O covalency to activate the LOM. Consequently, the optimized NiCo 1.4 Fe 0.6 O 4-y catalyst achieves an ultralow overpotential of 196 mV at 10 mA cm −2 . Furthermore, oxygen vacancies are proposed to facilitate lattice‑oxygen replenishment during LOM operation, thereby helping to mitigate structural degradation. This dynamic regeneration mechanism underpins the excellent long-term stability of more than 290 h. Overall, this work offers a practical strategy to break the activity–stability trade-off in oxygen evolution catalysis through oxygen-vacancy engineering of dual-mechanism pathways. Defect engineering synergistically unlocks coupled AEM and LOM pathways, with abundant oxygen vacancies accelerating intermediate adsorption and dynamically regenerating lattice oxygen, effectively breaking the intrinsic trade-off between catalyst activity and durability during alkaline water splitting. Download: Download high-res image (199KB) Download: Download full-size image