Defect-Rich FeNiCoO₄/MoO₃ Nanosheets as Efficient Electrocatalysts for the Oxygen Evolution Reaction

Exposing catalytically active sites and modulating the electronic structure of active metals are key strategies for enhancing oxygen evolution reaction (OER) performance. Leveraging the tunable interlayer anions in layered double hydroxides, we developed a scalable synthesis of high-performance OER catalysts consisting of FeNiCo spinel oxide and high-valence metal oxides (MoO₃, WO₃, CrO₃, V₂O₅). This approach integrates separate nucleation/aging steps, transition-metal oxyanion intercalation, and thermal oxidation. The resulting defect-rich ultrathin oxide nanosheets precisely regulate the electronic structure of active sites, shifting the rate-determining step (O* → OOH*) to improve the OER thermodynamics. These catalysts outperform commercial RuO₂ in both activity and stability. Remarkably, FeNiCoO₄/MoO₃ achieves a current density of 50 mA cm^-2 at an overpotential of just 238 mV with a Tafel slope of 41.12 mV dec^-1, exceeding all reported powder-based oxide OER catalysts. It also demonstrates an excellent 100 h stability at 50 mA cm^-2. This work provides a universal and scalable platform for designing efficient OER electrocatalysts.