Multimetal Doping and Heterostructure Engineering of RuO ₂ for Durable and Efficient Oxygen Evolution

The oxygen evolution reaction (OER) is the primary kinetic bottleneck in water electrolysis, requiring catalysts that are both efficient and durable. Here, a MnCoNi-RuO₂ (MCN-RuO₂) heterostructured catalyst synthesized via a controlled impregnation-annealing-etching process that integrates multimetal doping with mixed-phase oxide formation is reported. Structural analyses reveal a RuO₂ host lattice interfaced with MnO and spinel-type CoNiO _<i>x</i> domains, generating lattice distortion, oxygen vacancies, and defect-rich interfaces that tune the electronic structure and enrich active sites. Electrochemical tests demonstrate overpotentials as low as 200 mV at 10 mA cm^-2, a low Tafel slope, and markedly improved stability relative to commercial RuO₂ and IrO₂. The catalyst also retains high activity under acidic conditions and, when implemented in an anion exchange membrane water electrolyzer, sustains industrially relevant operation for 100 h with minimal degradation. Density functional theory calculations reveal that multimetal incorporation drives charge redistribution, lowers the work function, and shifts Ru-4d states, reducing the barrier for the rate-determining *O → *OOH step while enhancing stability against Ru dissolution. These findings establish MCN-RuO₂ as a versatile, Ir-free platform and demonstrate multimetal doping with heterointerface engineering as a powerful strategy for designing next-generation OER catalysts.