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

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The oxygen evolution reaction (OER) is the primary kinetic bottleneck in water electrolysis, requiring catalysts that are both efficient and durable. Here, a MnCoNi–RuO 2 (MCN–RuO 2 ) 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 RuO 2 host lattice interfaced with MnO and spinel‐type CoNiO x 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 RuO 2 and IrO 2 . 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–RuO 2 as a versatile, Ir‐free platform and demonstrate multimetal doping with heterointerface engineering as a powerful strategy for designing next‐generation OER catalysts.