Electrolyte‐Regulated Self‐Healing Cu/Oxide Interfaces for Stable Electrocatalysis in Strong Acid

ABSTRACT Metastable metal active sites are inherently difficult to preserve under strongly corrosive electrochemical conditions, because continuous dissolution depletes the catalytically relevant surface population during operation. Here, we show that soluble metal ions can be used as an external chemical reservoir to sustain a dynamic catalytically active state through an electrolyte‐regulated dissolution–redeposition equilibrium. Using acidic nitrate‐to‐ammonia electrosynthesis as a model system, we demonstrate that dissolved Cu 2+ continuously replenishes Cu active sites, thereby mitigating catalyst degradation by maintaining a dynamic steady‐state active‐site population rather than relying on a static catalyst structure. Coupling this concept with acid‐stable WO 3 nanorods organizes the dynamic Cu reservoir into a hierarchically dispersed interfacial active state composed of anchored single atoms and replenishable nanoclusters, stabilized by strong Cu─O─W coupling. Operando spectroscopy, x‐ray absorption analysis, and theory reveal that this adaptive Cu/WO 3 interface strengthens nitrate capture and lowers the barriers of key hydrogenation steps. The resulting system delivers NH 3 Faradaic efficiencies above 90% over a broad potential window in strong acid and sustains ampere‐level operation for over 1000 h in a 25 cm 2 membrane electrode assembly with NH 3 production rates up to 0.37 g h −1 .