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

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 Cu²⁺ 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 WO₃ 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/WO₃ interface strengthens nitrate capture and lowers the barriers of key hydrogenation steps. The resulting system delivers NH₃ Faradaic efficiencies above 90% over a broad potential window in strong acid and sustains ampere-level operation for over 1000 h in a 25 cm² membrane electrode assembly with NH₃ production rates up to 0.37 g h^-1.