Unveiling pH-Dependent Mechanistic Shifts in Cu2O-Catalyzed Nitrate Electroreduction for Selective Ammonia Synthesis

The electrocatalytic nitrate reduction reaction (NO 3 RR) offers a sustainable route for ammonia synthesis, yet its practical implementation requires catalysts adaptable to pH fluctuations inherent in industrial wastewater systems. Herein, Cu 2 O nanocubes as a model catalyst is synthesized and decoupled the pH-dependent reaction mechanisms with systematic experimental investigations. In acid electrolytes, the catalyst exhibited 93.3% faradaic efficiency for NH 3 with a yield rate of 34.6 mg h −1 mg cat −1 at −0.7 V versus. RHE. In contrast, in alkaline and neutral electrolytes, NH 3 synthesis is impeded by the formation of NO 2 - which served as the predominant by-product. Through operando infrared spectroscopy analysis, proton availability as the pivotal regulator is identified: Acidic media facilitates the further conversion of * NO 2 intermediates into NH 3 via the NOH pathway, whereas H + -deficient environments in neutral/alkaline conditions divert reaction flux through the NHO pathway. This mechanistic elucidation establishes proton concentration as a key parameter for steering nitrate-to-ammonia conversion efficiency.