Tandem Active Sites in Cu/Mo‐WO3 Electrocatalysts for Efficient Electrocatalytic Nitrate Reduction to Ammonia

Electrocatalytic NO3− reduction to NH3 is a promising technique for both ammonia synthesis and nitrate wastewater treatment. However, this conversion involves tandem processes of H2O dissociation and NO3− hydrogenation, leading to inferior NH3 Faraday efficiency (FE) and yield rate. Herein, a tandem catalyst by anchoring atomically dispersed Cu species on Mo‐doped WO3 (Cu5/Mo0.6‐WO3) for the NO3RR is constructed, which achieves a superior FENH3 of 98.6% and a yield rate of 26.25 mg h−1 mgcat−1 at −0.7 V (vs RHE) in alkaline media, greatly exceeding the performance of Mo0.6‐WO3 and Cu5/WO3 counterparts. Systematic electrochemical measurement results reveal that the promoted activation of NO3− on Cu sites, accompanying accelerated water dissociation producing active hydrogens on Mo sites, are responsible for this superior performance. In situ infrared spectroscopy and theoretical calculation further demonstrate that atomically dispersed Cu sites accelerate the conversion of NO3− to NO2−, and the Mo dopant activates adjacent Cu sites, resulting in the decreased energy barrier of *NO2 to *NO and the stepwise hydrogenation processes, making the synthesis of NH3 thermodynamically favorable. This work demonstrates the critical role of tandem active sites at atomic level in enhancing the electrocatalytic NO3− reduction to NH3, paving a feasible avenue for developing high‐performance electrocatalysts.