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

Abstract Electrocatalytic NO 3 − reduction to NH 3 is a promising technique for both ammonia synthesis and nitrate wastewater treatment. However, this conversion involves tandem processes of H 2 O dissociation and NO 3 − hydrogenation, leading to inferior NH 3 Faraday efficiency (FE) and yield rate. Herein, a tandem catalyst by anchoring atomically dispersed Cu species on Mo‐doped WO 3 (Cu 5 /Mo 0.6 ‐WO 3 ) for the NO 3 RR is constructed, which achieves a superior FE N H 3 of 98.6% and a yield rate of 26.25 mg h −1 mg cat −1 at −0.7 V (vs RHE) in alkaline media, greatly exceeding the performance of Mo 0.6 ‐WO 3 and Cu 5 /WO 3 counterparts. Systematic electrochemical measurement results reveal that the promoted activation of NO 3 − 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 NO 3 − to NO 2 − , and the Mo dopant activates adjacent Cu sites, resulting in the decreased energy barrier of * NO 2 to * NO and the stepwise hydrogenation processes, making the synthesis of NH 3 thermodynamically favorable. This work demonstrates the critical role of tandem active sites at atomic level in enhancing the electrocatalytic NO 3 − reduction to NH 3 , paving a feasible avenue for developing high‐performance electrocatalysts.