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/Mo_0.6-WO₃) for the NO₃RR is constructed, which achieves a superior FE_NH3 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-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.