Interfacial Charge Reconfiguration Decouples Tandem Kinetics of Dilute Nitrate Electroreduction for Ammonia Recovery

Electrocatalytic nitrate reduction provides a sustainable pathway for coupling wastewater treatment with green ammonia synthesis. However, applications under dilute conditions are restricted by mass transport limitations, hydrogen scarcity, and mismatched tandem kinetics. In this study, a CoMoO4/Cu2O heterostructured electrocatalyst was constructed on copper foam to decouple these tandem pathways. Specifically, Cu2O activates NO3- into *NO2, while CoMoO4 drives the subsequent hydrogenation of *NO2. An interfacial built-in electric field facilitates spontaneous electron transfer from Co to Cu, optimizing the local charge distribution and lowering the water dissociation barrier to 0.36 eV. This synergy accelerates *NO2 conversion and strictly suppresses the accumulation of the toxic NO2- intermediate. At 100 mg L-1 NO3--N and -0.3 V vs RHE, the catalyst achieved a 95.7% conversion efficiency, 94.9% ammonium selectivity, and 90.2% Faradaic efficiency. Furthermore, nitrate-spiked surface water containing 30 mg L-1 of NO3--N was treated in a continuous-flow reactor with membrane capture. With the addition of 0.1 M Na2SO4, 99.7% NO3--N conversion and 94% NH4+-N recovery were achieved. Techno-economic analysis shows a projected net economic benefit of US $ 3.28 kg-1 of NO3--N relative to the selected disposal benchmark. This study establishes a robust paradigm for the deep purification and upcycling of dilute nitrate.