Highly efficient electrochemical ammonia synthesis via nitrate reduction over metallic Cu phase coupling sulfion oxidation.

Electrochemical nitrate reduction reaction (NO 3 RR) is a promising technology for ammonia production and denitrification of wastewater. Its application is seriously restricted by the development of the highly active and selective electrocatalyst and a rational electrolysis system. Here, we constructed an efficient electrochemical ammonia production process via nitrate reduction on the metallic Cu electrocatalyst when coupled with anodic sulfion oxidation reaction (SOR). The synthesized Cu catalyst delivers an excellent NH 3 Faradaic efficiency of 96.0 % and a NH 3 yield of 0.391 mmol h -1  cm -2 at -0.2 V vs. reversible hydrogen electrode, which mainly stem from the more favorable conversion of NO 2 - to NH 3 on Cu 0 . Importantly, the well-designed electrolysis system with cathodic NO 3 RR and anodic SOR achieves a dramatically reduced cell voltage of 0.8 V at 50 mA cm -2 in comparison with the one with anodic oxygen evolution reaction (OER) of 1.9 V. This work presents an effective strategy for the energy-saving ammonia production via constructing effective nitrate reduction catalyst and replacing the OER with SOR while removing the pollutants including nitrate and sulfion.