Self-reducing Cu2O/Cu nanosheet interface for efficient electrocatalytic production of ammonium from nitrate

Electrochemical reduction of nitrate is a promising method to treat nitrogen-containing waste streams, because it can be adapted to enable ammonia production. As widely applied electrocatalysts, Cu-based materials have bottlenecks for practical application due to competitive hydrogen evolution reactions, uncontrollable byproducts and fabrication methods. Herein, nanosheet Cu2O/Cu interface was prepared in-situ by a simple constant-current anodic oxidation method, which completely avoids processes such as complexing agent addition or postfabrication calcination. Formation of the Cu2O/Cu interface was captured with in-situ Raman spectroscopy. Experiments combined with theoretical calculations show that the Cu2O/Cu interface had a high electron cloud density that effectively promoted the fracture of N-O bonds, thereby reducing the generation of intermediates such as *NO2. Moreover, the interface had favorable *H adsorption-desorption properties, which could effectively inhibit HER, thereby achieving high selectivity and Faraday efficiency. The interfacial material achieved 83.6 % nitrate conversion, 93.2 % ammonia Faraday efficiency, and 2793 mu g & sdot;h- 1 & sdot;cm- 2 ammonia yield at operating voltages of -0.45 V (vs RHE) under neutral conditions, exceeding the performance of most copperbased electrocatalysts. By virtue of the micro-reduction environment of the Cu2O/Cu interface in the reaction system, stable catalytic activity is guaranteed and observed for 25 cycle trials.