Constructing Cu-CuO heterostructured skin on Cu cubes to promote electrocatalytic ammonia production from nitrate...

Electroreducting nitrate (NO₃^-) into ammonia (NH₃), i.e. NO₃^-RA, can not only relieve NO₃^- pollution but also produce high value-added NH₃. Cu-based species have been taken as a promising catalyst for NO₃^-RA because of their relatively high Faradaic efficiency (FE), benefiting from the weak side hydrogen evolution reaction (HER). However, their NH₃ yield rates are still unsatisfactory due to the multiple electron paths of NO₃^-RA. Herein, we report a Cu cube with Cu-CuO heterostructured skin, prepared by electrochemically induced reconstruction from a Cu₂O cube. This novel Cu-based catalyst presents a mol-level NH₃ yield rate of 3.17 mol h^-1 g^-1 ranking at the top level among non-noble metal catalysts and an ultrahigh FE of 98.7 %. These excellent performances attribute to the Cu-CuO heterostructured skin of Cu cubes, which has favorable energy for the hydrogenation of *NO to *NOH during the NO₃^-RA process and an unfavorable one for HER. For the NO₃^- removal of real river water, this novel Cu-based catalyst presents a high NO₃^- removal rate of 95.5 % after the NO₃^-RA test for 12 h, resulting in a lower NO₃^- concentration than the maximum residual amount of NO₃^- in drinking water limited by WHO and China. This study provides a feasible strategy by the electrochemical reconstruction method to prepare superior Cu-based electrocatalysts with mol-level NO₃^-RA performances for the purification of nitrate wastewater.