Electrochemical nitrate reduction for ammonia production: amorphous or crystalline oxidized copper catalyst?

The electrochemical nitrate reduction reaction (NO3RR) is a promising approach to remove environmental pollutants while producing ammonia (NH3) under ambient conditions. Oxidized copper (O-Cu) with crystal structures has been widely investigated for NO3RR performance; however, its amorphous counterpart has rarely been explored. An amorphous oxidized copper (a-O-Cu) is designed to evaluate its NO3RR performance along with a control sample of crystalline oxidized copper (c-O-Cu) for comparison. At an applied potential of -0.53 V vs. RHE, a-O-Cu delivered an NH3 selectivity of 93.6% and an FE of 84.9%, which are 1.1 and 1.3 times higher than those of c-O-Cu, respectively. Density functional theory (DFT) calculations reveal that the enhanced NO3RR performance of a-O-Cu is mainly attributed to its high water dissociation capability and amorphous structure-enabled high catalytic activity. The strategy demonstrated here can be extended to design other efficient metal-based amorphous electrocatalysts for NO3RR and C-N coupling reactions. An amorphous oxidized copper (a-O-Cu) is designed to investigate for electrochemical nitrate reduction to ammonia. It is found that a-O-Cu has high capability for water dissociation and amorphous structure-enabled high catalytic activity.