Electrocatalytic nitrate reduction to ammonia over Cu/Cu2O catalysts with controllable ratios

Considering the background of low carbon emission and environmental protection, the development of electrocatalysts for efficient nitrate reduction to ammonia (NRA) has recently attracted increasing attention. Cu/Cu2O has been widely adopted as an efficient catalyst for the NRA reaction. However, the preparation of Cu/Cu2O with controllable ratios remains a challenge. Herein, a series of Cu/Cu2O were prepared through thermal decomposition of copper nitrate on the surface of hydrothermal carbon (HTC) under different temperatures. The ratios of Cu to Cu2O gradually increased with increasing calcination temperature. The effect of the Cu/Cu2O ratio on the NRA activity was investigated. The Cu/Cu2O/HTC-350 catalyst achieved the optimum NRA performance (Faradaic efficiency: 89.5%, ammonia selectivity: 81.7%). Further research demonstrated that the low energetic barrier for supplying electrons from the catalyst surface to the adsorbed reactant and the fastest electron transfer rate were beneficial for the nitrate electroreduction to ammonia. The electrochemical quasi in situ electron spin resonance (ESR) experiments proved the positive effect of active hydrogen (*H) during NRA process. This study provides a new avenue for the preparation of efficient Cu/Cu2O with controllable ratio catalysts for NRA reaction.