Dynamic Evolution of Cu ₂ O-CuO/Cu Electrocatalyst for Ammonia Synthesis by Electrocatalytic Nitrate Reduction

Electrocatalytic nitrate reduction (eNO 3 RR) is a promising alternative to the Haber–Bosch process for ammonia production. Besides, it can transform and utilize the nitrate in waste water. Copper catalysts are widely employed; however, they exhibit weak binding affinity for most reaction intermediates, and their weak hydrogen binding energy limits the hydrogenation of these intermediates, thereby affecting both the reaction activity and ammonia selectivity. In this study, a two-step electrochemical synthesis method was used to sequentially load CuO and Cu 2 O onto the Cu foam surface to make a Cu 2 O-CuO/Cu heterostructure. Combination of in situ FTIR and Raman spectra confirmed that the synergistic effect of Cu 2 O and CuO promoted the eNO 3 RR efficiency. This synergy effectively enhanced the binding affinity of reaction intermediates, where Cu 2 O facilitated NO 3 – adsorption and catalyzed its conversion to *NO 2, while CuO aided in water splitting to enhance active hydrogen availability. Density functional theory (DFT) calculations showed that Cu 2 O-CuO/Cu efficiently lowered the energy barrier for the steps from *NO 2 H to *NO and from *NH 2 OH to *NH 2 . Moreover, the reaction involved a significant dynamic evolution among Cu II, Cu I, and Cu 0, which enhanced the generation and consumption of reaction intermediates. At –0.7 V vs RHE, Cu 2 O-CuO/Cu resulted in a high ammonia yield of 60.5 mg h –1 cm –2 with a Faradaic efficiency (FE) of 98.7% and sustained a current density reaching 1.14 A cm –2 . This work reveals the dynamic evolution of electrocatalysts and presents an efficient strategy for construction of electrocatalysts with synergistic Cu-based heterostructures.