Cu/NiO nanorods for efficiently promoting the electrochemical nitrate reduction to ammonia

The electrochemical nitrate reduction reaction (ENO₃RR) is a green ammonia synthesis method under ambient conditions relative to the traditional Haber-Bosch technology, which does not require high-temperature or high-pressure conditions and can convert nitrate pollutants in the environment into value-added NH₃, thus achieving a dual purpose. However, more electrocatalysts with a remarkable performance towards high-efficiency ENO₃RR need to be developed. In this work, a Cu/NiO-NF composite electrocatalyst with a nanorod structure on nickel foam was successfully fabricated, which contains heterogeneous interfaces between Cu and NiO toward selective electrocatalytic nitrate reduction for ammonia synthesis. The steric nanorod morphology of the catalyst can significantly increase the surface area, expose more active sites, and improve the reaction activity. Moreover, the construction of the composite and the interface effectively boosts the synergistic effect of the active species Cu and NiO, which can regulate the electronic structure of the catalyst, expose more active sites, enhance the conductivity of the material, and accelerate the interfacial electron transfer, thereby further promoting the ENO₃RR performance. This Cu/NiO-NF composite exhibits a high NH₃ yield of 0.6 mmol h^-1 cm^-2 and up to 97.81% faradaic efficiency at the optimal applied potential of -1.0 V (vs. RHE) in a concentration of 0.1 M NO₃^--containing 0.1 M PBS. Furthermore, it demonstrates excellent electrochemical cycle stability. This work provides insights into the rational design and fabrication of ENO₃RR electrocatalysts for potential electrocatalytic applications.