Electroreduction-assisted adsorption energy modulation of copper-nickel alloy for nitrate electroreduction to ammonia applied to energy conversion and zinc-nitrate batteries

The steps of NO 3 − adsorption, deoxygenation, nitrogen species hydrogenation and ammonia desorption are vital for electrocatalytic nitrate reduction (NO 3 − RR) to ammonia, and lowering their Gibbs free energy change (Δ G ) is the essential approach for improving NO 3 − RR. The copper-based alloys are considered as the outstanding catalysts thanks to the tunable d-band center, reconstruction and synergistic effect of multiple metal atoms in the past decades. Here, we synthesized a single-phase copper-nickel alloy by electrodeposition and optimized its Δ G during NO 3 − RR through tuning the electrodeposition potential to regulate the metal component ratio. The atomic ratio of Ni/Cu in CuNi alloys is gradually increased as the negative shift of deposition potential from −1.0 to −1.2 V versus SCE, thus achieving the fast modulation of intermediate adsorption energy for NO 3 − RR. According to density functional theory, profited by a strong NO 3 − adsorption and a weak NH 3 desorption energy barrier, the optimized CuNi alloy (Cu 3 Ni 1 /CF) exhibits an ideal ammonia yield of 364.1 μmol cm −2  h −1 and Faradaic efficiency of 92.25% at −0.23 V versus RHE. Further applying Cu 3 Ni 1 /CF as the cathode material, a novel Zn-nitrate battery exhibits a maximum power density of 5.85 mW cm −2 with a NH 3 yield of 92.50 μmol cm −2  h −1 and Faradaic efficiency of 99.15% at 20 mA cm –2 for NH 3 production. This work not only offers a rational design concept with clear guidance for efficient modulation of intermediate adsorption free energy on alloy catalysts prepared by electrodeposition, but also provides the further understanding for efficient developments of NO 3 − RR and Zn-based batteries. Graphical abstract