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

Abstract

The steps of NO₃⁻ adsorption, deoxygenation, nitrogen species hydrogenation and ammonia desorption are vital for electrocatalytic nitrate reduction (NO₃⁻RR) to ammonia, and lowering their Gibbs free energy change (ΔG) is the essential approach for improving NO₃⁻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 ΔG during NO₃⁻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 NO₃⁻RR. According to density functional theory, profited by a strong NO₃⁻ adsorption and a weak NH₃ desorption energy barrier, the optimized CuNi alloy (Cu₃Ni₁/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 Cu₃Ni₁/CF as the cathode material, a novel Zn-nitrate battery exhibits a maximum power density of 5.85 mW cm⁻² with a NH₃ yield of 92.50 μmol cm⁻² h⁻¹ and Faradaic efficiency of 99.15% at 20 mA cm^–2 for NH₃ 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 NO₃⁻RR and Zn-based batteries.

Graphical abstract