Oxygen vacancy-mediated Bi-CuO_x heterostructure for enhanced electrochemical nitrate-to-ammonia production and Zn-nitrate battery behavior

Electrochemical nitrate reduction to ammonia (NRA) is an emerging sustainable technology that converts nitrate contamination in wastewater into the value-added chemical ammonia. Copper-based catalysts represent one of the most competitive non-noble NRA electrocatalysts due to their robust nitrate adsorption capability. In this study, we developed a series of Bi-Cu bimetallic oxides (BiCuO_x) with mixed oxidation states of Cu and Bi by tuning the surface oxygen vacancy (O_V) content via a one-pot solution-based in situ H*-mediated reduction method. The resulting BiCuO_x catalyst exhibits an enlarged surface area, abundant electrochemically active sites, and optimized O_V concentration, delivering a high NH₃ faradaic efficiency (FE) of 92.27% ± 3.47% and an NH₃ yield rate of 4331.25 ± 208.4 μg h⁻¹ mg_cat.⁻¹ at −0.8 V vs. RHE. Theoretical calculations reveal that the as-obtained BiCuO_x catalyst more effectively suppresses NO₂* intermediate poisoning on its surface compared to the single-component Cu catalyst owing to the favorable orbital hybridization between the intermediates and the catalyst surface, thereby facilitating the subsequent steps in the NRA reaction pathway. Furthermore, a zinc-nitrate battery is designed by integrating a BiCuO_x cathode with a zinc plate anode sourced from spent zinc-carbon batteries, achieving a peak power density of 1.706 mW cm⁻² and an NH₃ FE of 82.31%. This study highlights a low-cost and highly active oxygen vacancy-mediated catalyst for electrochemical NRA through one-pot solution synthesis, promoting green ammonia production via sustainable NRA.