*H Species Regulation of Heterostructured Cu2O/NiO Nanoflowers Boosting Tandem Nitrite Reduction for High-Efficiency Ammonia Production

Abstract

Ambient electrocatalytic reduction of NO₂⁻ to NH₃ (NO₂RR) provides a reliable route for migrating NO₂⁻ pollutants and simultaneously generating valuable NH_3. However, the NO₂RR involves multistep electron transfer and complex intermediates, rendering the achievement of high NH₃ selectivity a major challenge. In this contribution, heterostructured Cu₂O/NiO nanoflowers are explored for incorporating the advantages of dual active sites as a highly active and selective NO₂RR catalyst. Combined theoretical calculations and in situ FTIR/EPR spectroscopy analysis, it is revealed the synergistic effect of Cu₂O and NiO to promote the NO₂RR energetics of Cu₂O/NiO heterostructure electrocatalyst through a tandem catalysis pathway, where Cu₂O activates the initial absorption and deoxygenation of NO₂⁻ for boosting ^*NO formation, while the generated ^*NO on Cu₂O is then transferred on NiO substrate with abundant active hydrogen for NH₃ conversion. Moreover, the heterostructure formation enhances ^*H retention capacity, promoting ^*H consumed in NO₂RR and inhibiting inter-^*H species binding. As a result, Cu₂O/NiO equipped in a flow cell displays a superior NH₃ yield rate of 128.2 mg h⁻¹ cm⁻² and Faradaic efficiency of 97.1% at a high current density of −1.25 A cm⁻². Further, this designed tandem system is proven to be adaptable for other electrochemical NH₃ production reactions including NO₃⁻ reduction.