^* H Species Regulation of Heterostructured Cu ₂ O/NiO Nanoflowers Boosting Tandem Nitrite Reduction for High‐Efficiency Ammonia Production

Abstract Ambient electrocatalytic reduction of NO ₂ ⁻ to NH ₃ (NO ₂ RR) provides a reliable route for migrating NO ₂ ⁻ pollutants and simultaneously generating valuable NH _3. However, the NO ₂ RR involves multistep electron transfer and complex intermediates, rendering the achievement of high NH ₃ selectivity a major challenge. In this contribution, heterostructured Cu ₂ O/NiO nanoflowers are explored for incorporating the advantages of dual active sites as a highly active and selective NO ₂ RR catalyst. Combined theoretical calculations and in situ FTIR/EPR spectroscopy analysis, it is revealed the synergistic effect of Cu ₂ O and NiO to promote the NO ₂ RR energetics of Cu ₂ O/NiO heterostructure electrocatalyst through a tandem catalysis pathway, where Cu ₂ O activates the initial absorption and deoxygenation of NO ₂ ⁻ for boosting ^* NO formation, while the generated ^* NO on Cu ₂ O is then transferred on NiO substrate with abundant active hydrogen for NH ₃ conversion. Moreover, the heterostructure formation enhances ^* H retention capacity, promoting ^* H consumed in NO ₂ RR and inhibiting inter‐ ^* H species binding. As a result, Cu ₂ O/NiO equipped in a flow cell displays a superior NH ₃ 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 NH ₃ production reactions including NO ₃ ⁻ reduction.