^* 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.