*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 NH3. 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.