Interfacial Control in Cu-MXene Hybrids Enables Selective NOx-to-NH3 Electroconversion: A Critical Review.

Electrochemical conversion of nitrogen oxides (NOx, mainly NO and NO2) to ammonia (NH3) transforms a pollutant into a valuable chemical, providing a direct link between emissions control and low-carbon NH3 production under mild conditions. However, NOx reduction competes with hydrogen evolution (HER) and can diverge to N2/N2O, while many catalysts restructure under bias, making results difficult to compare and design rules hard to extract. Cu-MXene hybrids are emerging as a compelling platform because the 2D interface can be engineered to control adsorption, electron (e-) transfer, and local proton (H+) activity through Cu speciation (single sites, clusters, oxides, reconstructed surfaces) and MXene terminations/defects. This critical review summarizes the interfacial control of these catalysts to achieve selective NOx-to-NH3 electroconversion. The review provides a comprehensive analysis of intermediates and performance, quantifying using device-relevant metrics (Faradaic efficiency, NH3 yield/partial current, energy efficiency, durability, and selectivity against N2/N2O and HER). Special emphasis is placed on reactor design, including flow-cell and gas-diffusion electrode (GDE) configurations, which enhance mass transport, stabilize the three-phase boundary, and enable long-term operational stability. Finally, the review emphasizes the use of in situ/operando methods to investigate the reaction mechanisms, outlines design rules and scale-up priorities for practical NOx upcycling into green ammonia.