Interfacial Control in Cu–MXene Hybrids Enables Selective NOx‐to‐NH ₃ Electroconversion: A Critical Review

ABSTRACT Electrochemical conversion of nitrogen oxides (NO _x , mainly NO and NO ₂ ) to ammonia (NH ₃ ) transforms a pollutant into a valuable chemical, providing a direct link between emissions control and low‐carbon NH ₃ production under mild conditions. However, NO _x reduction competes with hydrogen evolution (HER) and can diverge to N ₂ /N ₂ O, 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 NO _x ‐to‐NH ₃ electroconversion. The review provides a comprehensive analysis of intermediates and performance, quantifying using device‐relevant metrics (Faradaic efficiency, NH ₃ yield/partial current, energy efficiency, durability, and selectivity against N ₂ /N ₂ O 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 NO _x upcycling into green ammonia.