Selective Electrochemical NOx Reduction to N2 for Sustainable Ammonia Energy Systems.

Ammonia-based energy systems offer a pathway toward carbon-free energy, yet NOx emissions from ammonia combustion hinder the realization of a sustainable closed-loop. Electrochemical NOx reduction reaction (eNOxRR) provides a promising route to convert NOx to benign N2 under mild conditions. However, under the low NOx concentrations typical of practical exhaust streams, N2 selectivity is limited by competing hydrogenation, hydrogen evolution, and inefficient intermediate utilization. Here, we present a mechanistic perspective on selective NOx-to-N2 conversion, highlighting that eNOxRR proceeds through *NO-mediated pathways with N2O as a key intermediate, while low surface coverage restricts N-N coupling. We propose that integrating tandem catalysis with interfacial microenvironment regulation offers a unified strategy to enhance N2 selectivity. Finally, we outline key challenges for practical implementation under gas-phase and dilute conditions, providing design principles for efficient electrochemical denitrification. This framework has the potential to enable scalable NOx removal and support a closed-loop ammonia energy system.