Unraveling the Performance Descriptors for Designing Single‐Atom Catalysts on Defective MXenes for Exclusive Nitrate‐To‐Ammonia Electrocatalytic Upcycling

Abstract Electrocatalytic nitrate reduction reaction (NO 3 RR) is a promising approach for converting nitrate into environmentally benign or even value‐added products such as ammonia (NH 3 ) using renewable electricity. However, the poor understanding of the catalytic mechanism on metal‐based surface catalysts hinders the development of high‐performance NO 3 RR catalysts. In this study, the NO 3 RR mechanism of single‐atom catalysts (SACs) is systematically explored by constructing single transition metal atoms supported on MXene with oxygen vacancies (O v ‐MXene) using density functional theory (DFT) calculations. The results indicate that Ag/O v ‐MXene (for precious metal) and Cu/O v ‐MXene (for non‐precious metal) are highly efficient SACs for NO 3 RR toward NH 3 , with low limiting potentials of −0.24 and −0.34 V, respectively. Furthermore, these catalysts show excellent selectivity toward ammonia due to the high energy barriers associated to the formation of byproducts such as NO 2 , NO, N 2 O, and N 2 on Ag/O v ‐MXene and Cu/O v ‐MXene, effectively suppressing the competitive hydrogen evolution reaction (HER). The findings not only offer new strategies for promoting NH 3 production by MXene‐based SACs electrocatalysts under ambient conditions but also provide insights for the development of next‐generation NO 3 RR electrocatalysts.