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

Abstract

<p>Electrocatalytic nitrate reduction reaction (NO₃RR) is a promising approach for converting nitrate into environmentally benign or even value-added products such as ammonia (NH₃) using renewable electricity. However, the poor understanding of the catalytic mechanism on metal-based surface catalysts hinders the development of high-performance NO₃RR catalysts. In this study, the NO₃RR 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 NO₃RR toward NH₃, 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 NO₂, NO, N₂O, and N₂ 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 NH₃ production by MXene-based SACs electrocatalysts under ambient conditions but also provide insights for the development of next-generation NO₃RR electrocatalysts.</p>