Mechanistic Understanding of the Electrocatalytic Nitrate Reduction Activity of Double-Atom Catalysts

Electrochemical nitrate reduction reaction (NO3RR) has promise for both nitrogen pollution management and low-temperature ammonia production instead of the conventional Haber-Bosch process. Nevertheless, it relies on electrocatalysts with controllable reaction pathways and product selectivity. Herein, we design novel homonuclear double-atom catalysts (DACs) supported on N-doped graphene (TM2/N6-G) as potential NO3RR catalysts using first-principles calculations. The results reveal that Cr2/N6-G, Mn2/N6-G, and Cu2/N6-G serve as the most promising NO3RR catalysts, as they exhibit stability, excellent activity, high selectivity (faradic efficiency of >61.28%), and low limiting potentials (-0.46, -0.45, and -0.36 V for Cr2/N6-G, Mn2/N6-G, and Cu2/N6-G, respectively). In addition, multiple-level descriptors and volcano plots provide insight into the origin of NO3RR activity and enable fast prescreening among numerous candidates. Furthermore, considerable potential energy barriers are found in the formation of byproducts NO2, NO, and N2O, validating their high selectivity. The conversion of nitrate to ammonia is more competitive than the hydrogen evolution reaction on Cr2/N6-G, Mn2/N6-G, and Cu2/N6-G possessing a lower limiting potential. This study provides a guideline for the rational design of highly active, selective, and durable electrocatalysts in NO3RR.