Mechanistic Understanding\nof the Electrocatalytic\nNitrate Reduction Activity of Double-Atom Catalysts

Abstract

Electrochemical nitrate reduction\nreaction (NO₃RR) has\npromise for both nitrogen pollution management and low-temperature\nammonia production instead of the conventional Haber–Bosch\nprocess. Nevertheless, it relies on electrocatalysts with controllable\nreaction pathways and product selectivity. Herein, we design novel\nhomonuclear double-atom catalysts (DACs) supported on N-doped graphene\n(TM₂/N₆-G) as potential NO₃RR catalysts\nusing 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\nselectivity (faradic efficiency of >61.28%), and low limiting potentials\n(−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\nand volcano plots provide insight into the origin of NO₃RR activity and enable fast prescreening among numerous candidates.\nFurthermore, considerable potential energy barriers are found in the\nformation of byproducts NO₂, NO, and N₂O, validating\ntheir high selectivity. The conversion of nitrate to ammonia is more\ncompetitive than the hydrogen evolution reaction on Cr₂/N₆-G, Mn₂/N₆-G, and Cu₂/N₆-G possessing a lower limiting potential. This study\nprovides a guideline for the rational design of highly active, selective,\nand durable electrocatalysts in NO₃RR.