Unraveling the Activity and Mechanism of TM@g-C 4 N 3 Electrocatalysts in the Oxygen Reduction Reaction.

In this work, a high-throughput screening strategy and density functional theory (DFT) are jointly employed to identify high-performance TM@g-C 4 N 3 (TM = 3d, 4d, 5d transition metals) single-atom catalysts (SACs) for the oxygen reduction reaction (ORR). Comprehensive studies demonstrated that Cu@, Zn@, and Ag@g-C 4 N 3 show high ORR catalytic activities under both acidic and alkaline conditions with favorable overpotentials (η ORR ) of 0.70, 0.89, and 0.89 V, respectively; among them, Cu@g-C 4 N 3 is the best candidate. The ORR follows a four-electron mechanism with the final product H 2 O/OH - . Cu@, Zn@, and Ag@g-C 4 N 3 catalysts also exhibit good thermal (500 K) and electrochemical (0.93-3.14 V) stabilities. Cu@, Zn@, and Ag@g-C 4 N 3 demonstrate superior activities with low η ORR due to its moderate adsorption strength of *OH. The η ORR and the Gibbs free energy changes of *OH (Δ G 4 (acidic) /Δ G 4 (alkaline) ) resemble a volcano-type relationship under acidic/alkaline conditions, respectively. Additionally, the O-O bond length in *OOH emerged as an effective structural descriptor for rapidly identifying the promising electrocatalysts. This research provides valuable insights into the origin of the ORR activity on TM@g-C 4 N 3 and offers useful guidance for the efficient exploration of high-performance catalyst candidates.