Electrocatalysis in Li–O₂ battery over single-atom catalyst based on g-C₃N₄ substrate

The development of Li–O₂ battery is severely hindered by the sluggish reaction kinetics of the oxygen electrode. Herein, we perform a first-principles study of single transition metal atom supported on g-C₃N₄ substrate (TM/g-C₃N₄) as potential single-atom catalyst (SAC) in Li–O₂ batteries. Combined electronic analysis and thermodynamic calculations, the electrocatalytic mechanism of TM/g-C₃N₄ SACs in Li–O₂ batteries is elucidated. Due to strong metal-substrate interactions, the TM atom is durably anchored at the unsaturated pyridine N site in the holey g-C₃N₄ substrate, thereby enabling long cycling stability of the oxygen electrode. Among the fifteen candidates studied, Ru/g-C₃N₄ SAC exhibits the lowest discharge and charge overpotentials. This behavior can be attributed to the synergistic effect of the moveable d electrons of Ru and electron-rich N coordinators, which results in significant interfacial charges, metallic electrical conductivity, and large spin magnetic moments of the RuN₂ active center. This study provides in-depth atomic and electronic insights into the catalytic mechanism of TM/g-C₃N₄ SACs in Li-O₂ batteries.