Potential-Driven Structural Evolution of Single-Atom Rhenium Sites Enables High-Performance Oxygen Electrode Reaction and Rechargeable Zn-Air Battery

The availability of high-quality and durable bifunctional oxygen electrode catalysts remains a significant linchpin for rechargeable zinc-air batteries (ZABs). Modulating the d/f orbitals of isolated single-atom metal sites to enhance the reaction kinetics is an eloquent strategy. Herein, we fabricate a single-atom rhenium catalyst (Re-NG) with Re-N₄ sites on N-doped graphene, which renders exceptional oxygen reduction reaction (ORR) catalytic capacity, delivering a half-wave potential of 0.86 V and excellent oxygen evolution reaction (OER) activity with low overpotential (η₁₀ = 368 mV). Furthermore, the Re-NG performs satisfactorily on the cathode of a rechargeable ZAB with cell voltages as high as 1.53 V and specific capacities as high as 828.7 mA h g_Zn⁻¹, which is close to theoretical value, and outstanding cycling stability. The excellent performance of the Re-NG can be attributed to the structural evolution at different reaction potentials as revealed by in situ X-ray absorption spectrum characterization and theoretical simulations, resulting in the formation of different active sites (ReN₄-O/Re-N₄-2O), which effectively and stably catalyze the reactions, thus accelerating the ORR/OER kinetics and enabling high activity. Our study clearly elucidates the mechanisms by which Re-NGs efficiently catalyze oxygen electrode reactions, providing a valuable reference for the as yet unknown catalytic mechanism of single-atom oxygen catalysts.