Ligand Modulation Induced Spin-State Transition Enhances Oxygen Electrocatalysis in Co Single-Atom Catalysts

Understanding the regulation of metal spin states by the intrinsic properties of coordinating ligands is essential for advancing magnetic single atom catalysts (SACs). However, the fundamental relationship among ligand electronic structure, metal spin configuration, and catalytic performance remains insufficiently established. Here, a combination of grand-canonical density functional theory and microkinetic simulations is employed to demonstrate that increasing ligand conjugation progressively reduces the crystal field splitting energy of Co centers, thereby stabilizing a transition from low spin to high spin configurations. This spin state conversion reshapes the binding characteristics of oxygenated intermediates and leads to concurrent enhancement of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) activities. Guided by this principle, a Co based single atom catalyst featuring a high spin Co site is identified and exhibits an ORR half-wave potential of 0.96 V together with an OER overpotential of 150 mV at 10 mA/cm 2 in alkaline media. These findings establish a clear and general design principle for the rational development of high activity magnetic single atom catalysts for Co-based bifunctional oxygen electrochemistry.