Potential-Dependent Oxygen Reduction on FeN₄ under Explicit Solvation Environment

Atomically dispersed FeN4 catalysts have been considered promising materials to replace the expensive Pt-based catalysts for oxygen reduction reaction (ORR), the development of which requires a fundamental understanding of the mechanism underlying their catalytic activity. Herein, we simulate the potential-dependent ORR process via density functional theory calculations and find that the O2 adsorption step becomes the rate-determining step (RDS) at slightly higher applied voltages and the onset potential is 0.8 V, which is because the substrate (*) and *OH intermediates are stabilized at constant potential states (CPS), yet the O2 adsorption becomes thermodynamically unfavorable compared to that at neutral charge states (NCS). The weakened O2 adsorption is attributed to the adjusted Fermi level at CPS that broadens the density of state distribution of the Fe 3d orbital. The determined RDS and the onset potential of ORR over FeN4 by performing potential-dependent simulations agree well with experimental findings, which improves the understanding of the ORR catalytic activity at applied potentials.