Active Site Evolution under Working Conditions in Fe−Co Dual-Atom Electrocatalyst

Single-site catalysis plays a central role in electrochemical applications, where the activity critically depends on the local coordination and dynamic evolution of the active sites under operating conditions. Using the FeCo–N3O3@C dual-atom catalyst (DAC) as a model system, we combined density functional theory calculations and microkinetic modeling to investigate its performance in the oxygen evolution (OER) and oxygen reduction (ORR) reactions and to demonstrate the importance of the evolution of the structure of the catalyst under working conditions. Our results reveal that while OER proceeds on the Co site of the as-prepared catalyst, the ORR occurs on a different, dynamically formed active site. Under reaction conditions, water dissociates to yield a stable Co–OH adduct that blocks the Co site for ORR, thereby shifting activity to the Fe center. This restructuring reconciles theory with experiment and explains the high bifunctional performance of FeCo–N3O3@C. The computed polarization curves accurately reproduce the experimental OER and ORR behavior, demonstrating the necessity of explicitly simulating electrochemical conditions rather than relying solely on static Gibbs free energy diagrams. Analysis of Co and Fe K-edge XANES spectra and Bader charge variations further supports the proposed mechanism. Overall, this study highlights the importance of considering the evolution of single- and dual-site catalysts under working conditions and the synergistic interaction between neighboring Fe and Co atoms. Such insights advance our understanding of dynamic catalytic behavior and provide guidance for the rational design of efficient SAC and DAC systems.