Dual-Atom Catalysts for the Oxygen Reduction Reaction: Unraveling Atomic Structures under Reaction Conditions.

Metal-nitrogen-carbon (M-N-C, M = Mn, Fe, Co, Ni, Cu, Zn, and Pt) dual-atom catalysts (DACs) show great potential for the oxygen reduction reaction (ORR) at the cathode of proton exchange membrane fuel cells (PEMFCs). During catalytic reactions, multiple reactants and intermediates interact with the active sites, yet understanding their dynamic structural evolution under the operating conditions remains challenging. In this study, we analyze 186 heteronuclear FeM-N-C DACs using ab initio thermodynamic phase diagrams and find that OH-ligated structures become predominant at higher applied potentials. This indicates that catalytic activity is governed by electrochemically modified metal sites rather than by the bare structures. We further investigate the catalytic mechanism of these ligated structures and reveal that the ORR limiting potential can be efficiently predicted from the phase diagrams. Among the 186 DACs studied, 29 were found to outperform Pt-based catalysts, with FeCo-N-C DACs demonstrating the highest activity. Our computational predictions align well with experimental observations, highlighting the crucial role of dynamic structural changes under reaction conditions in enhancing the electrocatalytic performance of DACs.