Effect of Metal-Metal Distance on the Performance of Dual-Atom Catalysts for the Oxygen Reduction Reaction: A Density Functional Theory and Micro-kinetics Study.

Dual-atom catalysts (DACs) display excellent activity for the oxygen reduction reaction (ORR). The dual-metal configuration allows for synergistic interactions and tailored adsorption of key intermediates, thereby breaking traditional OH-OOH scaling relations and enabling dissociative O activation pathways. Recent studies suggest that the metal-metal (M-M) distance within DACs critically influences their electronic structure and catalytic behavior; however, a deep understanding of M-M distance effects on ORR thermodynamics and kinetics is presently lacking. Herein, density functional theory (DFT) calculations and microkinetic modeling are performed on 108 DACs with varied M-M distances (2.2-3.5 Å). Moderate M-M distances (≈3 Å) are found to weaken OH binding, lower the OH-OOH scaling slope, and promote bridging O adsorption for facile dissociation. The dissociative pathway lowered the effective scaling relation from ≈3.2 to 2.72 eV, approaching the theoretical value of 2.46 eV. Micro-kinetic simulations identified O activation as the rate-determining step during ORR, with DACs possessing a M-M distance ≈3 Å exhibiting the highest turnover frequencies, due the effective balancing of active-site availability and O activation efficiency. These findings highlight the key role of M-M distance in controlling ORR activity, guiding the design of next-generation DACs with improved efficiency.