Different Bonding Defects on Dual-Metal Single-Atom Electrocatalyst CoZnN₆ (OH) for Oxygen Reduction Reaction

Since dual-metal single-atom catalyst (CoZnN/C) has been experimentally synthesized by atomically arching CoZn on N-doped carbon nanofibers and exhibited potential electrocatalysis activity towards oxygen reduction reaction (ORR), we perform first-principles calculations to identify the highly active sites at different defects by comparing the four-step ORR processes on the constructed four CoZnN₆ models on graphene. The corresponding N-edge effect, dopant effect, and C-edge ring-closing effect are evaluated with the ORR evolution on different bonding environments, including pristine CoZnN₆ (OH), nanoribbon (NR) along zigzag direction, substitution of carbon/oxygen (C/O substitution), and C-edge ring-closing configurations. OH-ligand is shown to significantly improve the ORR activities for all the considered structures. Especially, C-substituted CoZnN₆ (OH), NR-CoZnN₅ O(OH) and CoZnN₆ (OH) with C-edge-effect exhibit obviously reduced overpotentials (η_lim =0.28, 0.48 and 0.41 V) of rate-determining steps among all the considered nine candidates. By plotting the relationship between the limiting potentials (U_lim ) and free energies of intermediate *OH (ΔG_OH* ), two prior catalysts of pristine-CoZnN₅ C(OH) and defect-CoZnN₆ CH(OH) are located near the top of the volcano curve with higher U_lim =0.95 and 0.82 V than Pt(111) (U_lim =0.80 V), implying that C-substitution could facilitate ORR performance in pristine- and defect-CoZnN₆ (OH) bonding situation.