Study of oxygen reduction reaction on binuclear-phthalocyanine with Fe-Fe, Co-Co, and Fe-Co dual-atom-active sites using density functional theory

Although the N4-macrocyclic ligands have been used to develop single-atom catalysts (SACs), their utilization for the construction of dual-atom catalysts (DACs) for electrocatalytic oxygen reduction reaction (ORR) is poorly investigated. Herein, a binuclear phthalocyanine (bN-Pc) was explored as a theoretical model for the construction of FeFe-bN-Pc, CoCo-bN-Pc, and FeCo-bN-Pc dual-atom-site configurations and their ORR activity along with mechanisms were investigated systematically in alkaline media, using density functional theory (DFT) calculations. The results indicated that the dual-atom-bN-Pc models, having close proximity between adjacent metals, invited individual O-atom of O2 for coordination on both sites, forming a cis-bridged-O2 adduct. The Gibbs free energy studies showed that the decomposition of O2 on dual-atom sites was the rate-determining step, and the Fe-Co-bN-Pc had a lower energy barrier (0.591 eV) for this step as compared to Fe-Fe-bN-Pc (0.641 eV) and Co-Co-bN-Pc (0.692 eV), which justifies its stronger ORR performance. The synergistic effect of Fe-Co collaboration, the close proximity of Fe-Co, and the significant e- donation from the 3d-orbital of active sites into the *orbital of O2 can be attributed to this decrease in limiting the potential for the rate-determining step on Fe-Co-bN-Pc. For future ORR electrocatalysts, this work offers a scientific and engineering perspective on the construction of dual-atom active sites employing molecular moieties.