Insights into the origin of Co-based bimetallic catalysts with a para-structure exhibiting ORR and OER bifunctional activities

Abstract

The development of non-precious metal catalysts with oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) bifunctional activities is of great significance for the development of fuel cells. In this work, the ORR and OER properties of Co-based bimetallic catalysts with a para-structure were studied using density functional theory. In addition, the detachment distance of the active site after the adsorption of intermediates was studied to confirm the stability. The results indicated that G-CoFeN₆ shows the best performance with ORR and OER overpotentials of 0.229 V and 0.312 V, respectively. In addition, the different reaction pathway of G-CoZnN₆ where O₂ is adsorbed on two active sites was analyzed in detail, and it was found that the optimal reaction pathway achieves an ultra-low ORR overpotential of 0.114 V and an OER overpotential of 0.254 V. Notably, the reason why O is always a key factor affecting activity was revealed for the first time. It was found that the bifunctional activity of the catalyst arises from the high d-band center (greater than −2.2 eV) and the suitable spin magnetic moment (0.7μ_B–1.5μ_B). Finally, it was found that the smaller the number of atoms of the adsorbed substance, the greater the effect of adsorption bond length on the adsorption free energy, which not only provides new insights for the study of the ORR or OER, but also provides a reference for other catalytic reactions.