Unraveling electrochemical oxygen reduction mechanism on single-atom catalysts by a computational investigation

The extension of low-expense and stable electrocatalysts for oxygen reduction reaction (ORR) is of importance to improve the performance of metal-air batteries and fuel cells. In this work, we unravel the ORR electrocatalytical mechanisms on a series of transition metal atom-doped on the defect graphene (TM@sv-graphene) by carrying out spin-polarized first-principles computations. The formation energy of the TM@sv-graphene, which is related to its stability, along with the binding energy of O-2, OOH, 2OH, OH, and O species are evaluated. The calculations of Gibbs free energy show that two different pathways, O* mechanism and 2OH* mechanism, of ORR compete with each other based on the structures of intermediates (OOH, 2OH, OH and O). It is found that Co, Rh, Ir, Pt, and Mn@sv-graphene favor the O* mechanism while Ag, Au, Cd, Cu, Zn, Fe, Ni, Pd, Sc, Cr, Ti, Zr, and V@sv-graphene strongly promote the 2OH* mechanism. The overpotential (eta) of the ORR is predicted and can be a valid descriptor that manifests the catalytic activity of different TM@sv-graphene. Among these catalysts, the Pd@sv-graphene (eta = 1.20 V) exhibits the best activity for the ORR. The results provide new insight into electrochemical mechanism of ORR for novel single-atom electrocatalyst.

Automated summary

The study investigated the electrocatalytic mechanisms of transition metal atom-doped graphene for the oxygen reduction reaction, revealing different pathways based on the structures of intermediates. The overpotential of ORR was predicted with Pd@sv-graphene showing the best activity among the catalysts.