Mechanistic study of Eu single atoms occupying four vacancy centers as potential electrocatalysts for the oxygen reduction reaction

The oxygen reduction reaction (ORR) on the oxygen electrode plays a critical role in rechargeable metal-air batteries, and the development of electrochemical energy storage and conversion technologies for the ORR is of great significance. In this study, the catalytic performance of rare earth-doped graphene (EuNxC6-x-Gra) as an electrocatalyst for the ORR was investigated. The results showed that a majority of the catalysts exhibited good ORR catalytic activity under acidic conditions, with some approaching or even surpassing commercial Pt-based catalysts (ηORR = 0.45 V). Particularly, EuN2C4-2-Gra demonstrated an ηORR of 0.38 V. It has been observed that the f-band center of Eu atoms increases with an increasing number of N atoms, and the charge distribution exhibits a "U" shape. There is a decreasing trend from N0 to N3 and an increasing trend from N4 to N6. By incorporating the proportional relationship of the adsorption free energies of reaction intermediates (ΔG*ads), a volcano diagram was constructed to rapidly assess catalytic activity. Finally, an intrinsic characteristic descriptor φ was formulated to quantitatively describe the relationship between φ and ηORR, providing a new tool for predicting and designing catalysts. This will provide guidance for the development and design of high-performance rare earth single atom catalysts.