Functional group combination synergistically regulates the selectivity of 2/4e-ORR in carbon catalysts

Precise regulation of oxygen reduction reaction (ORR) for 2e-ORR or 4e-ORR is of great importance in designing efficient catalysts for electrochemical reactions. Currently, the exact roles of the functional groups and their possible synergistic functions still remain controversial. In this work, catalysts with different combinations of N and O functional groups were prepared using graphite to regulate ORR selectivity. Meanwhile, the quantum chemical parameters of various functional group combinations in the literature were summarized by using DFT calculation, and a method was provided to explain the relationship between functional group combinations, electronic structure and ORR selectivity by HOMO orbital delocalization index (ODI H ) and Mulliken population (MP). Finally, combining the molecular level calculations, a close correlation between the molecular structures with the tendency of 2e-ORR or 4e-ORR was established. Among them, the combination of C=O, N-Graphitic and Pyridinic-Pyrrolic-Graphitic nitrogen structure promoted 4e-ORR. C-O, O=C-O, N-Pyridinic and N-Pyrrolic promoted 2e-ORR. This study has revealed the essential difference between 2e-ORR and 4e-ORR, and provided a direction for determining the structure of 2e-ORR or 4e-ORR catalysts.