▎ 摘　　要

Transition metal oxides (TMOs) anchored on a carbon nanostructure have been widely pursued for oxygen reduction reaction (ORR) catalysis. The high ORR activity of TMO/graphene has been often attributed to the synergistic nature between TMO and carbon but with little relevant mechanistic study. In this report, the focus is made on how the type of majority oxygen-containing functional group of graphene affects the ORR performance of the resulting TMO/graphene nanocomposites. Our TiO2/carboxylated graphene and ZrO2/hydroxylated graphene rendered an ORR activity very close to that of Pt/C with an equal mass loading, via a four-electron transfer dominant process unlike other TMO/graphene variants of study. It is revealed that a stable anchoring of nanoparticles (NPs) on the graphene surface, which is essential to prevent the restacking of graphene layers, is established only through a specific type of functional groups on the graphene. In addition, the interplay among TMOs, graphene, and functional groups is found to be deterministic in the activity and electron transfer pathway of ORR, which is supported by density function theory (DFT) calculations. The calculations indicate that the electron transfer pathway is dependent upon the structure of NPs interfacing with functional groups of the graphene as it affects the preferred sites for oxygen dissociation.