Effects of Hydronium and Hydroxide Ion/group on Oxygen Reduction Reaction Electrocatalytic Activities of N-doped Graphene Quantum Dots

In this work, density functional theory (DFT) is used to investigate the effects of different forms of H3O+, OH-, H3O and OH on oxygen reduction reaction (ORR) electrocatalytic properties of graphene quantum dots (GQDs). The ORR catalytic activity can be enhanced by ligand functionalization of graphitic N-doped GQDs (gN-GQDs) with H3O and OH. The electrocatalytic activities of different ions/groups on GQDs are different for the presence of ions/groups can rearrange the electronic structure of doped GQDs. The ORR overpotentials of gN-GQDs with H3O+, OH-, H3O and OH are 1.49, 1.80, 0.69, and 0.83 V, respectively. The findings indicate that the adsorption of H3O on the surface of gN-GQDs has the best ORR catalytic performance and can effectively promote oxygen reduction reactions. Analyzing differential electron density illustrates that when H3O is adsorbed to gN-GQDs, the adsorption electron transfer of O2 is more obvious to facilitate the adsorption of O2. The results can reveal the influences of different ions/groups on ORR catalytic mechanisms of GQDs and provide guidance for the design of ORR electrocatalysts.