Underlying Electrochemical Activity Mechanisms on Tunable Electronic Structures of Graphene Quantum Dots Doped with Nitrogen and Sulfur Heteroatoms

Doping heteroatoms into graphene quantum dots (GQDs) is an efficient way to tune electronic structures. Herein, electronic mechanism of GQDs doped with N and S is studied by density functional theory (DFT). The formation energies, electronic structures, and electrostatic potentials of pristine and co-doped GQDs are calculated to reveal effects of different doping types on electronic properties. The geometry configuration of N and S bonding groups also plays an important role in tuning electronic structures of doped GQDs. The synergistic effect of N and N/S co-doping is mainly to reduce the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) gap of the GQD structure. It is found that the introduction of S-containing groups can enhance positive area around N and increase atomic charge density of C atoms connected to N, which indicates that heteroatom co-doped GQDs have improved electron transports and can tune their electronic properties. In order to understand their oxygen reduction reaction (ORR) mechanisms, oxygen adsorption energies are calculated based on different structures of doped GQDs. Therefore, this work will provide valuable information on understanding the relationship between heteroatom dopants and electronic properties of N/S co-doped GQDs for the applications in nanoelectronic devices.