Interaction and Quantum Capacitance of Nitrogen/Sulfur Co-Doped Graphene: A Theoretical Calculation

The interaction between different configurations of nitrogen and sulfur, as well as the influence on the quantum capacitance of N/S co-doped graphene. was investigated by applying density functional theory calculations. It was found that the sulfur atom tends to dislocate from the graphene plane in the presence of a pyrrolic-N atom. However, in the presence of pyridinic-N, the sulfur atom maintains its sp2 hybridization in both 6- and 5-membered rings. Moreover, at low concentration, sulfur doping produces a new state close to the Fermi level, which enhances the maximum quantum capacitance of the co-doped graphene up to 50%. Nevertheless, there is no further improvement when another nitrogen or sulfur atom was embedded into the co-doped graphene.