Theoretical characterization of sulfur and nitrogen dual-doped graphene

We have employed density functional theory to unravel the structural and electronic properties of sulfur and nitrogen dual-doped graphene. In the preferred configuration, the sulfur and nitrogen atoms replace the carbon atoms of a CC bond, but they are not bonded. Thus, the nitrogen atom adopts a pyridinic arrangement and the sulfur atom an edge like bonding pattern, since it is solely bonded to two carbon atoms. The formation energy determined for sulfur and nitrogen dual-doped graphene was 1.36 eV smaller than the sum of the formation energies (FE) of sulfur doped graphene and nitrogen doped graphene. There is a synergic effect between sulfur and nitrogen which lowers the FE as compared with separated doping. This particular arrangement of the dopants enhances the reactivity of the sheet. For example, it facilitates the addition of molecular oxygen to sulfur to form SO2 functionalities. In general, the introduction of sulfur and nitrogen opens a band gap as indicated by HSE calculations.