DFT calculation for stability and quantum capacitance of MoS2 monolayer-based electrode materials

The stability, electrical properties and quantum capacitance of Ti, Au, Ag, Cu, Al, B, N, and P doping pristine and single-vacancy VS MoS2 monolayer have been studied by using the first-principles methods. These doped atoms form strong bonds with MoS2, and the optimized structures exhibit metallicity. MoS2 monolayer has a high double layer capacitance due to its high specific surface area. However, it has low quantum capacitance hindering its application in supercapacitors. This is attributed to the confinement of the electron density of states near Fermi level of pristine MoS2 monolayer. Our calculation of quantum capacitance confirms the advantage of Al substituting S atom in single-vacancy VS MoS2 systems, and it is suitable for symmetric supercapacitors. We also find that B substituting S atom in pristine MoS2 monolayer has a high quantum capacitance, and it is available as potential electrode materials for asymmetric supercapacitors. We demonstrate that the increase of quantum capacitance is due to the formation of local states near Fermi level and/or the shift of Fermi level caused by defects and doping.