Intrinsic Charge Storage Capability of Transition Metal Dichalcogenides as Pseudocapacitor Electrodes

The intrinsic charge storage capability of a series of transition metal dichalcogenides (TMDs) (MS2, M = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Zr, Nb, Mo, Tc, Hf, Ta, W, Re, and MoX2, X = S, Se, Te) is investigated using density functional theory calculations. A map for pseudocapacitor electrodes is provided, depending on the demands of high conductivity and a remarkable peak of density of states (DOS) in the range of the electrolyte window. The calculated DOS suggests that most of the T phase structures are superior to H phase in electroconductibility. The charge storage capability is represented by the number of gaining or losing electrons calculated by integrating DOS in the electrolyte window. MS2 (M = Ti, V, Cr, Fe, Nb, Mo, Tc) of the T phase is conductive and gains electrons easily with considerable valence state change of the TM atom, showing a redox pseudocapacitance character as a cathode. Meanwhile, CoS2-H and MoSe2-T are promising anode materials. Moreover, the chalcogen (S, Se, Te) with different electronegativity and work function will result in the changes of Fermi level and surface polarization of MoX, leading to the shift of their DOS in the electrolyte window. In another way, the metallic hydrogenated H phase of MoS2 (MoS2H2) with conductivity should have enhanced advanced electrochemical performance.