Electronic structures, optical properties and quantum capacitance of 2D Janus ZrMCO2 (M = Sc, Ti, V, Cr, Mn, Fe, Y, Zr, Nb, Mo, Hf, Ta, W) MXenes for supercapacitor electrodes

Double traditional metal (TM) Janus MXenes have more superior properties when compared with MXenes. The electronic and optical properties, Bader charge and quantum capacitance of ZrMCO2 (M = Sc, Ti, V, Cr, Mn, Fe, Y, Zr, Nb, Mo, Hf, Ta, W) are explored by density functional theory (DFT). The stability of these systems is confirmed by cohesive energy. The substitution of Ti/Hf atoms results in the decrease of bandgap of ZrTiCO2/ZrHfCO2, which is induced by the redshift of conduction band minimum (CBM). ZrMCO2 (M = Cr, Mn) are magnetic semiconductors and ZrMCO2 (M = Sc, V, Y, Fe) are magnetic metals. All doping atoms except Hf improve the maximum quantum capacitance of ZrMCO2 at positive bias. Wide voltage makes ZrMCO2 (M = Nb, Ta, W) change into anode material and ZrFeCO2 into cathode material. ZrMCO2 (M = Sc, Mn, Y, Hf, Zr) and ZrMCO2 (M = V, Cr) can serve as cathode and anode materials in whole voltage, respectively. Much charge accumulating between Fe and C atoms results in the smallest Fe–C bond among all M − C bonds, which indicates the strongest interaction between Fe and C atoms. Optical properties and work function are further explored.