Novel Janus HfMCO2 (M= Cr, Mo, Fe, Nb, Sc, Ta, Ti, V, W, Y and Zr) MXene: Promising candidates for electrode of supercapacitor

Abstract

Janus MXenes have received greater attention for their outstanding properties. The electronic and optical properties, effective mass and quantum capacitance of Janus HfMCO₂ (M = Cr, Mo, Fe, Nb, Sc, Ta, Ti, V, W, Y and Zr) are investigated by using first-principles calculation with HSE06 functional. HfMCO₂ (M = Cr, Fe, V, Y) are magnetic semiconductors. The doping of Mo, Nb, Sc, Ta, and W atoms induces the transition of Hf₂CO₂ from semiconductor to metal. HfCrCO₂, HfScCO₂, and HfVCO₂ have stronger magnetism with magnetic moments. The significant larger m_h∗ of HfFeCO₂ indicates the smaller hole mobility in valence band and slow diffusion. The optical analysis indicates that all the systems except HfVCO₂ have better conductivity than Hf₂CO₂, especially for HfWCO₂ with ε₁(0) of 14.08. The doping of Fe, Ti, Mo, W and Zr atoms drastically increases the absorption coefficient in infrared and visible regions. Janus HfMCO₂ (M = Cr, Fe, Mo, Sc, Ti, V, W and Zr) are suitable for cathode electrode, while HfTaCO₂ and HfYCO₂ are suitable for symmetrical electrode material. Large voltage only changes the electrode types of HfWCO₂ and HfYCO₂ to symmetric and cathode electrodes, respectively. The electrode type of Janus HfMCO₂ having mixed terminations are analyzed.