MXenes have the excellent electrochemical properties as electrode of supercapacitors. Using density functional theory, we investigated the electronic properties and quantum capacitance of Zr2CO2 with atomic swap. The atomic swap results in the appearance of Frenkel‐type defect and Schottky defect. The negative binding energy confirms the stability of the studied systems. The atomic swap makes ZrC1, ZrC2, ZrO1, ZrO2, CO2 systems maintain the indirect semiconductor character, and CO2 system has the direct semiconductor character. The thermionic emission performance of Zr2CO2 MXene is greatly improved by atomic swap. ZrO1 and ZrO2 systems in aqueous system are appropriate anode materials. The wide voltage has little effect on the electrode type for perfect Zr2CO2, ZrO1, ZrO2, CO1, and CO2 systems, but changes ZrC1 and ZrC2 systems from cathode material in aqueous system to anode material in ionic/organic system. The work function and effective mass are also explored.

The modulation of electronic properties and quantum capacitance of Sc 2 CF 2 under a perpendicular external E-field was investigated using density functional calculations for the potential application of nanoelectronics and nanophotonics. Sc 2 CF 2 has an indirect band gap of 0.959 eV without an E-field. Furthermore, it undergoes a semiconductingmetallic transition under a positive E-field and a semiconductor−insulator transition under a negative E-field. The application of the negative E-field makes Sc 2 CF 2 have an indirect band gap. Sc-d, F-p, and C-p states are mainly responsible for the significant variation of the band gap. Sc 2 CF 2 under an external E-field always keeps the character of a cathode material under the whole potential. Especially, Sc 2 CF 2 under a negative external E-field is more suitable for the cathode material due to its much smaller |Q p |/|Q n | with much higher Q n . The charge analysis is further performed.