Quantum capacitance of supercapacitor electrodes based on the F-functionalized M2C MXenes: A first-principles study

MXenes are widely applied in electrodes of supercapacitors because of the higher volume/surface ratio. In this paper, density functional theory (DFT) is used to investigate the quantum capacitance (Cdiff) and surface storage charge (Q) of F-functionalized M2C (M = Sc, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, W) MXenes in aqueous and ionic/organic systems. Three possible configurations for F termination are explored, and M-top configuration with F on top of M atom is the most stable. The results indicate that Sc2CF2 is the most suitable cathode material of asymmetric supercapacitor in aqueous and ionic/organic systems, while V2CF2 is the most preferred anode material of asymmetric supercapacitor. Ti2CF2 and Zr2CF2 are electrode materials of symmetric supercapacitor in aqueous and ionic/organic systems. The extension of the voltage modulates Mo2CF2 from the electrode material of symmetric capacitance in aqueous system to the most suitable anode material in ionic/organic system. Nb2CF2 and Ta2CF2 are potential cathode materials in aqueous system, but change to the suitable anode materials in ionic/organic system. Our findings provide the theoretical foundation to develop MXene-based supercapacitors and energy-storage devices.