Effect of surface functionalization on the quantum capacitance of M2CF2 (M = Ti, V, Cr, Zr, Nb, Mo) as supercapacitor electrodes

The surface charge storage capacity, atomic structures, and quantum capacitance of M2CF2 (M=Ti, V, Cr, Zr, Nb, Mo) are investigated using density functional theory (DFT). The influence of different surface functionalization methods on the capacitance performance of M2CF2 is also examined, including the introduction of vacancy defects (C-, F-, M-vacancy) and nonmetal doping (N, O, and S). The findings show that both defects and doping reduce the quantum capacitance of V2CF2, Cr2CF2, and Mo2CF2, but they have a negligible impact on the capacitance behavior of Ti2CF2, Zr2CF2 and Nb2CF2. Furthermore, the pristine Cr2CF2 system exhibits relatively high quantum capacitance and surface charge storage capacity under both positive and negative bias. However, the presence of vacancies and dopants significantly decreases its capacitance. Among the structures studied, pristine and nonmetal-doped V2CF2 demonstrate the highest quantum capacitance values (1302.02-1517.56 mu F/ cm2), suggesting its potential as an effective positive electrode material. Overall, the findings of this study are expected to boost the development of high-capacitance electrodes in the future.