Designing high performance MXene supercapacitors through functionalization and defect engineering: A theoretical study

Abstract

Supercapacitors (SCs) have attracted significant attention as energy storage devices due to their large power efficiency, excellent stability, prolonged cycle life and short recharge time. Ti-based MXenes have attracted considerable attention as promising candidates for SC electrodes due to their extraordinary physicochemical properties, such as high charge storage capacity, excellent electrical conductivity, unique layered structure, and the presence of multiple surface functional groups. In this study, Ti2CX2 (X = Cl, F, Br, O, P, S, Se, Si and Te) MXene, both with and without carbon vacancies, were investigated as SC electrode materials using DFT. The structural stability, dynamic stability, density of states, quantum capacitance, average quantum capacitance, surface charge density, work function, integrated charge density, isosurface charge density difference, and bader charge analysis of all MXenes are studied. Results revealed that CQ and Q significantly changed due to varying the functional group, and introduction of carbon vacancy significantly enhanced the CQ and Q. For the aqueous system, all MXene exhibited asymmetrical behavior except Ti2CF2 + VC and Ti2CP2 + VCMXenes. The calculated results illustrate that Ti2CTe2 + VC (478 & micro;C & sdot;cm-2) and Ti2CSi2 + VC (-750.7 & micro;C & sdot;cm-2) MXenes are the best anode and cathode respectively. In the case of an ionic/organic system, all MXenes exhibited asymmetrical behavior. The calculated findings show that Ti2CTe2 (1136.9 & micro;C & sdot;cm-2) and Ti2CSi2 + VC (-930.7 & micro;C & sdot;cm-2) MXenes are the best anode and cathode respectively. The work function of Ti2CTe2, Ti2CTe2 + VC and Ti2CSi2 + VCMXenes is lower than that of the other investigated MXenes, indicating that power efficiency of these MXenes based SCs is high. The findings reveal that Ti2CTe2, Ti2CTe2 + VC and Ti2CSi2 + VCMXenes give better results as compared to previously reported Ti-based MXenes, positioning them as strong candidates for next-generation SC electrodes.