Computational Studies on the Electrochemical Performance of Doped and Substituted Ti3C2Tx (T = O,OH) MXene

Using Density functional theory (DFT) in conjunction with a solvation model, we have investigated the phenomenon of electrode-electrolyte interaction at the electrode surface and its consequences on the electrochemical properties like the charge storage and total capacitance of doped and substituted functionalized Ti 3 C 2 T x (T = O, OH) supercapacitor electrode. We have studied nitrogen-doped, nitrogen substituted, and molybdenum substituted MXenes in acidic electrolyte H 2 SO 4 solution. By considering nitrogen doping at different sites, we found that the greatest capacitance is obtained for doping at functional sites. Our results agree well with the available experiment. We also found that the enhancement in capacitances due to nitrogen doping is due to amplifications in the pseudocapacitance. We propose that the primary mechanism leading to the enhanced value of the capacitances due to nitrogen doping is surface redox activity. The performances of substituted systems, on the other hand, are degraded compared to the pristine ones. This suggests that better storage capacities in Ti 3 C 2 T x electrode can be obtained by doping only. We provide insights into the reasons behind contrasting behavior in doped and substituted systems and suggest ways to further improve the capacitances in the doped system.