(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 Ti₃C₂T_x (T = O, OH) supercapacitor electrode. We have studied nitrogen-doped,

nitrogen substituted, and molybdenum substituted MXenes in acidic electrolyte H₂SO₄ 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 Ti₃C₂T_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.