Supercapacitors in combination with renewable energy sources can provide environment friendly and sustainable energy devices. But due to their lower energy density, they are not able to replace batteries for all commercial applications. Their energy density can be increased by using high quantum capacitance electrodes. MXenes have potential to be used for such electrodes. In present work, density of states, band structure and quantum capacitance (QC) of bare and functionalized niobium carbide and titanium carbide MXenes are studied using DFT simulations. The calculated quantum capacitances of Nb2C and Ti2C show significant values of 324.1 and 246.2 µF/cm2 respectively. Nb2C shows higher value for QC in comparison to Ti2C for both positive as well as negative electrodes. These calculations are also performed for functionalized MXenes using =O, -F and –OH as functional group. Functionalization of MXenes with these groups reduces the QC of Nb2C and Ti2C MXenes at Fermi level.

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