  Surface Engineering in two-dimensional(2D) materials has turned out to be an
useful technique to improve their functional properties. By designing Janus
compounds MM$^{\prime}$C in MXene family of compounds M$_{2}$C where the two
surfaces are constituted by two different transition metal M and M$^{\prime}$,
we have explored their potentials as electrodes in a supercapacitor with acidic
electrolyte. Using Density functional Theory (DFT) \cite{dft} in conjunction
with classical solvation model we have made an in depth analysis of the
electrochemical parameters of three Janus MXenes, passivated by oxygen - NbVC,
MnVC and CrMnC. Comparisons with the corresponding end point MXenes Nb$_{2}$C,
V$_{2}$C, Mn$_{2}$C and Cr$_{2}$C are also made. We find that the surface redox
activity enhances due to formation of Janus, improving the charge storage
capacities of MXene electrodes significantly. Our analysis reveals that the
improved functionality has its root in the variations in the charge state of
one of the constituents in the Janus compound which, in turn, has its origin in
the electronic structure changes due to the surface manipulation. Our work,
which is the first on the electrochemical properties of Janus MXenes for
supercapacitor applications, suggests the surface engineering by forming
appropriate Janus compounds as a possible route to extract high power density
in a MXene electrode-acidic electrolyte based energy storage devices.
