$\alpha -$MnO$_{2}$ Nanorod-composites as Electrode Material for Supercapacitors

MnO$_{2}$-based supercapacitors as electrochemical storage systems have attracted immense interest due to their low cost, natural abundance, high theoretical specific capacitance and environmental friendliness. We have synthesized $\alpha $-MnO$_{2}$ and $\alpha $-MnO$_{2}$/CNF (carbon nanofibers, 5 wt{\%}) nanocomposites using co-precipitation method. The XRD results confirm the formation of a single phase $\alpha $-MnO$_{2}$ and SEM, TEM studies reveal the formation of nanorods of $\alpha $-MnO$_{2,\, }$but with a larger size in the case of $\alpha $-MnO$_{2}$-CNF nanocomposites. Pure $\alpha $-MnO$_{2}$ shows a larger surface area (266 m$^2$ /g), and lower electrical conductivity (0.02 S/cm) compared to that of $\alpha $-MnO$_{2}$-CNF (131 m$^2$ /g, 0.67 S/cm). Cyclic voltammetry (CV) studies and galvanostatic charge/discharge studies have been performed on $\alpha $-MnO$_{2\, }$nanocomposites, coated on Ni foam, using a potential ranging from -0.02 to 0.8 V, in a 1 M Na$_{2}$SO$_{4}$ aqueous solution. The measured specific capacitance of $\alpha $-MnO$_{2}$ is 245 F/g whereas that of $\alpha $-MnO$_{2}$-CNF is 192 F/g. Although, the electrical conductivity of $\alpha $-MnO$_{2}$-CNF is higher than that of $\alpha $-MnO$_{2}$, its observed lower specific capacitance is attributed to its reduced surface area compared to $\alpha $-MnO$_{2}$. Currently, we are optimizing the amount of CNF in $\alpha $-MnO$_{2}$-CNF nanocomposites to enhance supercapacitor performance.