Ultra fine MnO2 nanowire based high performance thin film rechargeable electrodes: Effect of surface morphology, electrolytes and concentrations

The present study demonstrates a novel approach by which titanium foils coated with MnO2 nanowires can be processed into a high surface area electrode for rechargeable energy storage applications. A detailed study has been performed to elucidate how surface morphology and redox reaction behaviors underlying these electrodes impact the cyclic and capacitive behavior of the electrode. These nanowires were synthesized hydrothermally and exhibited an aspect ratio in the order of 10(2). BET analysis revealed that these MnO2 nanowires show a high surface area of 44 m(2) g(-1). From the analysis of the relevant electrochemical parameters, an intrinsic correlation between the capacitance, internal resistance and the surface morphology has been deduced and explained on the basis of relative contributions from the faradic properties of the MnO2 in different electrolytes. Depending on the type of surface morphology incorporated, these thin film nanowire electrodes exhibited specific mass capacitance value as high as 1050 F g(-1) and 750 F g(-1) measured from cyclic voltammetry and charge-discharge curves respectively. It has been shown that electrodes based on such nanowires can allow significant room for improvement in the cyclic stability of a hybrid supercapacitor/battery system. Further, a working model supercapacitor in cylindrical form is also shown exhibiting a capacitance of 10 F.