Tunable supercapacitance of electrospun Mn3O4 beaded chains via charge- discharge cycling and control parameters

Abstract

Here we report on the tunable supercapacitance of the Mn3O4 beaded chains synthesized by a simple and low cost electro-spinning process. Tuning is achieved by controlled phase transformation of surface spinel Mn3O4 beaded chains to layered-birnessite MnO2 nanoflakes through galvanostatic charge-discharge cycling. Phase transformation rate is optimized to get maximum capacitance by controlling the parameters such as applied specific current value, number of galvanostatic charge-discharge cycles, micro-structure of working electrode material and the selection of potential range. A maximum specific capacitance of ∼445Fg−1 and areal capacitance of ∼495mFcm−2 are obtained at current densities of 0.5Ag−1 and 0.125mAcm−2 respectively. The superior performance in case of layered-spinel composites among similar nanostructures is due to high surface to volume ratio of the MnO2 nanoflakes formed from the Mn3O4 beaded chains which in turn give rise to large number of surface active sites for the redox reaction to take place. About 100% of capacity retention and coulombic efficiency are observed for ∼1000 cycles even at a higher current density of 7Ag−1. Morphological dependence of the phase transformation rate is investigated by preparing two different morphologies of Mn3O4viz., octahedrons and spherical nanoparticles.