Facile hydrothermal synthesis of urchin-like cobalt manganese spinel for high-performance supercapacitor applications

A facile hydrothermal method has been adopted to synthesize the spherical urchin-like hierarchical CoMn2O4 nanostructures on the nickel foam substrate. The as-synthesized urchins have an average diameter of ∼3–7 μm with numerous self-assembled nanoneedles grown radically in all the directions from its center with a huge void space between them. For comparison, we have also studied the electrochemical as well as other physicochemical properties of parent simple Co3O4 and MnO2 materials, which were also synthesized by a similar hydrothermal method. The results show that CoMn2O4 electrode displayed significantly higher (more than two times) areal and specific capacitances compared to Co3O4 and MnO2 electrodes with excellent capacitance retention and Coulombic efficiency. Moreover, the energy and power densities obtained for CoMn2O4 electrode are also far higher than the parent Co3O4 and MnO2. Long-term cycling tests of CoMn2O4 electrode shows the improved capacitance with high rate capability up to 6000 cycles indicating their potential for high performance supercapacitor applications. The better electrochemical performance of CoMn2O4 electrode can be attributed to the smart urchin-like nanostructures, which has several advantages like, more electroactive sites for faradic reactions emerging from the two metal ions, higher electronic/ionic conductivity and fast electrolyte transportation kinetics promoted by unique morphology.