MnO2 nano/micro hybrids for supercapacitors: “Nano's Envy, Micro's pride”

Abstract

The present study provides the first reports on a low temperature molten salt route which can generate unique architecture of MnO₂ nanospikes arrayed in a peculiar fashion to form micron sized ball morphology. This morphology when employed as supercapacitor electrodes gives an advantage of surface relaxation during the charge–discharge process making it super stable. The study highlights the advantages of nanostructuring of microparticles which can answer the toxicity issues and their potential as a commercial product. This claim in the present study has been validated by cell toxicity study on human dermal fibroblasts, which established that a nano/micro hybrid structure can be relatively less toxic. Cytoskeleton rearrangements were also observed as the size of MnO₂ was reduced from micron to nanoscale. A mechanism of the structure formation and the influence of the salt in controlling the process parameters as well as the morphology are also proposed. These electrodes in coin cells exhibited specific mass capacitance value as high as 1100 F g⁻¹ with a power density and energy density of 4.5 W h kg⁻¹ and 14 kW kg⁻¹, respectively.