Rapid sonochemical synthesis of mesoporous MnO2 for supercapacitor applications

Mesoporous MnO2 samples with average pore-size in the range of 2–20 nm are synthesized in sonochemical method from KMnO4 by using a tri-block copolymer, namely, poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) (P123) as a soft template as well as a reducing agent. The MnO2 samples are found to be poorly crystalline. On increasing the amplitude of sonication, a change in the morphology of MnO2 from nanoparticles to nanorods and also change in porosity are observed. A high BET surface area of 245 m2 g−1 is achieved for MnO2 sample. The MnO2 samples are subjected to electrochemical capacitance studies by cyclic voltammetry (CV) and galvanostatic charge–discharge cycling in 0.1 M aqueous Ca(NO3)2 electrolyte. A maximum specific capacitance (SC) of 265 F g−1 is obtained for the MnO2 sample synthesized in sonochemical method using an amplitude of 30 μm. The MnO2 samples also possess good electrochemical stability due to their favourable porous structure and high surface area.