Mesoporous MnO ₂ synthesized by hydrothermal route for electrochemical supercapacitor studies

Poorly crystalline mesoporous MnO ₂, which is suitable for supercapacitor studies, is synthesized from neutral KMnO ₄ aqueous solution by hydrothermal route. But it requires a high temperature (180 °C) and also a long reaction time (24 h). Addition of a tri-block copolymer, namely, poly(ethylene glycol)-block-poly(propylene glycol)-blockpoly( ethylene glycol) (P123), which is generally used as a soft template for the synthesis of nano-structured porous materials, reduces the hydrothermal temperature to 140 °C and also reaction time to 2 h. When the reaction time is increased, the product morphology changes from nanoparticles to nanorods with a concomitant decrease in BET surface area. Also, the product tends to attain crystallinity. The electrochemical capacitance properties of MnO ₂ synthesized under varied hydrothermal conditions are studied in 0.1M Na ₂SO ₄ electrolyte. A specific capacitance of 193 Fg ^-1 is obtained for the mesoporous MnO ₂ sample consisting of nanoparticle and nanorod mixed morphology synthesized in 6 h using P123 at 140 °C.