Mesoporous MnO2 synthesized by using a tri-block copolymer for electrochemical supercapacitor studies

Mesoporous MnO2 is prepared from KMnO4 by using a tri-block copolymer, namely, poly(ethylene glycol)–block-poly(propylene glycol)–block-poly(ethylene glycol) (PEG–PPG–PEG) as a reducing as well as a structure-directing agent. The as synthesized MnO2 samples are poorly crystalline with mesoporosity having pore diameter between 8 and 40 nm. BET surface area as high as 273 m2 g−1 is obtained. By heating, the poorly crystalline MnO2 turns into a well crystalline form at 400 °C with nanorod morphology. However, the surface area decreases for the heated samples. Samples of MnO2 prepared by varying the ratio of KMnO4 and the copolymer, and also the heated samples are subjected to electrochemical characterization for supercapacitor studies. High specific capacitance values on mass basis are obtained for the as prepared mesoporous MnO2 samples.

(A) BET isotherm and (B) BJH pore size distribution (inset) of MnO2 (S5.5).Figure optionsDownload as PowerPoint slideHighlights
► Synthesis of mesoporous MnO2 samples with pore diameter 8 - 40 nm.
► BET surface area as high as 273 m2 g-1.
► Change in morphology from nanoparticles to nanorods at temperatures ⩾ 400 °C.
► Specific capacitance of 241 F g-1 in 0.1 M Ca(NO3)2 electrolyte.
► Decrease in surface area and hence specific capacitance on heating.