Self-template route to MnO2 hollow structures for supercapacitors

Birnessite-type MnO2 hierarchical hollow structures were prepared through a self-template route, by the direct reaction between the aqueous solution of KMnO4, and solid MnCO3 precursor crystals, and followed by the removal of MnCO3 core with HCl. Field emission scanning microscopy (FESEM) images indicate that the shells of hierarchical hollow structures consist of the interconnected sheets with a thickness of about 30 nm, and transmission electron microscopy (TEM) images show that the thickness of the shells can be adjusted over a range from 50 to 80 nm by changing the molar ratio of MnCO3/KMnO4 The electrochemical properties of the as-prepared MnO2 were characterized by cyclic voltammetry (CV) and galvanostatic charge-discharge tests in 1 M Na2SO4 solution The sample obtained at a higher MnCO3/KMnO4 molar ratio (i e 50 1) shows a relatively higher specific capacitance of 169 F g(-1) than 111 F g(-1) of the sample obtained under a lower molar ratio of 25.1 at the current density of 250 mA g(-1) (C) 2010 Elsevier B V. All rights reserved