Three-dimensional (3D) spinel-type MnO 2 has attracted extensive interest as a potential electrode material for supercapacitors in order to meet cost/performance requirements of power supplies. In this study, MnO 2 microspheres (MS-MnO 2 ) with a 3D spinel phase and 0.5−4.0 μm size were constructed from small MnO 2 nanoparticles by a rapid and facile solvothermal process in which tetraethylammonium (TEA) was used as the template. The properties of the synthesized spinel MS-MnO 2 for use in supercapacitors were investigated by cyclic voltammetry and galvanostatic charge/discharge measurements using a three-electrode system in a neutral 1 M Na 2 SO 4 electrolyte. The synthesized spinel MS-MnO 2 exhibited faster charge/discharge rates and higher capacitance than commercial MnO 2 materials. The obtained results showed that the as-prepared spinel MS-MnO 2 possessed good specific capacitance (SC) of ∼190 F/g at 0.5 A/g. The spinel MS-MnO 2 also exhibited excellent SC retention and Coulombic efficiency of ∼100% and ∼95%, respectively, after 1000 cycles at 1 A/g, suggesting its potential application in supercapacitors. In addition, manganese oxides with large cavities were obtained through postannealing treatment and showed their potential for use in energy-storage devices, energy-conversion systems, catalysts, and sensors.

We present a simple and quick procedure for the one-pot synthesis of manganese oxides under a basic solvothermal condition in the presence of cationic surfactants acting as the template in a 2-butanol/water solution. Three-dimensional spinel-type MnO 2 microspheres composed of small nanoparticles have been fabricated for the first time using our method. Their corresponding electrochemical performances in the applications of supercapacitor electrodes exhibit a good specific capacitance (SC) value of ;190 F/g at 0.5 A/g and excellent SC retention and Coulombic efficiency of ;100% and ;95% after 1000 charge/discharge cycles at 1 A/g, respectively. This suggests its potential applications in energy storage devices. Further, we demonstrate that this solvothermal technique enables the morphological tuning of manganese oxides in various forms such as schists, rods, fibers, and nanoparticles. This work describes a rapid and low-cost technique to fabricate novel architectures of manganese oxides having the desired crystal phase, which will highly benefit various supercapacitor applications.

With an aim to develop environment friendly and inexpensive materials for electrochemical capacitor electrodes, nanocrystalline gamma-MnO2 with layered architecture of schist-like structure was successfully synthesized by reducing mixed MnSO4 center dot H2O and CTAMnO(4) precursors in stoichiometric amounts through a hydrothermal process. The as-prepared MnO2 was characterized by field emission scanning electron microscopy, X-ray diffraction, and thermal gravimetric analysis. Also, cyclic voltammetry was employed to investigate the electrochemical properties of the products in neutral KCl aqueous solution, showing a higher enhanced capacitive performance than that of the sample without a coating of schist-like gamma-MnO2, indicating that our MnO2-based electrode provides a promising opportunity for high-performance energy storage devices