Hybrid MnO2/C nano-composites on a macroporous electrically conductive network for supercapacitor electrodes

A two-step hydrothermal process is designed to synthesize hybrid MnO2/C nano-composites on a macroporous electrically conductive network (MECN) via a redox reaction in a 30 mM KMnO4 solution with carbon microspheres. The microstructure, surface morphology, and electrochemical properties of the MnO2/C coated on MECN are determined systematically. The MnO2 nanoflakes, which are about 40-200 nm, are deposited regularly on the carbon microspheres coated on the MECN electrode. The MnO2 nano-lamellas offer fast ion transport and adsorption-desorption to/from the MnO2 surface, and the microporous carbon microspheres enhance the electrical storage and ion transfer. The in situ growth of MnO2 on the carbon microspheres on the MECN substrate leads to a small contact resistance and short current transfer length. The materials are demonstrated to be excellent electrodes in supercapacitors boasting a high capacitance of 497 F g(-1) at 1 A g(-1) with a 1 cm(2) electrode and excellent long-term cycling stability over 5000 cycles in 1 M Na2SO4. The MnO2/C/MECN||active carbon/Ni-foam asymmetrical supercapacitors (ASCs) deliver an energy density of 0.50 mW h cm(-3) (55.5 W h kg(-1) at a power density of 4000 W kg(-1)) with 87.6% retention of the specific capacitance after 5000 cycles.