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

A two-step hydrothermal process is designed to synthesize hybrid MnO 2 /C nano-composites on a macroporous electrically conductive network (MECN) via a redox reaction in a 30 mM KMnO 4 solution with carbon microspheres. The microstructure, surface morphology, and electrochemical properties of the MnO 2 /C coated on MECN are determined systematically. The MnO 2 nanoflakes, which are about 40-200 nm, are deposited regularly on the carbon microspheres coated on the MECN electrode. The MnO 2 nano-lamellas offer fast ion transport and adsorption-desorption to/from the MnO 2 surface, and the microporous carbon microspheres enhance the electrical storage and ion transfer. The in situ growth of MnO 2 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 Na 2 SO 4 . The MnO 2 /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. Hybrid MnO 2 /C nano-composites are formed on a macroporous electrically conductive network as a negative electrode. Three devices packaged in CR2032 batteries in series can power a blue LED for about 100 minutes after charging each hybrid device for 30 s.