Three-dimensional homo-nanostructured MnO2/nanographene membranes on a macroporous electrically conductive network for high performance supercapacitors

A three-step hydrothermal route was designed to fabricate three-dimensional (3D) homo-nanostructured MnO2 (MnO2-MnO2)/nanographene membranes on a macroporous and electrically conductive network (MECN). The preparation technology, structure and morphology, and electrochemical properties of samples are determined systematically. The nanographene/MECN electrode with more defects as the active surface had been synthesized by hydrothermal carbonization. The in situ growth of delta-MnO2 with a carbon-assisted reaction on the nanographene/MECN was strongly adhered to the substrate. The additional alpha-MnO2 with a redox reaction enhanced the mass loading of MnO2, developing the specific capacitance of the MnO2-MnO2/nanographene/MECN electrode. The materials are demonstrated as an electrode with a maximum capacitance of 4.5 F cm(-2) or 179 F cm(-3) (894 F g(-1)) at 1 mA cm(-2) for 1 cm(2) samples and retaining over 83% after 20 000 cycles in 1 M Na2SO4. The MnO2-MnO2/nanographene/ MECN parallel to AC/Ni-foam supercapacitors with high volumetric energy densities exhibit the ideal performance of a supercapacitor (1 mW h cm(-3), 40.3 W h kg(-1), at 1000 W kg(-1)), indicating a promising future for supercapacitors.