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

Abstract

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 δ-MnO₂ with a carbon-assisted reaction on the nanographene/MECN was strongly adhered to the substrate. The additional α-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 cm² samples and retaining over 83% after 20 000 cycles in 1 M Na₂SO₄. The MnO₂–MnO₂/nanographene/MECN||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.