Synthesis of MnO2/N-doped ultramicroporous carbon nanospheres for high-performance supercapacitor electrodes

We demonstrate a simple and highly efficient strategy to synthesize MnO₂/nitrogen-doped ultramicroporous carbon nanospheres (MnO₂/N-UCNs) for supercapacitor application. MnO₂/N-UCNs were fabricated via a template-free polymerization of resorcinol/formaldehyde on the surface of phloroglucinol/terephthalaldehyde colloids in the presence of hexamethylenetetramine, followed by carbonization and then a redox reaction between carbons and KMnO₄. As-prepared MnO₂/N-UCNs exhibits regular ultramicropores, high surface area, nitrogen heteroatom, and high content of MnO₂. A typical MnO₂/N-UCNs with 57 wt.% MnO₂ doping content (denoted as MnO₂(57%)/N-UCNs) makes the most use of the synergistic effect between carbons and metal oxides. MnO₂(57%)/N-UCNs as a supercapacitor electrode exhibits excellent electrochemical performance such as a high specific capacitance (401 F/g at 1.0 A/g) and excellent charge/discharge stability (86.3% of the initial capacitance after 10,000 cycles at 2.0 A/g) in 1.0 mol/L Na₂SO₄ electrolyte. The well-designed and high-performance MnO₂/N-UCNs highlight the great potential for advanced supercapacitor applications.