Facile in-situ redox synthesis of hierarchical porous activated carbon@MnO2 core/shell nanocomposite for supercapacitors

In this paper, hierarchical porous activated carbon@manganese dioxide (AC@MnO2) core-shell nanocomposite for supercapacitors have been synthesized by a facile in-situ chemical redox reaction. The microstructures of as-prepared materials have been characterized by Fourier transform-infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and nitrogen sorption isotherm measurements. Electrochemical properties of as-prepared samples were studied by cyclic voltammetry (CV), galvanostatic charging–discharging (GCD) and electrochemical impedance spectroscopy (EIS) tests in 6 mol L−1 KOH aqueous electrolytes based on their two-electrode symmetric capacitors. Thanks to the advanced hierarchical porous core/shell nanostructures, the AC@MnO2 composite exhibit a larger specific surface area (658.1 m2 g−1) compared with either AC (557.9 m2 g−1) or MnO2 (113.6 m2 g−1) and show a lower charge transfer resistance (0.74 Ω) and Warburg resistance (0.16 S sec0.5) than those of AC (0.96 Ω, 0.11 S sec0.5) and MnO2 (0.82 Ω, 0.054 S sec0.5), which all contribute to the improved electron/ion transport processes and the superior capacitive performance. The results show that AC@MnO2 composite exhibit enhanced specific capacitance (193 F g−1, 0.2 A g−1), rate performance (154 F g−1, 2 A g−1) and cycling stability (77.8% retention after 1500 cycles at 0.8 A g−1) than those of AC (181 F g−1, 0.2 A g−1; 129 F g−1, 2 A g−1; 50% retention after 1500 cycles) and MnO2 (64 F g−1, 0.2 A g−1; 10 F g−1, 2 A g−1; 11.3% retention after 1500 cycles). The superior capacitive behavior and the facile preparation method indicate a good candidate of the hierarchical porous AC@MnO2 core/shell nanocomposite for supercapacitors.