MnO2 nanospheres integrated into hierarchical porous carbon as electrode for high performance asymmetrical supercapacitors

Abstract

Hierarchical porous carbon (HPC) is considered as an ideal electrode material for supercapacitors on account of its high stability and developed pore structure. MnO2, possessing ultrahigh theoretical capacitance, can provides pseudocapacitance to facilitate electrochemical performances. Herein, HPC with large specific surface area (1153 m2 g−1) and abundant mesopores (95.76 % mesopore ratio) is prepared via ZnCl2 activation, which can act as the support and substrate for MnO2. Subsequently, in-situ synthesis of MnO2 nanospheres and preparation of MnO2/HPC composites (MnO2@HPCs) are realized simultaneously by a simple redox reaction. Benefiting from high conductivity of HPC (4.07 S m−1) and moderate size of MnO2 nanospheres (∼40–50 nm), MnO2@HPCs exhibit an excellent specific capacitance (521 F g−1 at 0.5 A g−1 and 468 F g−1 at 1 mV s−1) and pseudocapacitance effect in three-electrode system. Further, the asymmetric supercapacitor adopting MnO2@HPC160 and HPC as the cathode and anode delivers a superior capacitance value (74 F g−1 at 0.5 A g−1), outstanding rate performance (79.7 % at 10 A g−1) and remarkable energy density of 32.93 Wh kg−1 in 1 M Li2SO4 electrolyte. These results demonstrate that the MnO2/hierarchical porous carbon composite is a promising candidate as electrode material for high-performance supercapacitors.