Hierarchical Mn₂O₃ Microspheres In-Situ Coated with Carbon for Supercapacitors with Highly Enhanced Performances

Porous Mn₂O₃ microspheres have been synthesized and in-situ coated with amorphous carbon to form hierarchical C@Mn₂O₃ microspheres by first producing MnCO₃ microspheres in solvothermal reactions, and then annealing at 500 °C. The self-assembly growth of MnCO₃ microspheres can generate hollow structures inside each of the particles, which can act as micro-reservoirs to store biomass-glycerol for generating amorphous carbon onto the surfaces of Mn₂O₃ nanorods consisting of microspheres. The C@Mn₂O₃ microspheres, prepared at 500 °C, exhibit highly enhanced pseudocapacitive performances when compared to the particles after annealed at 400 °C and 600 °C. Specifically, the C@Mn₂O₃ microspheres prepared at 500 °C show high specific capacitances of 383.87 F g^-1 at current density of 0.5 A g^-1, and excellent cycling stability of 90.47% of its initial value after cycling for 5000 times. The asymmetric supercapacitors assembled with C@Mn₂O₃ microspheres after annealed at 500 °C and activated carbon (AC) show an energy density of up to 77.8 Wh kg^-1 at power density of 500.00 W kg^-1, and a maximum power density of 20.14 kW kg^-1 at energy density of 46.8 Wh kg^-1. We can attribute the enhanced electrochemical performances of the materials to their three-dimensional (3D) hierarchical structure in-situ coated with carbon.