In-situ growth of MnO2 crystals under nanopore-constraint in carbon nanofibers and their electrochemical performance

Growing MnO 2 nanocrystals in the bulk of porous carbon nanofibers is conducted in a KMnO 4 aqueous solution aimed to enhance the electrochemical performance of MnO 2 . The rate of redox reaction between KMnO 4 and carbon was controlled by the concentration of KMnO 4 in a neutral solution. The MnO 2 nanoparticles grow along with (211) crystal faces when the redox reaction happens on the surface of fibers under 1D constraint, while the nanoparticles grow along with (200) crystal faces when the redox reaction happens in the bulk of fibers under 3D constraint. The composite, where MnO 2 nanoparticles are formed in the bulk under a constraint, yields an electrode material for supercapacitors showing good electron transport, rapid ion penetration, fast and reversible Faradaic reaction, and excellent rate performance. The capacitance of the composite electrode could be 1282 F g −1 under a current density of 0.2 A g −1 in 1 M Na 2 SO 4 electrolyte. A symmetric supercapacitor delivers energy density of 36 Wh kg −1 with power density of 39 W kg −1 , and can maintain 7.5 Wh kg −1 at 10.3 kW kg −1 . It exhibits an excellent electrochemical cycling stability with 101% initial capacitance and 95% columbic efficiency even after 1000 cycles of charge/discharge.