@article{MakgopaEjikemeJaftaetal.2015,
  author    = {Katlego Makgopa and Paul M. Ejikeme and Charl J. Jafta and Kumar Raju and Marco Zeiger and Volker Presser and Kenneth I. Ozoemena},
  title     = {A high-rate aqueous symmetric pseudocapacitor based on highly graphitized onion-like carbon/birnessite-type manganese oxide nanohybrids},
  series   = {Journal of Materials Chemistry A},
  volume    = {3},
  number    = {7},
  issn      = {2050-7488},
  doi       = {10.1039/c4ta06715k},
  url       = {https://nbn-resolving.org/urn:nbn:de:bsz:291:415-3994},
  pages     = {3480 -- 3490},
  year      = {2015},
  abstract  = {We present a study on the pseudocapacitive properties of birnessite-type MnO 2 grafted on highly graphitized onion-like carbon (OLC/MnO 2 ). In a three-electrode setup, we evaluated two different substrates, namely a platinum disc and nickel foam. The OLC/MnO 2 nanohybrid exhibited a large specific capacitance (C sp ) of 295 and 323 F g -1 (at 1 A g -1 ) for the Pt disc and Ni foam, respectively. In addition, the Ni foam substrate exhibited much higher rate capability (power density) than the Pt disc. A symmetrical two-electrode device, fabricated with the Ni foam, showed a large C sp of 254 F g -1 , a specific energy density of 5.6 W h kg -1 , and a high power density of 74.8 kW kg -1 . These values have been the highest for onion-based electrodes so far. The device showed excellent capacity retention when subjected to voltage-holding (floating) experiments for 50 h. In addition, the device showed a very short time constant ([small tau] = 40 ms). This high rate handling ability of the OLC/MnO 2 nanohybrid, compared to literature reports, promises new opportunities for the development of aqueous-based pseudocapacitors.},
  language  = {en}
}