A high-rate aqueous symmetric pseudocapacitor based on highly graphitized onion-like carbon/ birnessite-type manganese oxide nanohybrids.
Makgopa, Katlego Ejikeme, Paul M. Jafta, Charl J. Raju, Kumar Zeiger, Marco Presser, Volker Ozoemena, Kenneth I
Makgopa, Katlego
Ejikeme, Paul M.
Jafta, Charl J.
Raju, Kumar
Zeiger, Marco
Presser, Volker
Ozoemena, Kenneth I
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Abstract
We present a study on the pseudocapacitive properties of birnessite-type MnO2 grafted on highly graphitized onion-like carbon (OLC/MnO2). In a three-electrode setup, we evaluated two different substrates, namely a platinum disc and nickel foam. The OLC/MnO2 nanohybrid exhibited a large specific capacitance (Csp) of 295 and 323 F g1 (at 1 A g1) 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 Csp of 254 F g1, a specific energy density of 5.6 W h kg1, and a high-power density of 74.8 kW kg1. 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 (s ¼ 40 ms). This high-rate handling ability of the OLC/MnO2 nanohybrid, compared to literature reports, promises new opportunities for the development of aqueous-based pseudocapacitors.
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Date
2014-12-15
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The Royal Society of Chemistry
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Keywords
Pseudocapacitive, Manganese oxide, Nanohybrids, OLC/MnO2, Power density