A high-rate aqueous symmetric pseudocapacitor based on highly graphitized onion-like carbon/birnessite-type manganese oxide nanohybrids

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Authors

Makgopa, Katlego
Ejikeme, Paul Madus
Jafta, Charl Jeremy
Raju, Kumar
Zeiger, Marco
Presser, Volker
Ozoemena, Kenneth I.

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Publisher

Royal Society of Chemistry

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 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 Csp 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 (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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Keywords

Birnessite-type manganese oxide nanohybrids, Onion-like carbon (OLC), Electrical double-layer capacitors (EDLCs), Pseudocapacitors

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Citation

Makgopa, K, Ejikeme, PM, Jafta, CJ, Raju, K, Zeiger, M, Presser, V & Ozoemena, KI 2015, 'A high-rate aqueous symmetric pseudocapacitor based on highly graphitized onion-like carbon/birnessite-type manganese oxide nanohybrids', Journal of Materials Chemistry A, vol. 3, no. 7, pp. 3480-3490.