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

• Published in: Journal of materials chemistry. A, Materials for energy and sustainability Vol. 3; no. 7; pp. 3480 - 3490
• Main Authors: Makgopa, Katlego, Ejikeme, Paul M, Jafta, Charl J, Raju, Kumar, Zeiger, Marco, Presser, Volker, Ozoemena, Kenneth I
• Format: Journal Article
• Language: English
• Published: 01.01.2015
• Subjects: Carbon; Density; Devices; Discs; Disks; Foams; Nanostructure; Nickel; Platinum
• ISSN: 2050-7488; 2050-7496
• DOI: 10.1039/c4ta06715k

We present a study on the pseudocapacitive properties of birnessite-type MnO sub(2) grafted on highly graphitized onion-like carbon (OLC/MnO sub(2)). In a three-electrode setup, we evaluated two different substrates, namely a platinum disc and nickel foam. The OLC/MnO sub(2) nanohybrid exhibited a large specific capacitance (C sub(sp)) of 295 and 323 F g super(-1) (at 1 A g super(-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 sub(sp) of 254 F g super(-1), a specific energy density of 5.6 W h kg super(-1), and a high power density of 74.8 kW kg super(-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 ( tau = 40 ms). This high rate handling ability of the OLC/MnO sub(2) nanohybrid, compared to literature reports, promises new opportunities for the development of aqueous-based pseudocapacitors.