Browsing by Author "Lekitima, J. N. et al"

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    High-performance symmetric electrochemical capacitor based on graphene foam and nanostructured manganese oxide
    (AIP Publishing, 2013) Bello, A.; Fashedemi, O. O.; Lekitima, J. N. et al
    We have fabricated a symmetric electrochemical capacitor with high energy and power densities based on a composite of graphene foam (GF) with ?80 wt% of manganese oxide (MnO2) deposited by hydrothermal synthesis. Raman spectroscopy and X-ray diffraction measurements showed the presence of nanocrystalline MnO2 on the GF, while scanning and transmission electron microscopies showed needle-like manganese oxide coated and anchored onto the surface of graphene. Electrochemical measurements of the composite electrode gave a specific capacitance of 240 Fg?1 at a current density of 0.1 Ag?1 for symmetric supercapacitors using a two-electrode configuration. A maximum energy density of 8.3 Whkg?1 was obtained, with power density of 20 kWkg?1 and no capacitance loss after 1000 cycles. GF is an excellent support for pseudo-capacitive oxide materials such as MnO2, and the composite electrode provided a high energy density due to a combination of double-layer and redox capacitance mechanisms.
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    Microwave assisted synthesis of MnO2 on nickel foam-graphene for electrochemical capacitor
    (Elsevier, 2013) Bello, A.; Fashedemi, O. O.; Lekitima, J. N. et al
    A green chemistry approach (hydrothermal microwave irradiation) has been used to deposit manganese oxide on nickel foam-graphene. The 3D graphene was synthesized using nickel foam template by chemical vapor deposition (CVD) technique. Raman spectroscopy, X-ray diffraction (XRD), scanning electron and transmission electron microscopies (SEM and TEM) have been used to characterize structure and surface morphology of the composite, respectively. The Raman spectroscopy measurements on the samples reveal that 3D graphene consists of mostly few layers with low defect density. The composite was tested in a three electrode configuration for electrochemical capacitor, and exhibited a specific capacitance of 305 F g?1 at a current density of 1Ag?1 and showed excellent cycling stability. The obtained results demonstrate that microwave irradiation technique could be a promising approach to synthesis graphene based functional materials for electrochemical applications.