Abstract
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.
Highlights
IntroductionElectric double-layer capacitors (EDLCs) are charge-storage devices with a high power density, long cyclic life and low maintenance cost. 1-4 They fill the gap between batteries (high energy density) and electrolytic capacitors (high power density). 5, 6 Such properties make them potentially useful for a wide range of applications such as hybrid vehicles, cordless electric tools, memory back-up, cellular phones, medical devices, military and consumer electronics.[7]
Electric double-layer capacitors (EDLCs) are charge-storage devices with a high power density, long cyclic life and low maintenance cost. 1-4 They fill the gap between batteries and electrolytic capacitors. 5, 6 Such properties make them potentially useful for a wide range of applications such as hybrid vehicles, cordless electric tools, memory back-up, cellular phones, medical devices, military and consumer electronics.[7]the energy stored in supercapacitors ( 100 Whkg−1)
We report on a symmetric electrochemical capacitor fabricated using graphene foam (GF)/MnO2 nanostructure composite electrodes based on a nickel foam current collector
Summary
Electric double-layer capacitors (EDLCs) are charge-storage devices with a high power density, long cyclic life and low maintenance cost. 1-4 They fill the gap between batteries (high energy density) and electrolytic capacitors (high power density). 5, 6 Such properties make them potentially useful for a wide range of applications such as hybrid vehicles, cordless electric tools, memory back-up, cellular phones, medical devices, military and consumer electronics.[7]. Much attention has been given to developing novel nanostructured materials with high specific surface area (SSA), controlled pore size distribution, increased operating voltage and comprehensive understanding of electrode/electrolyte interfaces at the nanoscale.[2, 10,11,12] This led to many research activities focused on developing electrode materials for supercapacitors that are capable of storing more energy without sacrificing cyclic life and power density. The large specific surface area of GF ensured a large loading capacity for MnO2 nanostructures and a large active surface area for rapid charge transfer and a large double layer capacitance They showed that graphene-metal oxides composites offered good adhesion for the metal oxide particles, which prevented detachment and agglomeration, thereby leading to improved capacitance in the three electrode configuration. Hydrothermal synthesis of MnO2 on graphene was performed with the goal of combining double-layer and redox capacitance for achieving high energy and power densities in one device
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