342
Electrochemical Supercapacitors for Energy Storage and Delivery
supported on graphene oxide [53]. Incorporation of metal oxides into CNTbased electrodes is a commonly investigated approach.
Direct deposition of metal oxide species directly onto the surfaces of
CNTs has been reported by techniques such as electrodeposition [54,55],
microwave-assisted deposition [46], wet chemistry [56], and hydrothermal
treatment [50]. Direct deposition creates a good interface between the two
materials and allows the CNTs to act as electronic charge carriers with
minimal interfacial resistance. While maintaining the inherent advantages
of using CNTs as backbone structures, as discussed previously, these onedimensional nanostructures can also be fabricated into aligned electrode
morphologies exhibiting enhanced electrolyte transport and charge storage capabilities. The CNT arrangements can serve to suppress volumetric
changes occurring during charge and discharge cycles and dramatically
improve the cyclabilities of metal oxide materials.
To offset the drawback of low surface areas of CNTs, graphene-based
composite materials can be formed to overcome this limitation by providing satisfactory surface areas and mechanical and electronic properties.
Metal oxide species can be deposited directly on graphene surfaces to form
complementary composite materials [24,50]. For example, manganese oxides
with varying morphologies were deposited onto graphene by an aqueous
precipitation method [24]. Specific capacitances for these composite materials exceeded those for the individual constituents and demonstrated the
impacts of synthesis conditions and composite morphologies.
With this class of composite materials, graphene can provide electronically
conductive pathways and act as a buffer in an electrode structure to mitigate
the effects of volumetric changes during operation. Metal oxide species may
serve as spacers to suppress agglomerations of graphene. When fabricated
into electrode structures, these composite materials exhibit porous structures that are conducive to electrolyte access. The expected drop in prices of
CNTs and graphene, along with the development of improved manufacturing technologies, may make these composites commercially viable alternative materials for ES electrodes.
The potential for application of composite materials in ES devices is
remarkable. Coupling the distinct charge storage mechanisms of carbons
and psuedocapacitive materials can allow researchers to achieve breakthroughs in energy storage capacitances while overcoming the challenges
of poor cyclability. To do so, scientists must further their fundamental
understanding of the behaviors of this broad class of composite materials during design and fabrication. The investigation of novel composite
arrangements with unique morphologies and electrode architectures provides promise for future ES research and development. Furthermore, the
physical properties of the electrode materials utilized should be tailored
to the specific type of electrolyte utilized. Electrode materials exhibit
very different performances in aqueous and organic electrolytes with
different ions.
Electrochemical Supercapacitors for Energy Storage and Delivery
supported on graphene oxide [53]. Incorporation of metal oxides into CNTbased electrodes is a commonly investigated approach.
Direct deposition of metal oxide species directly onto the surfaces of
CNTs has been reported by techniques such as electrodeposition [54,55],
microwave-assisted deposition [46], wet chemistry [56], and hydrothermal
treatment [50]. Direct deposition creates a good interface between the two
materials and allows the CNTs to act as electronic charge carriers with
minimal interfacial resistance. While maintaining the inherent advantages
of using CNTs as backbone structures, as discussed previously, these onedimensional nanostructures can also be fabricated into aligned electrode
morphologies exhibiting enhanced electrolyte transport and charge storage capabilities. The CNT arrangements can serve to suppress volumetric
changes occurring during charge and discharge cycles and dramatically
improve the cyclabilities of metal oxide materials.
To offset the drawback of low surface areas of CNTs, graphene-based
composite materials can be formed to overcome this limitation by providing satisfactory surface areas and mechanical and electronic properties.
Metal oxide species can be deposited directly on graphene surfaces to form
complementary composite materials [24,50]. For example, manganese oxides
with varying morphologies were deposited onto graphene by an aqueous
precipitation method [24]. Specific capacitances for these composite materials exceeded those for the individual constituents and demonstrated the
impacts of synthesis conditions and composite morphologies.
With this class of composite materials, graphene can provide electronically
conductive pathways and act as a buffer in an electrode structure to mitigate
the effects of volumetric changes during operation. Metal oxide species may
serve as spacers to suppress agglomerations of graphene. When fabricated
into electrode structures, these composite materials exhibit porous structures that are conducive to electrolyte access. The expected drop in prices of
CNTs and graphene, along with the development of improved manufacturing technologies, may make these composites commercially viable alternative materials for ES electrodes.
The potential for application of composite materials in ES devices is
remarkable. Coupling the distinct charge storage mechanisms of carbons
and psuedocapacitive materials can allow researchers to achieve breakthroughs in energy storage capacitances while overcoming the challenges
of poor cyclability. To do so, scientists must further their fundamental
understanding of the behaviors of this broad class of composite materials during design and fabrication. The investigation of novel composite
arrangements with unique morphologies and electrode architectures provides promise for future ES research and development. Furthermore, the
physical properties of the electrode materials utilized should be tailored
to the specific type of electrolyte utilized. Electrode materials exhibit
very different performances in aqueous and organic electrolytes with
different ions.