340
Electrochemical Supercapacitors for Energy Storage and Delivery
[22,23] with the α crystallographic structure providing the highest energy
storage capabilities [22]. Moreover, the impact of morphology has also been
demonstrated [23,24] and deemed capable of tailoring the specific capacitances of these materials. To this end, various manganese oxide nanostructures have been investigated. Nanorods [25], nanoplates [26], and needle-like
morphologies [24] demonstrated promising performance improvements.
Another common technique for improving the performances of transition metal oxides is using systems containing two or more metal species.
These complex transition metal oxide systems exhibit beneficial electronic
properties and show significant promise as psuedocapacitive materials.
These include high surface area microporous NiCo 2 O 4 spinel material
[27,28], FeTiO 3 [29], and MnFe 2 O 4 [30]. The complementary redox and electronic properties of these materials render their application in ES devices
very promising.
Introducing nitride or sulfide species also has the potential for marked
performance enhancement [31–34]. Further work is required to clearly understand the performances of these materials and develop different formulations and structures. Operational stability must also be considered. Issues
such as volumetric changes during cycling and electrochemical instabilities
will compromise the overall performance of a device.
9.3.3.2 Conductive Polymers
Conductive polymers can provide excellent capacitive storage capabilities
and good electronic conductivity. They also are capable of storing energy
throughout the bulk of a material, and thus nanostructure control is a
required strategy to provide mass transport and ion access to improve the
utilization of internal redox centers. Steady progress has been made on this
front, for example, by developing aligned polyaniline nanowires [35] to
improve reactant access.
However, the practical applicability of conductive polymers as psuedocapacitive materials is limited primarily by inherent instabilities caused by
their specific redox charge storage mechanisms. Volumetric changes and
irreversibilities induced during cycling will also limit the long term operational stability of conductive polymer-based electrodes. The literature notes
that the impacts of these inherent challenges may be mitigated somewhat by
methods such as incorporation of substituent groups [36–38] and ultrasonic
irradiation during polymer processing [39,40].
Despite these advancements, the use of stand-alone conductive polymers will remain in the research and development phase unless significant
improvements can be made. It is possible to composite conductive polymers
with electric double-layer carbon-based materials. This is a viable approach
to overcome the inherent disadvantages of conductive polymer materials
while capitalizing on their specific energy storage capabilities. This promising approach will be discussed in the following section.
Electrochemical Supercapacitors for Energy Storage and Delivery
[22,23] with the α crystallographic structure providing the highest energy
storage capabilities [22]. Moreover, the impact of morphology has also been
demonstrated [23,24] and deemed capable of tailoring the specific capacitances of these materials. To this end, various manganese oxide nanostructures have been investigated. Nanorods [25], nanoplates [26], and needle-like
morphologies [24] demonstrated promising performance improvements.
Another common technique for improving the performances of transition metal oxides is using systems containing two or more metal species.
These complex transition metal oxide systems exhibit beneficial electronic
properties and show significant promise as psuedocapacitive materials.
These include high surface area microporous NiCo 2 O 4 spinel material
[27,28], FeTiO 3 [29], and MnFe 2 O 4 [30]. The complementary redox and electronic properties of these materials render their application in ES devices
very promising.
Introducing nitride or sulfide species also has the potential for marked
performance enhancement [31–34]. Further work is required to clearly understand the performances of these materials and develop different formulations and structures. Operational stability must also be considered. Issues
such as volumetric changes during cycling and electrochemical instabilities
will compromise the overall performance of a device.
9.3.3.2 Conductive Polymers
Conductive polymers can provide excellent capacitive storage capabilities
and good electronic conductivity. They also are capable of storing energy
throughout the bulk of a material, and thus nanostructure control is a
required strategy to provide mass transport and ion access to improve the
utilization of internal redox centers. Steady progress has been made on this
front, for example, by developing aligned polyaniline nanowires [35] to
improve reactant access.
However, the practical applicability of conductive polymers as psuedocapacitive materials is limited primarily by inherent instabilities caused by
their specific redox charge storage mechanisms. Volumetric changes and
irreversibilities induced during cycling will also limit the long term operational stability of conductive polymer-based electrodes. The literature notes
that the impacts of these inherent challenges may be mitigated somewhat by
methods such as incorporation of substituent groups [36–38] and ultrasonic
irradiation during polymer processing [39,40].
Despite these advancements, the use of stand-alone conductive polymers will remain in the research and development phase unless significant
improvements can be made. It is possible to composite conductive polymers
with electric double-layer carbon-based materials. This is a viable approach
to overcome the inherent disadvantages of conductive polymer materials
while capitalizing on their specific energy storage capabilities. This promising approach will be discussed in the following section.