117
6.1 Polymer Nanocomposites
Neat polymer dielectrics can be used, the most common of which are poly
(4- vinylphenol) (PVP) and poly(vinylidene) fluoride (PVDF), as they offer an
advantage in high breakdown strength when compared to other materials used for
capacitor applications. However, the low dielectric constants significantly limit
their application potential. Perovskite ceramic nanoparticles offer higher dielectric
constants and can be combined with polymers to yield improved polymer nanocomposites [116]. In order to increase the processability and effective surface areas,
BaTiO 3 nanoparticles, and modifications thereof, such as Ba 0.5 Sr 0.5 TiO 3 , have been
functionalized with PVP to result in a more homogenous product having an
increased dielectric permittivity of 77 at 1 kHz, 28% higher than when measured
with untreated BaTiO 3 . It was shown that modification of the surface is also important for close contact between the polymer dielectric and ceramic. Here, hydroxyl
groups on the surface of BaTiO 3 nanoparticles served to hydrogen bond with the
fluorine atoms in the polymeric PVDF [117]. Another method to maintain close
contact of the particle and matrix is to graft the matrix material directly onto the
nanoparticles. For example, PVDF copolymer chains were grown off of TiO 2
nanoparticles. These particles could then be easily dispersed into a polymer matrix
and cast into thin films, which resulted in doubling of the energy storage capabilities
(from 3.25 to ~7.0 J/cm
3
) with 50% loading [118].
6.2 MOFs
MOFs present extremely high surface areas and lend themselves well to this application. Some work has been carried out with decomposed or pyrolyzed MOFs to
yield nanoporous metal oxide structures or porous carbon materials that are comparable to activated charcoal [119]. As for previous devices mentioned throughout the
chapter, the framework structure itself can be used as-prepared or modified with
PSM or guests to behave as the electrolyte. Since MOFs themselves typically exhibit
low conductivity, (which results in an increase in the bulk electric resistance of such
devices) PSM or guest incorporation has been utilized most frequently to address this.
Various strategies have been taken to improve MOF–conductor contact, such as
forming nanocrystalline-sized MOFs for increased interaction with the conductor,
or interweaving the conductor through the MOFs. In 2014, Yaghi et al. made
nanocrystalline- sized MOFs (termed nMOFs), which were doped with graphene.
They tested various metal nodes and organic linkers and found that one particular
system, Zr 6 O 4 -(OH) 4 (BPYDC) 6 (BPYDC = 2,20 -bipyridine-5,50 - dicarboxylate,
termed nMOF-867), exhibits an exceptionally high areal capacitance of
5.09 mF cm
−2
. The authors note that this is about six times that of the supercapacitors made from the benchmark commercial activated carbon materials. Furthermore,
performance that is preserved for at least 10,000 charge/discharge cycles
Polymer Nanocomposites for Ion Transport
6.1 Polymer Nanocomposites
Neat polymer dielectrics can be used, the most common of which are poly
(4- vinylphenol) (PVP) and poly(vinylidene) fluoride (PVDF), as they offer an
advantage in high breakdown strength when compared to other materials used for
capacitor applications. However, the low dielectric constants significantly limit
their application potential. Perovskite ceramic nanoparticles offer higher dielectric
constants and can be combined with polymers to yield improved polymer nanocomposites [116]. In order to increase the processability and effective surface areas,
BaTiO 3 nanoparticles, and modifications thereof, such as Ba 0.5 Sr 0.5 TiO 3 , have been
functionalized with PVP to result in a more homogenous product having an
increased dielectric permittivity of 77 at 1 kHz, 28% higher than when measured
with untreated BaTiO 3 . It was shown that modification of the surface is also important for close contact between the polymer dielectric and ceramic. Here, hydroxyl
groups on the surface of BaTiO 3 nanoparticles served to hydrogen bond with the
fluorine atoms in the polymeric PVDF [117]. Another method to maintain close
contact of the particle and matrix is to graft the matrix material directly onto the
nanoparticles. For example, PVDF copolymer chains were grown off of TiO 2
nanoparticles. These particles could then be easily dispersed into a polymer matrix
and cast into thin films, which resulted in doubling of the energy storage capabilities
(from 3.25 to ~7.0 J/cm
3
) with 50% loading [118].
6.2 MOFs
MOFs present extremely high surface areas and lend themselves well to this application. Some work has been carried out with decomposed or pyrolyzed MOFs to
yield nanoporous metal oxide structures or porous carbon materials that are comparable to activated charcoal [119]. As for previous devices mentioned throughout the
chapter, the framework structure itself can be used as-prepared or modified with
PSM or guests to behave as the electrolyte. Since MOFs themselves typically exhibit
low conductivity, (which results in an increase in the bulk electric resistance of such
devices) PSM or guest incorporation has been utilized most frequently to address this.
Various strategies have been taken to improve MOF–conductor contact, such as
forming nanocrystalline-sized MOFs for increased interaction with the conductor,
or interweaving the conductor through the MOFs. In 2014, Yaghi et al. made
nanocrystalline- sized MOFs (termed nMOFs), which were doped with graphene.
They tested various metal nodes and organic linkers and found that one particular
system, Zr 6 O 4 -(OH) 4 (BPYDC) 6 (BPYDC = 2,20 -bipyridine-5,50 - dicarboxylate,
termed nMOF-867), exhibits an exceptionally high areal capacitance of
5.09 mF cm
−2
. The authors note that this is about six times that of the supercapacitors made from the benchmark commercial activated carbon materials. Furthermore,
performance that is preserved for at least 10,000 charge/discharge cycles
Polymer Nanocomposites for Ion Transport