Alkaline Anion-Exchange Membranes Containing Mobile Ion Shuttles

Article abstract of DOI:10.1002/adma.201506199

A new class of alkaline anion-exchange membranes containing mobile ion shuttles is developed. It is achieved by threading ionic linear guests into poly(crown ether) hosts via host-guest molecular interaction. The thermal- and pH-triggered shuttling of ion

Full text of DOI:10.1002/adma.201506199

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Alkaline Anion-Exchange Membranes Containing Mobile
Ion Shuttles
Xiaolin Ge, Yubin He, Michael D. Guiver, Liang Wu,* Jin Ran, Zhengjin Yang,
and Tongwen Xu*
Anion-exchange membranes (AEMs) are polymer electrolytes
that conduct anions, such as OH−, Cl−, SO42−, as they contain
positively charged groups bound covalently to polymer back-
bones.[1] Over the last decades, AEMs have been widely used
on a large industrial scale in processes such as diffusion dial-
ysis, electrodialysis, electrolysis, for seawater desalination, the
treatment of industrial effluents, and chlorine–alkaline produc-
tion.[2] More recently, to reduce reliance on fossil fuels, there
has been increasing interest in the use of AEMs in energy con-
version and storage systems, such as reverse electrodialysis,[3]
polymer electrolyte fuel cells,[4] microbial fuel cells,[5] and redox
flow batteries.[6] In particular, the alkaline anion-exchange
membrane fuel cell (AAEMFC) is now considered as one of
the most promising green energy-conversion technologies for
stationary and mobile applications due to the high fuel conver-
sion efficiency at high pH and low cost stemming from their
ability to operate in basic conditions using nonprecious metal
catalysts.
However, one key impediment to commercialization is
insufficient hydroxide ion (OH−) conductivity of the central
AAEM component. Prior investigations have noted that AAEMs
in which the cationic groups are commonly connected to the
polymer backbones via short linkages (often CH2 , referred
to as main-chain-type AAEMs) do not exhibit sufficiently high
conductivities. Elongating the length of the link should, in
principle, enhance the conductivities of AAEMs (referred to as
comb-shaped AAEMs) by assisting in the formation of a highly
ordered phase-segregated morphology; this morphology gen-
erally results from the enthalpy associated with the demixing
of incompatible polymer backbones and ionic side chains.[7–20]
The ionic side chains tend to self-assemble to construct hydro-
philic “channels,” wherein OH− transport is widely considered
to proceed via a Grotthuss-type mechanism (schematic illus-
trated in Figure 1A).[21–24] Several researchers have proposed
that hydroxide ions are naturally hydrated by hydrogen bonding
with water molecules to form different hydration complexes
(inactive OH−(H2O)4, active OH−(H2O)3). The continuous inter-
conversion between hydration complexes driven by fluctua-
tions in the solvation shell of the hydrated ions results in facile
OH− transport (Figure 1A).[25–29] In the “channels” of covalent
comb-shaped AAEMs, the cationic groups on the side chains
are highly hydrophilic and can freely rotate to enhance such
fluctuations via electrostatic interactions with hydrated OH−;
however, the remainder of the side chains are hydrophobic and
more rigid, with minor contributions to OH− conduction.[30–33]
Although increasing the ionic content in a covalent comb-
shaped AAEM can help to reach the ostensible goal of “higher
conductivity,” it, in turn, causes undesirable, excessive dimen-
sional swelling from the associated water of hydration. Thus,
increasing the mobility of the side chains, rather than the ionic
content of AAEMs, is a promising strategy for enhancing the
interconversion between hydration complexes without causing
excessive dimensional membrane swelling.
The thermal- and pH-triggered mechanical motion of crown
ether-based polyrotaxane suggests a fundamentally new direc-
tion for developing novel AAEMs with movable side chains.[34,35]
Polyrotaxanes represent a significant class of noncovalently
bonded polymers, in which linear molecular embedded axles
(guests), have mobility through macrocyclic cavities (hosts)
in the main chains.[36–40] One of the striking features of these
polymers compared with covalently bounded polymers is their
structural resemblance to polymer blends, wherein the linear
embedded axle components can reversibly vary the aggrega-
tion and relative spatial positions with respect to changes in the
physical and chemical environment (e.g., temperature and pH).
Inspired by this unique molecular architecture, we report for
the first time AAEMs containing mobile ion shuttles. Comb-
shaped polyrotaxanes were synthesized by threading linear
guests containing two dibenzylammonium centers into an aro-
matic main chain bearing dibenzo[24]crown-8 (DB24C8) cavi-
ties via host–guest molecular recognition, followed by confining
the guest with bulky ammonium end groups (Figure 1B). The
structural characteristics and the beneficial effects of the mobile
ion shuttles on OH− conductivity are investigated in detail.
The comb-shaped polyrotaxane was synthesized as depicted
in Scheme 1. The poly(crown ether) 1d was synthesized
according to Scheme 1A by polyacylation (see Figure S1 in the
Supporting Information).[41–43] The linear side chain guest pre-
cursor (2d) was synthesized by reacting 1,4-bis(aminomethyl)-
benzene with methyl 4-formylbenzoate under reflux in an
argon atmosphere for 24 h, followed by reduction with lithium
X. L. Ge, Y. B. He, Dr. L. Wu, J. Ran,
Dr. Z. J. Yang, Prof. T. W. Xu
CAS Key Laboratory of Soft Matter Chemistry
Collaborative Innovation Center of Chemistry
for Energy Materials
School of Chemistry and Materials Science
University of Science and Technology of China
Hefei 230026, P. R. China
E-mail: liangwu8@ustc.edu.cn; twxu@ustc.edu.cn
Prof. M. D. Guiver
State Key Laboratory of Engines
School of Mechanical Engineering
Collaborative Innovation Center of
Chemical Science and Engineering (Tianjin)
Tianjin University
92 Weijin Road, Tianjin 300072, P. R. China
DOI: 10.1002/adma.201506199
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with hydrobromic acid (HBr) and ammo-
nium hexafluorophosphate (NH4PF6) (see
Scheme S2 and Figure S4 in the Sup-
porting Information). The comb-shaped
−
3d-e•2PF6 •2Br− was obtained by first mixing
poly(crown ether) 1c with the ammonium
−
axle component 2e•2PF6 and then end-
capping the axle termini with bulky tris(2-
ethylhexyl)amine (3a) to prevent diffusional
loss of the side chains (see Scheme S3 and
Figure S5 in the Supporting Information).
Compared with the 1H NMR spectrum of
poly(crown ether) containing no guest mol-
ecule in Figure 2A, a new ammonium proton
−
signal appears at 9.3 ppm in 3d-e•2PF6 •2Br−
(Figure 2B), indicating that the dibenzylam-
monium guest was encircled by the macrocy-
clic cavities of the poly(crown ether). The per-
centage of guest incorporation was calculated
to be 87.1% by comparing the contents of the
ammonium axles and crown ether moieties
on the basis of the elemental analysis results.
Figure 1. Schematic illustration of (A) hydroxide ion (OH−) transport via the continuous inter-
conversion between hydration complexes. B) Comb-shaped polymer architecture containing
mobile ion shuttles.
aluminum hydride (LiAlH4) (see Scheme S2 and Figure S2
and S3 in the Supporting Information). The terminal hydroxyl
and secondary amine groups were then converted into bromo-
methyl and ammonium groups through sequential reaction
The host–guest polymer is soluble in chloroform (CHCl3),
dimethyl sulfoxide, 1-methyl-2-prrolidinone (NMP), and N,N-
dimethylformamide, but is insoluble in water, even though it
contains ammonium moieties.
Scheme 1. Synthesis of small molecules and polymers. A) Synthesis of poly(crown ether). B) Synthesis of guest side chain precursor. C) Synthesis of
the comb-shaped polyrotaxane AAEM containing mobile ion shuttles.
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the membrane an unusually low-dimensional swelling ratio
(DSR) of 7.5% at 60 °C.
An interesting transparency-change phenomenon was
observed for membranes with different degrees of hydration.
As shown in Figure 3A, the fully hydrated membranes were
translucent after being immersed in water at low temperatures
(30 °C, 40 °C) for 24 h; however, they became opaque when
hydrated in hot water (50 °C). Interestingly, all of the mem-
branes reverted to transparent after being dried (Figure 3A).
The transparency change in the temperatures range of 30 to
80 °C is presented in Figure S7 in the Supporting Informa-
tion. The multiphase morphology of the hydrated membrane
is responsible for this effect. During membrane formation,
ionic guest side chains tend to aggregate to form hydrophilic
domains, which can adsorb water molecules to form “water
pools.” Disrupting the host–guest interaction by heating leads
to the hydrated membrane structurally resembling a polymer
blend, wherein the guest side chain components possibly dis-
solve in the “water pool” and shuttle independently to a cer-
1
Figure 2. Characterization of polymer structures. A) 1H NMR spec-
trum of poly(crown ether) 1d; B) 1H NMR spectrum of polyrotaxane
tain extent (Figure 3B). To confirm this assumption, H NMR
analysis was employed to further evaluate the dynamic behavior
of the guest side chains in the hydrated membrane. Figure 3C
1
3d-e•2PF6−•2Br− with host–guest interactions. C) H NMR spectrum of
polyrotaxane 3d-e•2OH− without host–guest interactions.
1
shows H NMR spectra of the membrane/D2O mixture, where
the spectra were collected as the temperature increased. The
expected proton signals consistent with the guest side chain
were observed. The signal intensities continue to increase with
temperature from 30 to 50 °C, and then remain constant when
further increasing the temperature up to 80 °C (Figure S7, Sup-
porting Information). Moreover, all of the proton signals disap-
pear when the membrane is removed from the D2O (see the
bottom spectrum in Figure 3C). This suggests that the mobile
guest side chains can dissolve in the hydrated domains but
do not undergo diffusive loss from the poly(crown ether) host
because of confinement by the bulky end groups. Notably, the
hydrophilic domains swell slightly in the hydrated state (DSR
of 7.5% at 60 °C in Table S1 in the Supporting Information),
which provides sufficient volume for the local side chain
shuttling. This exceptional feature is expected to endow the
polyrotaxane-based AAEMs with a unique mode of OH− con-
ductivity without the need for a high concentration of charged
anion-exchange groups.
The host–guest interaction between the secondary ammo-
nium moieties and crown ether cavities is known to be stim-
ulus-sensitive as a consequence of the relatively low activa-
tion energy required for breaking the weak interactions.[34–36]
Hence, introduction of a base or heating would be expected to
disrupt the host–guest interactions. Upon treatment with 1 M
aqueous KOH at 25 °C for 24 h, the dibenzylammonium center
was deprotonated back to a neutral amino group, resulting in
the disappearance of the dibenzylammonium proton signal at
9.3 ppm and the appearance of a new proton signal at 5.3 ppm
arising from the neutral amino groups (Figure 2C; Figure S6,
Supporting Information). In addition to the pH stimuli, dif-
ferential scanning calorimetry (DSC) analysis was also used
to investigate the thermal stimuli. The DSC thermogram of
3d-e•2OH− revealed a broad endothermic peak in the tempera-
ture range 40–60 °C (Figure S8, Supporting Information); this
peak is attributed to disruption of the host–guest interactions
between the crown ether and the dibenzylammonium moie-
ties, suggesting the thermally responsive characteristic of this
interaction.
To evaluate the benefits of the mobile shuttles for OH−
conduction, the OH− conductivities of AAEM3d-e•2OH− were
measured as a function of temperature and are depicted
in Figure 4A. The conductivity increases from 58 mS cm−1
at 30 °C and reaches a maximum of 189 mS cm−1 at 90 °C.
Notably, the conductivity–temperature curve shows a nonlinear
increasing trend. The slope of the curve is only 0.71 in the tem-
perature range of 30 to 60 °C, but jumps to 3.27 at the higher
temperature range. The profile is distinctly different from that
of recently reported covalent comb-shaped AAEMs. As shown
in Figure 4B, all curves change in a linear trend, and exhibit
lower slopes than that of AAEM3d-e•2OH− at temperatures higher
than 60 °C. The thermally triggered mobile shuttle behavior of
the guest side chains is responsible for this interesting phe-
nomenon. Base treatment with aqueous KOH disrupts the
host–guest interaction between the backbone and the charged
center-point of the mobile side chain, by removing the charge
on nitrogen. Elevated temperature can provide sufficient energy
Disrupting this interaction imparts the guest side chains
with increased mobility and an increased hydrodynamic radius,
which are both expected to accelerate ion transport in the poly-
rotaxane membrane.
Comb-shaped polyrotaxane-based AAEMs (in the Br− form)
−
were prepared by solution casting the 3d-e•2PF6 •2Br−/NMP
solution (8 wt%). To increase the guest chain mobility, the
resulting Br− from AAEM was treated with 1 M aqueous KOH
at 25 °C for 24 h to deprotonate the central dibenzylammonium
groups back to neutral amino groups, while also converting
the termini into the OH− form for hydroxide ion transport.
This membrane is denoted AAEM3d-e•2OH−, and its properties
are listed in Table S1 (Supporting Information). The resulting
membrane has a relatively low ion-exchange capacity (IEC) of
0.68 mmol g−1 as well as water uptake of 18.4%, which endows
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increase the solvation-shell fluctuations by
breaking the hydrogen bonding in inactive
OH−(H2O)4 complexes, imparting fast OH−
transport capability. Moreover, Figure 4B
also shows that the AAEM3d-e•2OH− exhibits
excellent conductivity—among the highest
reported for polymeric membranes to date—
but has a correspondingly much lower IEC
(0.68 mmol g−1). This result suggests that
the dynamic shuttling behavior of the mobile
side chains, rather than the ionic content,
provides a new approach to achieving high
OH− conduction. It should also be kept in
mind that the AAEMs would quickly con-
−
vert to less conductive CO32−/HCO3 forms
when exposed to CO2 (or air). Even though
OH− conductivity measured in this study
used a set-up probably with a low level of
−
CO2 exclusion, HCO3 conductivity was still
measured to evaluate the reliability of the ion
shuttle concept obtained from OH− conduc-
tivity data above. As shown in Figure S9 in
−
the Supporting Information, HCO3 conduc-
tivity at 30 °C is approximately half of OH−
conductivity and increases remarkably with
the increase in the temperature. Particularly,
it even increases up to 150 mS cm−1 at 90 °C,
slightly lower than OH− conductivity at the
same temperature (180 mS cm−1). Addition-
ally, the ion shuttle membrane also exhibits
favorable conductivity in the Cl− form,
increasing from 30 to 122 mS cm−1 with the
increase in the temperature in the range of
30 to 90 °C. Hence, the results suggest that
this novel ion shuttle AEM is likely to be
applicable to a variety of membrane-based
technologies involving anion conduction.
Besides high OH– conductivity, sufficient
alkaline stability is also required for the
development of AAEMs for AAEMFCs. For
quaternary ammonium (QA)-type AAEMs,
degradation of the QAs by the OH– attack
is unavoidable (via β-hydrogen elimina-
tion or direct nucleophilic substitution at
α-carbon[44,45]). To evaluate the alkaline sta-
bility of the AAEM3d-e•2OH−, an accelerated
alkaline stability test was performed under
harsh conditions (4 M aqueous KOH at 80 °C
for 98 h). Chemical structural changes occur-
Figure 3. Characterization of charged guest molecules in the hydrated membrane. A) Photo-
graphs of hydrated membranes (left) which were immersed in water at different temperatures
(30, 40, and 50 °C) for 24 h, respectively, and dry membranes corresponding to the hydrated
membranes (right). B) Schematic illustration of the dissolution of hydrophilic side chains in the
hydrated membrane. C) 1H NMR spectra of a membrane/D2O mixture, where the temperature
was increased from 30 to 50 °C, and D2O after removing membrane at 25 °C (bottom spec-
trum). The expected proton signals consistent with the guest side chain were observed in the
top three dark spectra. Moreover, all of the proton signals disappear when the membrane is
removed from the D2O (the bottom red spectrum). This suggests that the mobile guest side
chains can dissolve in the hydrated membrane but do not undergo diffusive loss from the
poly(crown ether) host because of confinement by the bulky end groups.
to further promote side chain shuttling. This result is consistent
with the DSC thermogram (see Figure S8 in the Supporting
Information), in which a phase transition of mobile guest side
chains occurs in the temperature range 40–60 °C. Hydroxide
ion transport through AAEMs has long been explained by a
Grotthuss-type mechanism. The continuous interconversion
between hydration complexes (inactive OH−(H2O)4, active
OH−(H2O)3) is driven by fluctuations in the solvation shell of
the hydrated ions. We show that the pH-triggered and thermally
triggered shuttling of the mobile side chains can significantly
ring in the membrane during the test were detected by 1H
NMR spectroscopy, as shown in Figure S10 in the Supporting
Information. The majority of typical proton signals are main-
tained after 30 h exposure to the harsh alkali environment.
However, in the other spectra corresponding to longer exposure
times, the proton signal at 5.3 ppm arising from the neutral
amino groups in the mobile side chains disappears, indicating
that alkaline degradation occurs. Hofmann elimination of the
QA groups caused by OH− attack is the most likely reason.
As discussed in this work, the mobile side chain termini were
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chains via host–guest molecular recognition. The pH- and
thermally triggered enhanced mobility of the side chains was
observed when the host–guest interaction was disrupted upon
treatment with base. While some structural similarities with
conventional covalent comb-shaped AAEMs can be made, the
polymer architecture of the poly(crown ether)s with pH- and
thermally triggered mobile ion shuttles exhibit behavior more
resembling polymer blends, wherein the guest side chains can,
to a certain extent, shuttle independently in the hydrated state.
This exceptional feature endows these AAEMs with excellent
conductivity—among the best reported for covalent AAEMs to
date—but with a much lower IEC. A systematic study on the
relationship between polymer architecture and alkali stability
as well as other properties, e.g., dimensional swelling, bicarbo-
nate ion conductivity, single cell performance, are currently in
progress.
Supporting Information
Supporting Information is available from the Wiley Online Library or
from the author.
Acknowledgements
The authors acknowledge the financial supports from the National Basic
Research Program of China (Grant No. 2012CB932802) and the National
Natural Science Foundation of China (Grant Nos. 21522607, 21490581,
and 21376232).
Received: December 14, 2015
Revised: January 30, 2016
Published online: March 11, 2016
Figure 4. A) Hydroxide ion (OH−) conductivities of AAEM3d-e•2OH− as a
function of temperature; B) OH− conductivities of recently reported cova-
lent comb-shaped AAEMs as a function of temperature (AAEM3d-e•2OH− is
shown for comparison).
[1] M. A. Hickner, A. M. Herring, E. B. Coughlin, J. Polym. Sci., Part B:
Polym. Phys. 2013, 51, 1727.
[2] H. Strathmann, A. Grabowski, G. Eigenberger, Ind. Eng. Chem. Res.
2013, 52, 10364.
end-capped by bulky QA moieties. Hence, degradation of the
head-groups would result in diffusional loss of the side chains,
leading to the disappearance of typical proton signals of the
mobile side chains in the corresponding 1H NMR spectra.
Theoretically, the sterically hindered head-groups might
impede OH− attack. However, this effect might be weakened
under such a harsh alkaline environment (4 M aqueous KOH
at 80 °C). A QA-containing membrane of this type would most
likely maintain structural integrity for a longer time if tested
under more moderate conditions, e.g., 1 M aqueous KOH at
60 °C (a commonly employed test condition for alkaline sta-
bility in the literature). Therefore, one challenge for the ion
shuttle design will be to maintain high OH− conductivity by
preventing the diffusion loss of the shuttle in an alkali environ-
ment. More efforts will be directed toward improving the alkali
stability by introducing more sterically hindered ammonium
groups to impede OH− attack, or replacing the ammonium cat-
ions by other more stable alkaline units.
[3] W. W. Li, H. Q. Yu, Bioresour. Technol. 2015, 196, 677.
[4] J. R. Varcoe, P. Atanassov, D. R. Dekel, A. M. Herring, M. A. Hickner,
P. A. Kohl, A. R. Kucernak, W. E. Mustain, K. Nijmeijer, K. Scott,
T. Xu, L. Zhuang, Energy Environ. Sci. 2014, 7, 3135.
[5] B. E. Logan, M. Elimelech, Nature 2012, 488, 313.
[6] J. Noack, N. Roznyatovskaya, T. Herr, P. Fischer, Angew. Chem. Int.
Ed. 2015, 54, 9776.
[7] S. Gu, R. Cai, T. Luo, Z. Chen, M. Sun, Y. Liu, G. He, Y. S. Yan,
Angew. Chem. Int. Ed. 2009, 48, 6499.
[8] I. Deavin, S. Murphy, A. L. Ong, S. D. Poynton, R. Zeng, H. Herman,
J. R. Varcoe, Energy Environ. Sci. 2012, 5, 8584.
[9] N. Li, M. D. Guiver, W. H. Binder, ChemSusChem 2013, 6, 1376.
[10] N. Li, Y. Leng, M. A. Hickner, C. Y. Wang, J. Am. Chem. Soc. 2013,
135, 10124.
[11] S. S. He, C. W. Frank, J. Mater. Chem. A 2014, 2, 16489.
[12] N. Yokota, M. Shimada, H. Ono, R. Akiyama, E. Nishino,
K. Asazawa, J. Miyake, M. Watanabe, K. Miyatake, Macromolecules
2014, 47, 8238.
[13] J. Pan, C. Chen, Y. Li, L. Wang, L. Tan, G. Li, X. Tang, L. Xiao, J. Lu,
L. Zhuang, Energy Environ. Sci. 2014, 7, 354.
In conclusion, we report a new approach that provides the
first example of an AAEM with a mobile ion shuttle, made
by threading ionic linear chains into poly(crown ether) main
[14] J. Ran, L. Wu, B. Wei, Y. Y. Chen, T. W. Xu, Sci. Rep. 2014, 4, 6486.
[15] J. Si, S. Lu, X. Xu, S. Peng, R. Xiu, Y. Xiang, ChemSusChem 2014, 7,
3389.
©
wileyonlinelibrary.com
Adv. Mater. 2016, 28, 3467–3472
2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
3471

www.advmat.de
www.MaterialsViews.com
[16] A. D. Mohanty, Y. B. Lee, L. Zhu, M. A. Hickner, C. Bae, Macro-
molecules 2014, 47, 1973.
[17] H. S. Dang, E. A. Weiber, P. Jannasch, J. Mater. Chem. A 2015, 3,
5280.
[18] J. Han, Q. Liu, X. Li, J. Pan, L. Wei, Y. Wu, H. Peng, Y. Wang, G. Li,
C. Chen, L. Xiao, J. Lu, L. Zhuang, ACS Appl. Mater. Interfaces 2015,
7, 2809.
[33] A. Vishnyakov, A. V. Neimark, J. Phys. Chem. B 2014, 118, 11353.
[34] P. R. Ashton, R. Ballardini, V. Balzani, I. Baxter, A. Credi,
M. C. T. Fyfe, M. T. Gandolfi, M. Gómez-López, M. V. Martínez-Díaz,
A. Piersanti, N. Spencer, J. F. Stoddart, M. Venturi, A. J. P. White,
D. J. Williams, J. Am. Chem. Soc. 1998, 120, 11932.
[35] M. Arunachalam, H. W. Gibson, Prog. Polym. Sci. 2014, 39,
1043.
[19] W. H. Lee, A. D. Mohanty, C. Bae, ACS Macro Lett. 2015, 4, 453.
[20] H. N. Rao, S. Nam, T. H. Kim, J. Mater. Chem. A 2015, 3, 8571.
[21] P. Choi, N. H. Jalani, R. Datta, J. Electrochem. Soc. 2005, 152, E84.
[22] K. N. Grew, W. K. S. Chiu, J. Electrochem. Soc. 2010, 157, B327.
[23] M. A. Hickner, J. Polym. Sci., Part B: Polym. Phys. 2012, 50, 9.
[24] N. Li, M. D. Guiver, Macromolecules 2014, 47, 2175.
[25] J. S. Wyithe, A. Loeb, Nature 2002, 417, 923.
[26] R. Ludwig, Angew. Chem. Int. Ed. 2003, 43, 258.
[27] D. Asthagiri, L. R. Pratt, J. D. Kress, M. A. Gomez, Proc. Natl. Acad.
Sci. USA 2004, 101, 7229.
[28] M. E. Tuckerman, A. Chandra, D. Marx, Acc. Chem. Res. 2006, 39,
151.
[29] L. Liu, J. Hunger, H. J. Bakker, J. Phys. Chem. A 2011, 115, 14593.
[30] S. J. Paddison, T. A. Zawodzinski, Solid State Ionics 1998, 333–340,
113.
[36] J. Wu, K. C. Leung, D. Benitez, J. Y. Han, S. J. Cantrill, L. Fang,
J. F. Stoddart, Angew. Chem. Int. Ed. 2008, 47, 7470.
[37] J. Araki, T. Kataoka, K. Ito, Soft Matter 2008, 4, 245.
[38] G. De Bo, J. De Winter, P. Gerbaux, C. A. Fustin, Angew. Chem. Int.
Ed. 2011, 50, 9093.
[39] Y. Kohsaka, Y. Koyama, T. Takata, Angew. Chem. Int. Ed. 2011, 50,
10417.
[40] D. Aoki, S. Uchida, T. Takata, ACS Macro Lett. 2014, 3, 324.
[41] H. M. Colquhoun, D. F. Lewis, Polymer 1988, 29, 1902.
[42] M. G. Zolotukhin, M. C. G. Hernandez, A. M. Lopez, L. Fomina,
G. Cedillo, A. Nogales, T. Ezquerra, D. Rueda, H. M. Colquhoun,
K. M. Fromm, A. Ruiz-Trevino, M. Ree, Macromolecules 2006, 39,
4696.
[43] Z. H. Zhang, L. Wu, T. W. Xu, J. Mater. Chem. 2012, 22, 13996.
[44] J. S. Spendelow, A. Wieckowski, Phys. Chem. Chem. Phys. 2007, 9,
2654.
[31] J. K. ClarkII, S. J. Paddison, Electrochim. Acta 2013, 101, 279.
[32] J. A. Elliott, D. S. Wu, S. J. Paddison, R. B. Moore, Soft Matter 2011,
7, 6820.
[45] S. Chempath, B. R. Einsla, L. R. Pratt, C. S. Macomber, J. M. Boncella,
J. A. Rau, B. S. Pivovar, J. Phys. Chem. C 2008, 112, 3179.
©
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