Two hydrogen-bonded organic frameworks with imidazole encapsulation: Synthesis and proton conductivity

Article abstract of DOI:10.1021/acs.cgd.1c00214

On the basis of the carboxylic structure of trimesic acid (TMA) and 5-borono-1,3-benzenedicarboxylic acid (B-BDC), here two hydrogen-bonded organic frameworks (HOFs), HOF 1 (MA-TMA) and HOF 2 (MA-B-BDC), were prepared by reacting melamine (MA) with trimesic acid and 5-borono-1,3-benzenedicarboxylic acid, respectively. The as-prepared HOF 1 and HOF 2 with 3D supramolecular structure exhibit excellent performance in proton transport. AC impedance test shows that the proton conductivities of HOF 1 and HOF 2 reach 3.11 × 10-4 S·cm-1 (343 K, 98% RH) and 4.32 × 10-4 S·cm-1 (323 K, 98% RH), respectively. To increase the proton conductivity, Im@HOF 1 and Im@HOF 2 were obtained by introducing imidazole (Im), which acts as a jumping site for proton transfer. The proton conductivities of Im@HOF 1 and Im@HOF 2 reached 4.12 × 10-4 S·cm-1 (333 K, 98% RH) and 1.20 × 10-3 S·cm-1 (353 K, 98% RH), respectively. This is the first time that guest molecules were introduced into HOFs. The stability and proton conductivity of the HOFs are improved due to the interaction of imidazole with carboxyl groups and water molecules.

Full text of DOI:10.1021/acs.cgd.1c00214

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Two Hydrogen-Bonded Organic Frameworks with Imidazole
Encapsulation: Synthesis and Proton Conductivity
Biao-Biao Hao, Xin-Xin Wang, Chen-Xi Zhang,* and Qinglun Wang*
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ABSTRACT: On the basis of the carboxylic structure of trimesic
acid (TMA) and 5-borono-1,3-benzenedicarboxylic acid (B-BDC),
here two hydrogen-bonded organic frameworks (HOFs), HOF 1
(MA-TMA) and HOF 2 (MA-B-BDC), were prepared by reacting
melamine (MA) with trimesic acid and 5-borono-1,3-benzenedi-
carboxylic acid, respectively. The as-prepared HOF 1 and HOF 2
with 3D supramolecular structure exhibit excellent performance in
proton transport. AC impedance test shows that the proton
conductivities of HOF 1 and HOF 2 reach 3.11 × 10−4 S·cm−1
(343 K, 98% RH) and 4.32 × 10−4 S·cm−1 (323 K, 98% RH),
respectively. To increase the proton conductivity, Im@HOF 1 and
Im@HOF 2 were obtained by introducing imidazole (Im), which
acts as a jumping site for proton transfer. The proton conductivities
of Im@HOF 1 and Im@HOF 2 reached 4.12 × 10−4 S·cm−1 (333 K, 98% RH) and 1.20 × 10−3 S·cm−1 (353 K, 98% RH),
respectively. This is the first time that guest molecules were introduced into HOFs. The stability and proton conductivity of the
HOFs are improved due to the interaction of imidazole with carboxyl groups and water molecules.
Compared with MOFs and COFs, HOFs are formed
through the interaction of hydrogen-bonding forces.19−23
HOFs have high proton conductivity but poor stability for
the weak hydrogen bonds.24−26 Therefore, this shortcoming
limits their use under high-temperature conditions. Selective
introduction of guest molecules27,28 can increase the number
of hydrogen bonds and the stabilities of HOFs.29−31 The large
number of hydrogen-bond networks inside HOFs play a key
role in the stability of the structure and proton conduc-
tion.32−37 Therefore, it is particularly important to improve the
proton conduction characteristics and stabilities of these
materials.38−44
Here, two types of HOFs are synthesized through the
reaction of melamine with trimesic acid and 5-borono-1,3-
benzenedicarboxylic acid, respectively. To increase proton
conductivity, Im@HOF 1 and Im@HOF 2 were obtained by
introducing imidazole through vapor diffusion.45,46 It is found
that Im@HOF 2 achieved a high proton conduction
performance of 1.20 × 10−3 S·cm−1 (353 K, 98% RH),
which is nearly 3 times higher than that of HOF 2. This
1. INTRODUCTION
With the development of science and technology, emphasis on
environmental improvement becomes increasingly crucial.1
Fuel cells can directly convert chemical energy into electric
energy with the characteristics of high conversion rate and no
pollution, which has a great prospect of development and
application in many aspects.2−5 Proton-exchange membrane
(PEM) is an important part of proton-exchange fuel cells,6,7 as
it isolates the filling fuel at the poles, thereby affecting the
transport of electrons. An excellent PEM can maintain a good
proton conduction path so that protons can reach the cathode
through the membrane and react to release energy. Good
stability and efficient proton conduction ability are necessary
for proton-exchange membranes. Therefore, the study of
proton-exchange membrane is of great significance.8 For
example, Nafion membranes have excellent proton conductiv-
ities;9−11 however, water loss at high temperatures leads to a
sharp decrease in conductivity. Moreover, high synthesis cost
would limit the application of Nafion membranes in fuel cells.
Since then, low-cost aromatic polymers have been widely
studied as alternatives to perfluorinated sulfonic acid proton-
exchange membranes.12,13 However, films of this type are
prone to swell under high humidity and are unstable under
high temperatures. To solve the problems of costs and
stabilities, metal−organic frameworks (MOFs), covalent
organic frameworks (COFs), and hydrogen-bonded organic
frameworks (HOFs) are used and discovered with great
significance to proton conductivity.14−18
Received: February 23, 2021
Revised: May 27, 2021
Published: June 4, 2021
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Figure 1. (a) Unit of network structure in the plane, (b) layered structures connected by hydrogen bonds, and (c) 3D structure of HOF 1 with
holes.
(m); Im@HOF 2: 3357 (m), 3334 (m), 3132 (s), 2844 (m), 1650
(s), 1371 (m), 1190 (m), 1027 (m), 815 (m), 703 (m).
method of doping HOFs is first proposed here and will have
great significance for future work.
2.5. Characterization of FTIR, PXRD, and N2 Adsorption. A
sheet made up of the sample and KBr was used to carry out Fourier
transform infrared (FTIR) spectroscopy study (Bruker Tensor 27). At
293 K, a Bruker D8 instrument was used to record X-ray powder
diffraction patterns on the synthesized material in the 2θ angle range
of 5−50°. The nitrogen adsorption test was carried out with
Autosorb-IQ-MP (Quantachrome) at −196 °C.
2. EXPERIMENTAL SECTION
2.1. Materials. Melamine (purity 99%) was purchased from
Aladdin Company. Trimesic acid (98%) was purchased from Aladdin
Company. Imidazole (99%) was purchased from Shanghai Bi De
Pharmaceutical Technology Company.
2.6. Proton Conduction Measurement. The obtained HOFs
were ground into powder and compressed by a tablet machine to
obtain small disks with a thickness of about 0.5 mm. Both sides of the
disk were evenly coated with carbon conductive glue and fixed with
electrodes in a sealed environment with different humidities.
Humidity was controlled by different saturated salt solutions of
NaNO2 (65% RH), NaCl (75% RH), KCl (86% RH), KNO3 (93%
RH), and K2SO4 (98% RH). The materials were kept for 24 h under
the corresponding humidity before the AC impedance test. The
calculation formula is as follows
2.2. Synthesis of 5-Borono-1,3-benzenedicarboxylic Acid. 5-
Borono-1,3-benzenedicarboxylic acid was synthesized according to
the method in the previous article, with slight modifications.47
A
quantity of 1.05 g (7.14 mmol) of 3,5-dimethylphenylboronic acid
and 0.5184 g (14.48 mmol) of NaOH were dissolved in 100 mL of
deionized water/tert-butanol solution (v/v = 1:1) and heated to 40
°C before 0.5 g of potassium permanganate was added. When the
color of the solution faded, 6.83 g of potassium permanganate was
added seven times, and the solution was mixed well and heated to 50
°C for 3 h. Once the color of the solution turned brown, the solution
was filtered and the residue was rinsed with hot water. The obtained
filtrate was concentrated to 20 mL under vacuum and acidified by
adding concentrated hydrochloric acid to pH = 1. 5-Borono-1,3-
benzenedicarboxylic acid was thus obtained as a white solid and
washed with a lot of water and then dried in a vacuum environment.
σ = d/SR
Here, σ is the proton conductivity (S·cm−1), d is the thickness of the
sheet (cm), S is the surface area of the sheet (cm2), and R is the
resistance of the sheet (Ω).
1
Yield: 1.01 g, 69.1%. H NMR (CDCl3): δ (ppm) 8.39 (br s, 2H),
The corresponding activation energy can be calculated by testing
the proton conductivity at different temperatures and humidities,
which can be used to discuss and study the mechanism of proton
conduction. The specific Arrhenius equation is as follows
8.53 (s, 1H), 8.59 (s, 2H), 13.32 (br s, 2H).
2.3. Preparation of HOF 1 and HOF 2. HOF 1 was synthesized
according to the literature.48,49 Melamine (0.063 g, 0.5 mmol) and
trimesic acid (0.105 g, 0.5 mmol) were placed in a 100 mL round-
bottom flask, separately. A volume of 50 mL of deionized water was
added, and the two solutions were stirred for 0.5 h at 70 °C. After
cooling down to room temperature, the two solutions were mixed
together and stirred for 1 h. The white blocky substance called HOF 1
was obtained by filtering and washing with deionized water. Finally,
HOF 1 was dried under vacuum at 50 °C. In the same way, using 5-
borono-1,3-benzenedicarboxylic acid instead of trimesic acid, the
blocky substance HOF 2 was obtained. Elemental Anal. Calcd for
HOF 1 C12H18N6O19: C, 26.1%; H, 3.2%; N 15.2%; Found: C, 26.3%;
H, 3.8%; N, 16.2%; Calcd for HOF 2 C11H19N6O19B: C, 24.0%; H,
3.4%; N, 15.2%; Found: C, 23.7%; H, 3.6%; N, 15.5%; FTIR (KBr,
cm−1) for HOF 1: 3390 (s), 3243 (m), 1740 (m), 1658 (m), 1280
(s), 759 (m), 686 (m); HOF 2: 3339 (m), 1652 (m), 1618 (w), 1553
(m), 775 (s), 714 (m), 577 (m).
2.4. Preparation of Im@HOF 1 and Im@HOF 2. A quantity of
0.6 g of HOF 1 was placed in a 50 mL beaker, which was placed in a
sealed container containing 5 g of imidazole powder. The container
was heated at a temperature of 120 °C for 72 h in a vacuum oven and
a slightly yellowish product of Im@HOF 1 was formed. Using the
same method, the corresponding Im@HOF 2 was formed by
replacing HOF 1 with HOF 2. Elemental Anal. Found for Im@
HOF 1: C, 43.9%; N, 25.6%; H, 4.8% (yield = 60% based on N);
Im@HOF 2: C, 42.1%; N, 23.4%; H, 4.1% (yield = 44% based on N);
FTIR (KBr, cm−1) for Im@HOF 1: 3357 (s), 3119 (m), 3036 (m),
2847 (m), 1677 (s), 1348 (m), 1153 (m), 1083 (m), 859 (m), 733
σT = σ0 exp(−Ea/kBT)
where σ0 is the prereference factor, Ea is the activation energy, and kB
is the Boltzmann constant.
3. RESULTS AND DISCUSSION
3.1. Structural Characterizations. Since trimesic acid
and melamine are acidic and basic compounds, respectively, it
is easy to form a large number of hydrogen bonds in HOF 1,
which increases the stability of the HOFs.50 According to the
previous reports,47 its hydrogen bond structure is shown in
Figure 1. Based on HOF 1,47 the structure of HOF 2 is
obtained by changing a carboxyl group in trimesic acid to a
boronic acid group using Materials Studio 8.0.51 There are four
different types of hydrogen bonds (Figure 1a) that constitute
the network framework of HOF 1 and HOF 2.48,52 A plane
unit of HOF 1 is formed by four melamine and two trimesic
acid molecules through hydrogen bonding (Figure 1a). Two
hydrogen bonds can be formed by an amino group from
melamine in the cavity and two water molecules. One-
dimensional chains of hydrogen bonds are formed by adjacent
water molecules in pores, which provide support for the
multilayer network structure of HOF 1. In addition, the π−π
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Figure 2. (a) Infrared absorption spectra of HOF 1 (black), Im (green), and Im@HOF 1 (blue). (b) Infrared absorption spectra of HOF 2
(black), Im (green), and Im@HOF 2 (red).
Figure 3. PXRD spectra of (a) HOF 1 and (b) HOF 2 for simulated, as-synthesized, and imidazole doping.
stacking between melamine and trimesic acid also plays an
important role in stabilizing the layered structure of HOF 1
(Figure 1b). In the angle of view perpendicular to the plane
layer, HOF 1 can be seen as a 3D structure with holes (Figure
1c). Compared with HOF 1, the network structure of HOF 2
is not changed except that the boronic acid group has one
more hydroxyl than the carboxyl group, which can form more
hydrogen bonds with water molecules (Figure S1). Hydrogen
bonds can also be formed by the water molecules in the pores
and amino groups from melamine, which provide many proton
conduction pathways.
3.2. Infrared (IR) Absorption Spectrum. The character-
istic absorption wavelengths that occurred at 2848 and 2604
cm−1 belong to imidazole molecules. After being doped with
imidazole, both Im@HOF 1 and Im@HOF 2 show the
characteristic absorption peaks of imidazole molecules in
Figure 2a,b, which indicates that imidazole is successfully
incorporated into the two HOFs.
3.3. TGA and PXRD Patterns. The thermal properties of
HOF 1 and HOF 2 are shown in Figure S2. The weight of
HOF 1 reduces by 5.5% under 95 °C and decreases rapidly by
about 70% under 380 °C. The first weight loss is attributed to
the loss of water molecules in the voids of HOF 1, and the
second large-scale mass loss is attributed to the collapse of the
HOF 1 framework. After imidazole doping, Im@HOF 1 has a
mass loss of 10% at about 180 °C, which proves that Im@HOF
1 has better thermal stability than HOF 1. The higher weight
loss of water molecules proves that the introduction of
imidazole increases the adsorption of water molecules by HOF
1, which is attributed to the formation of hydrogen bonds
between water molecules and N−H of the imidazole structure.
Compared with HOF 1, twice weight losses of HOF 2 and
Im@HOF 2 both occur at 100−150 and 340 °C, respectively
(Figure S2). It is worth noting that Im@HOF 2 has relatively
higher stability because of its smaller weight loss in the range of
100−150 °C, which indirectly proves that the introduction of
imidazole molecules will enhance the stability of HOF 2. The
electron-withdrawing ability of carboxylic acids is stronger than
that of boric acids, which makes its conversion to CO2 easier at
high temperatures, leading to weight losses of 90.9% and 71.4
% for Im@HOF 1 and Im@HOF 2 at 500 K, respectively.
The PXRD spectra of HOF 1 and HOF 2 are compared with
the previous report.49 As shown in Figure 3, the structures of
HOF 1 and HOF 2 maintain good stability before and after
imidazole vapor diffusion, which can be clearly seen from the
PXRD spectrum (Figure 3a,b). The PXRD spectra of Im@
HOF 1 and Im@HOF 2 were analyzed by immersing them in
water at 100 °C and testing their conductivity 5 times. The
result shows that they are stable under high-temperature and
high-humidity conditions (Figure S3).
3.4. Nitrogen Adsorption Properties. Before the
nitrogen adsorption test, HOF 1 and HOF 2 were placed in
a vacuum drying oven at 100 °C for 24 h for activation.
Nitrogen adsorption study reveals that the highest nitrogen
adsorption capacities of HOF 1 and HOF 2 are 117 and 62
cm3·g−1 and the specific surface areas are 10.99 and 6.13 m2·
g−1, respectively. From the adsorption and desorption curves, it
is found that both HOF 1 and HOF 2 belong to the type III
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Figure 4. (a) AC impedance spectrum of HOF 1 at 98% RH and 298−343 K. (b) AC impedance spectrum of Im@HOF 1 under 98% RH and
288−323 K. (c) AC impedance spectrum of HOF 2 at 98% RH and 303−333 K. (d) Proton conductivity of Im@HOF 1 at 98% RH at 298−323
K.
Figure 5. (a) AC impedance spectrum of Im@HOF 2 at 98% RH and 303−353 K. (b) Proton conductivity of Im@HOF 2 at 98% RH and 303−
353 K. (c) Proton conductivity of Im@HOF 2 at room temperature and 65−98% RH. (d) Ea of Im@HOF 2 at 98% RH and 303−353 K.
adsorption (Figure S4), which reveals that the interaction force
between HOFs and nitrogen is relatively weak.26,53 As
expected, the amount of nitrogen adsorbed by Im@HOF 1
and Im@HOF 2 dropped significantly after the introduction of
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imidazole molecules. The nitrogen adsorption capacities of
Im@HOF 1 and Im@HOF 2 are only 10 and 12 cm3·g−1,
respectively, which definitely proves that imidazole has entered
the pores of the material.
3.5. Proton Conductivity Properties. Organic molecular
structures with amino and carboxyl groups are often used to
develop proton-conducting materials at high humidities. HOF
1 and HOF 2 have good proton conductivity owing to their
structures, which feature a large number of carboxyl groups
and an extensive network of hydrogen bonds. The high proton
conductivity of HOF 1 and HOF 2 is verified by the AC
impedance test.
Figure 6. Protons transferred by imidazole in pore species.
Im@HOF 2 has the highest proton conductivity of 1.20 ×
10−3 S·cm−1 at 98% relative humidity and 353 K, which is
about 3 times higher than the proton conductivity of HOF 2
before doping with imidazole (Figure 5a,b), proving that
proton conductivity is successfully improved by the introduc-
tion of imidazole. The proton conductivity of Im@HOF 2
reaches a maximum of 4.32 × 10−4 S·cm−1 when the relative
humidity is 98% at room temperature (Figure 5c). The Ea
values of HOF 2 and Im@HOF 2 are 0.39 and 0.15 eV,
respectively, which also show that the participation of
imidazole reduces the energy required for proton transport
(Figures 5d and S7). It also proves that the proton transfer
mechanisms of HOF 2 and Im@HOF 2 are all Grotthuss
mechanisms. As shown in Table 1, compared with the HOFs
reported in the literature,41−44 the synthesized Im@HOF 2
exhibits relatively high proton conductivity.
Figures 4a, S5, and S6 display the measurement of the
proton conductivity of HOF 1 at different humidities and
temperatures. The Nernst curve of HOF 1 shows that as the
relative humidity increases from 65% RH to 98% RH at room
temperature, the proton conductivity of HOF 1 increases from
1.20 × 10−8 S·cm−1 (298 K, 65% RH) to 4.80 × 10−6 S·cm−1
(298 K, 98% RH). This clearly indicates that water plays a
significant role in the proton conduction pathway. In HOF 2,
the boronic acid group has one more hydroxyl than the
carboxyl group so that it can form hydrogen bonds with more
water molecules, resulting in a higher proton conductivity than
HOF 1. Under the condition of 298 K, the proton conductivity
of HOF 2 also increases from 1.04 × 10−7 S·cm−1 (298 K, 65%
RH) to 1.64 × 10−4 S·cm−1 (298 K, 98% RH) when the
environmental humidity steadily increased (Figure 5c).
With the increase of temperature under humidity at 98%, the
highest proton conductivities of HOF 1 and HOF 2 are 3.11 ×
10−4 S·cm−1 (343 K, 98% RH) and 4.32 × 10−4 S·cm−1 (323
K, 98% RH), respectively (Figures 4a and S5). Such high
proton conductivity mainly depends on the interaction of a
large number of internal hydrogen bond network frameworks
and water molecules.
In addition, many previous works involved imidazole doped
in membranes and MOFs have been reported to improve the
conductivity of protons.16−18 There are two scientific argu-
ments: one holds that the rotation of the central axis of the
imidazole molecule transfers protons, and the other is that the
conjugated hydrogen bonds in the molecule accelerate H+
transmission.7,8,15 Considering that the 1D hydrogen bond
chains are formed by the water molecules and amino groups
from melamine in the cavities, the role of imidazole in our
work should be a rotary carrier belonging to the first argument.
Im@HOF 1 and Im@HOF 2 are obtained through the vapor
diffusion method, and the AC impedance test is performed
(Figures 4b and 5a). The proton conductivity of Im@HOF 1
increases from 2.09 × 10−4 S·cm−1 (303 K, 98% RH) to 4.12 ×
10−4 S·cm−1 (333 K, 98% RH) in the temperature range of 298
to 333 K under 98% relative humidity (Figure 4d). As
expected, Im@HOF 1 also shows an upward trend in its
proton conductivity as the temperature increases. The proton
conductivity of Im@HOF 1, i.e., 2.09 × 10−4 S·cm−1 (303 K,
98% RH), is 2 orders of magnitude higher than the proton
conductivity of HOF 1, i.e., 4.80 × 10−6 S·cm−1 (298 K, 98%
RH) of HOF 1 (Figure S5), which indicates that imidazole is
successfully doped to receive and deliver protons (Figure 6).
The Ea values of HOF 1 are 0.50 eV (298−313 K) and 0.71 eV
(313−338 K), while that of Im@HOF 1 is 0.28 eV (Figure
S7), which indicates that imidazole provides a proton jumping
site during proton conduction and the mechanism of proton
conduction changes from the vehicle mechanism to the
Grotthuss mechanism.
Table 1. Summary of Proton Conductivities (S·cm−1) for
HOFs
network
HOF
structure
σ (S·cm−1
3.4 × 10−6
)
Ea (eV)
ref
HOF-6a
3D
2D
2D
3D
3D
3D
3D
3D
3D
3D
3D
_
37
38
38
39
39
39
39
40
HOF-GS-10
HOF-GS-11
CPOS-1
CPOS-2
CPOS-3
CPOS-4
HOF-H3L
HOF 1
Im@HOF 1
HOF 2
Im@HOF 2
7.5 × 10−3 0.489
1.8 × 10−2 0.135
1.0 × 10−2 0.93
2.2 × 10−2 0.61
3.3 × 10−4 0.62
7.4 × 10−4 0.82
6.91 × 10−5 0.68
a
b
3.11 × 10−4 0.50, 0.71
4.12 × 10−4 0.28
4.32 × 10−4 0.39
1.20 × 10−3 0.15
this work
this work
this work
this work
3D
b
a
For T = 298−313 K. For T = 313−338 K.
3.6. Proton Conduction Mechanism. Proton transfer in
proton conductive materials has been extensively studied,
including two proton transfer pathways, which are determined
by the activation energy (Ea). When Ea > 0.4 eV, it is
considered to be the vehicle mechanism, and when Ea < 0.4 eV,
it is considered to be the Grotthuss mechanism. According to
the vehicle mechanism, the proton is carried to the destination
by a single carrier, whereas the Grotthuss mechanism indicates
that the proton is transmitted to each other by the cooperation
of multiple carriers.54,55 As shown in Figure 6, a large number
of pores in HOF 1 and HOF 2 are filled by imidazole
molecules. The one-dimensional proton hydrogen bond
channels are formed by the interaction of imidazole with
hydroxyl and amino groups from water and melamine
molecules (Figure S8), respectively. Protons can be received
by imidazole molecules and then transferred to form
protonated water molecules through hydrogen bonding,
maintaining the transmission of protons. The activation
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energies of HOF 1 and HOF 2 are 0.50 (298−313 K)/0.71 (at
313−338 K) and 0.39 eV, while the activation energies of Im@
HOF 1 and Im@HOF 2 are 0.28 and 0.15 eV at 98% relative
humidity, respectively, which fully demonstrate that imidazole
acts as a proton carrier and reduces the energy required for
migration in the process.56−58
ACKNOWLEDGMENTS
■
This work was supported by the National Natural Science
Foundation of China (Nos. 21771111, 21371104, 20771081,
21101096, and 21471084) and Tianjin Research Innovation
Project for Postgraduate Students (2020YJSS051).
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4. CONCLUSIONS
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In summary, we have successfully synthesized two HOFs that
have high proton conductivity. Moreover, the imidazole was
successfully introduced into the pores of these two HOFs
through the vapor diffusion method to further improve the
proton conductivity. Finally, the proton conductivity of Im@
HOF 1 and Im@HOF 2 reached the highest values of 4.12 ×
10−4 S·cm−1 (333 K, 98% RH) and 1.20 × 10−3 S·cm−1 (333
K, 98% RH), respectively. The study shows that imidazole has
a very significant promotion effect on proton conductivity. The
strategy of doping HOFs was used for the first time to improve
the proton conductivity of HOFs, which has a guiding
significance for the doping and modification of HOFs in the
future.
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.cgd.1c00214.
■
sı
Structure of HOF 2; TGA images; comparison of proton
conduction values; comparison of Ea; nitrogen adsorp-
tion isotherms; and structure of 1D chain formed by
water molecules through hydrogen bonds (PDF)
AUTHOR INFORMATION
Corresponding Authors
■
Chen-Xi Zhang − College of Chemical Engineering and
Materials Science, Tianjin University of Science and
Technology, Tianjin 300457, P. R. China; Key Laboratory of
Brine Chemical Engineering and Resource Eco-utilization,
Tianjin University of Science and Technology, Tianjin
300457, P. R. China; orcid.org/0000-0003-3383-9112;
Email: zcx@tust.edu.cn
Qinglun Wang − College of Chemistry, Nankai University,
Tianjin 300071, P. R. China; Key Laboratory of Advanced
Energy Materials Chemistry (Ministry of Education), Nankai
University, Tianjin 300071, P. R. China; orcid.org/0000-
0002-0983-6280; Email: wangql@nankai.edu.cn
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Biao-Biao Hao − College of Chemical Engineering and
Materials Science, Tianjin University of Science and
Technology, Tianjin 300457, P. R. China
Xin-Xin Wang − College of Chemical Engineering and
Materials Science, Tianjin University of Science and
Technology, Tianjin 300457, P. R. China
Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.cgd.1c00214
Author Contributions
All authors contributed to the discussion and writing of the
manuscript. The final version was approved by all authors.
Notes
The authors declare no competing financial interest.
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