Ultrafast and Stable Proton Conduction in Polybenzimidazole Covalent Organic Frameworks via Confinement and Activation

Article abstract of DOI:10.1002/anie.202101400

Polybenzimidazoles are engineering plastics with superb thermal stability and this specificity has sparked a wide-ranging research to explore proton-conducting materials. Nevertheless, such materials encounter challenging issues owing to phosphoric acid proton carrier leakage and slow proton transport. We report a strategy for designing porous polybenzimidazole frameworks to address these key fundamental issues. The built-in channels are designed to be one-dimensionally extended, unidirectionally aligned, and fully occupied by neat phosphoric acid, while the benzimidazole walls trigger multipoint, multichain, and multitype interactions to spatially confine a phosphoric acid network in pores and facilitate proton conduction via deprotonation. The materials exhibit ultrafast and stable proton conduction for low proton carrier content and activation energy—a set of features highly desired for proton transport. Our results offer a design strategy for the fabrication of porous polybenzimidazoles for use in energy conversion applications.

Full text of DOI:10.1002/anie.202101400

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How to cite:
International Edition: doi.org/10.1002/anie.202101400
German Edition: doi.org/10.1002/ange.202101400
Covalent Organic Frameworks
Ultrafast and Stable Proton Conduction in Polybenzimidazole
Covalent Organic Frameworks via Confinement and Activation
Juan Li, Jing Wang, Zhenzhen Wu, Shanshan Tao, and Donglin Jiang*
Abstract: Polybenzimidazoles are engineering plastics with
superb thermal stability and this specificity has sparked a wide-
ranging research to explore proton-conducting materials.
Nevertheless, such materials encounter challenging issues
owing to phosphoric acid proton carrier leakage and slow
proton transport. We report a strategy for designing porous
polybenzimidazole frameworks to address these key funda-
mental issues. The built-in channels are designed to be one-
dimensionally extended, unidirectionally aligned, and fully
occupied by neat phosphoric acid, while the benzimidazole
walls trigger multipoint, multichain, and multitype interactions
to spatially confine a phosphoric acid network in pores and
facilitate proton conduction via deprotonation. The materials
exhibit ultrafast and stable proton conduction for low proton
carrier content and activation energy—a set of features highly
desired for proton transport. Our results offer a design strategy
for the fabrication of porous polybenzimidazoles for use in
energy conversion applications.
slow proton motion is related to the steric hindrance of
swollen polymer chains. As a result, the materials are unstable
in performance and reach
a
proton conductivity of
À2
À1
10 Scm , which is even one order of magnitude lower than
À1
À1 [1–3]
neat H PO4 ( ꢀ 10 Scm ).
These fatal issues greatly
3
[
3]
deteriorate their practical implementations. Proton conduc-
tion below 1008C under different relative humidity has been
[
4]
well established with Nafion. Compared to proton con-
duction in the presence of water, anhydrous proton transport
is far more difficult to establish as it imposes serve conditions
[1,2]
on the stability of materials.
Covalent organic frameworks (COFs) are a class of
crystalline porous polymer which can develop well-defined
[5,6]
skeletons and ordered pores.
The porous structures with
controlled pore size, shape, environment, and interface render
the COF materials able to load a diversity of different proton
carriers, such as inorganic acids and imidazole-based organic
heterocycles, for the construction of proton-conducting
[
6,7]
systems.
for proton conduction under different humidity.
However, most examples have been developed
[
6,7c,d]
Introduction
The
presence of water facilitates proton conduction, which how-
ever, limits the upper working temperature up to 1008C.
Anhydrous proton conduction enables to operate at temper-
atures above 1008C but examples are limited to only a few
Proton-conducting materials are key to fuel cells that
transform chemical energy to electricity in a direct, green, and
efficient way. Anhydrous proton-conducting materials work
at temperatures above 1008C, enable fast kinetics, and
[
7]
COFs. Designing COFs to merge stability and anhydrous
proton conductivity into one material remains a challenge.
Here we report a strategy for designing porous poly-
benzimidazole COFs to enable stable yet ultrafast anhydrous
proton conduction, which addresses the problems and breaks
the upper proton conductivity limit of traditional polybenzi-
midazole systems. The frameworks are designed to build
specific channel walls which can trigger multipoint, multi-
chain, and multitype interactions to lock and stabilize the
H PO network in pores via spatial confinement and facilitate
[
1,2]
improve efficiency.
Researchers have been focused on
thermally robust engineering plastics in developing anhy-
drous proton-conducting materials. Polybenzimidazoles have
been the focus of typical engineering plastics for constructing
anhydrous proton-conducting systems in conjunction with
neat phosphoric acid (H PO ) as proton carrier over the past
3
4
[
2,3]
six decades. However, polybenzimidazoles hardly organize
to form a structure which can stabilize the H PO network and
3
4
are facing structure-related bottlenecks. For example, the
leakage of H PO is a result of polymer chain swollen while
3
4
proton transport via protonation–deprotonation activation.
We found that the polybenzimidazole COFs in conjunction
3
4
with neat H PO4 exhibit stable and ultrafast proton con-
duction over a wide range of temperatures above 1008C at
[
*] Dr. J. Li, J. Wang, Z. Wu
Institute of Crystalline Materials, Shanxi University
Wucheng Rd No 92, Taiyuan 030006 (China)
3
a low activation energy and a low H PO content. These
3
4
Dr. S. Tao, Prof. D. Jiang
Department of Chemistry, Faculty of Science
National University of Singapore
features are highly desired to be combined in proton-
conducting materials and demonstrate a new platform for
designing porous polybenzimidazole materials for advanced
energy conversions.
3
Science Drive 3, Singapore 117543 (Singapore)
E-mail: chmjd@nus.edu.sg
Prof. D. Jiang
Joint School of National University of Singapore and Tianjin
University, International Campus of Tianjin University
Binhai New City, Fuzhou 350207 (China)
Results and Discussion
Design Strategy. We integrated benzimidazole units into
the backbone to construct stable COFs with one-dimensional
(1D) and unidirectionally aligned channels which are fully
Supporting information and the ORCID identification number(s) for
the author(s) of this article can be found under:
https://doi.org/10.1002/anie.202101400.
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accessible to neat H PO (Figure 1a). One distinct feature is
conventional polybenzimidazoles. As a result, we observed
3
4
that the pore walls are designed to possess imine linkages and
benzimidazole units which stack along the z direction, so that
each channel consists of six single file N chains, three N-H
chains, and three imidazolium cation chains. The imine
linkage owing to the presence of nitrogen atom serves as
hydrogen-bonding acceptor to develop single point hydrogen-
that the COF systems exhibit ultrafast anhydrous proton
conduction over a wide range of temperatures above 1008C.
Synthesis. We synthesized polybenzimidazole TPB-DA-
BI-COF (Figure 1a) by condensing 1,3,5-tris(4-formyl-
phenyl)benzene (TPB) knot with 2,5-diamino-3,4-dimethyl-
benzimidazole (DABI) linker under solvothermal conditions.
In detail, polycondensation of TPB with DABI in a mixture of
o-dichlorobenzene/n-butanol (1/1 vol.) in the presence of
acetic acid (6 M) at 1208C for 3 days produced TPB-DABI-
COF as dark yellow solid with 75% isolation yield (Support-
ing Information).
[7e]
bonding interactions with H PO . In contrast, the benzimi-
3
4
dazole chains trigger multipoint, multichain, and multitype
electrostatic and hydrogen-bonding interactions with the
[
2d,8]
H PO4 network (Figure 1b)
3
to stabilize and lock the
H PO networks in the pores, as evidenced by single crystal
3
4
structure of benzimidazole–H PO complex (Figure 1c). Such
Fourier-transform infrared spectroscopy (FTIR) of TPB-
DABI-COF revealed that the N-H stretching bands at 3323
3
4
a high level of multiple hierarchical interactions has not been
realized with other COFs so far reported. More importantly,
the N atom in the benzimidazole unit is protonated to form
imidazolium cation while H PO is deprotonated to form
À1
and 3401 cm of DABI (Figure 2a, blue curve) and the C=O
À1
vibration band at 1694 cm of TPB (Figure 2a, black curve)
disappeared, suggesting the occurrence of polycondensation
3
4
À
À1
H PO4 anion (Figure 1c), so that the proton network is
activated by the H and open H PO sites to facilitate proton
reaction. The new vibration bands at 1621 cm was assigned
2
+
À
to the C=N bond (Figure 2a, red curve), indicating the
2
4
1
3
conduction. We highlight that this wall configuration offers
the structure basis for stabilizing proton networks in the pores
and for constituting proton-conducting freeways to enable
ultrafast proton transport. Clearly, this strategy merges the
advantages of both COFs and polybenzimidazoles into one
material and enables to address the key fundamental issues of
formation of imine linkage. Solid-state C cross polarization
magic angle spinning nuclear magnetic resonance (CP/MAS
NMR) spectroscopy of TPB-DABI-COF revealed a signal at
12.71 ppm which was assigned to the methyl carbon of the
benzimidazole linker, together with a peak at 141.01 ppm
which was attributed to the carbon atom of the C=N linkage
(
Figure 2b). The high-resolution
transmission electron micrography
HRTEM) showed a clear diffrac-
(
tion pattern (inset) and ordered
channels of 2.5 nm (Figure 2c).
Thermogravimetric analysis dem-
onstrated that it is thermally robust
and does not decompose up to
4
008C under nitrogen (Supporting
Information, Figure S1), which is
comparable to those of polybenz-
[
2]
imidazoles.
Crystalline Structure. The crys-
talline structure and unit cell pa-
rameters of TPB-DABI-COF were
determined by powder X-ray dif-
fraction measurements (PXRD) in
conjunction with structural simula-
tions using density functional theo-
ry tight binding (DFTB +) and
Pawley refinements. TPB-DABI-
COF exhibited a PXRD pattern
with intense peaks at 2.928, 5.028,
5
.758, 7.578, 9.918, and 24.18, which
were assigned to the (100), (110),
200), (210), (220), and (001) facets,
(
respectively (Figure 3a, black
curve). DFTB + calculations re-
vealed
that
TPB-DABI-COF
adopts a space group of P with
unit-cell parameters of a = b =
3
Figure 1. a) Depiction of the polybenzimidazole COF (TPB-DABI-COF). b) Reconstructed structures
of a single layer (top panel) and ten layers (bottom panel) of the TPB-DABI-COF and sites and
vertical single file chains to confine and activate the H PO network. c) Single-crystal structure of the
3
9.4722 ꢀ, c = 4.0861 ꢀ, a = b =
3
4
benzimidazole–H PO complex shows N
ÀH···O hydrogen-bond and electrostatic interactions; one N
908, and g = 1208. The atomistic
coordinates of AA-stacking TPB-
3
4
of the imidazole ring is protonated by H PO . Atom key: N (blue), O (red), H (white).
3
4
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Pawley refinements yielded a PXRD pattern (Figure 3a,
red curve) that is consistent with the experimentally observed
PXRD profile to show only a small difference (Figure 3a,
blue curve) with the RWP and R values of 0.58% and 0.42%,
P
respectively. The presence of the (001) facet at 24.18 reveals
the structural ordering with an interval of 3.689 ꢀ along the z
direction perpendicular to the 2D polymer plane. The
reconstructed crystal structure reveals mesoporous channels
that are extended and aligned across the material while the
pore walls are installed with dense benzimidazole blocks
(Figure 3b,c). This channel configuration paves the chemical
basis for triggering multipoint, multichain, and multitype
hydrogen bonding and electrostatic interactions with the
H PO network in each channel (Figure 1b). Such a network
3
4
[
7]
has not been explored by COFs.
Nitrogen sorption isotherm curves (Figure 3c, red circles)
revealed that TPB-DABI-COF possesses
Emmett–Teller (BET) surface area of 865.2 m g , a pore
size of 2.4 nm, and a pore volume of 1.06 cm g (Figure S2,
Table S2).
a
Brunauer–
2
À1
3
À1
Chemical Stabilities. We examined the chemical stability
by immersing the TPB-DABI-COF samples in THF, boiling
water, and aqueous HCl solution (9 M), respectively. After
seven days, we measured PXRD and observed that TPB-
DABI-COF retains its crystallinity as evidenced by un-
changed peak positions and full width at half maximum
Figure 2. a) FTIR spectra of TPB (black), DABI (blue), and TPB-DABI-
1
3
COF (red). b) Solid-state C CP/MAS NMR spectrum of TPB-DABI-
COF and peak assignment. c) HRTEM image of TPB-DABI-COF. Inset:
the fast Fourier transform (FFT) spectrum.
(Figure S3). Nitrogen sorption measurements revealed that
the porosity of the COF samples is retained under these
conditions (Figure S4). We further investigated the stability of
TPB-DABI-COF in neat H PO by loading H PO into the
3
4
3
4
pores at 1208C for seven days. Surprisingly, TPB-DABI-COF
kept its crystallinity (Figures S3) and porosity (Figure S4).
These results indicate that TPB-DABI-COF is stable to retain
structure and is robust to explore anhydrous proton con-
duction. We further examined the anti-oxidation capability of
TPB-DABI-COF by Fenton test and confirmed that TPB-
DABI-COF hardly changes its crystallinity and porosity
(Figures S3 and S5).
Single Crystal Structure. In order to identify the inter-
actions between H PO and benzimidazole unit, we succeed-
3
4
ed in preparing single crystals of the model complex of
benzimidazole and H PO (Figure 1c; Supporting Informa-
3
4
tion). From the single crystallography (Table S3, CCDC
[9]
1
94985 ), we observed that one nitrogen atom of benzimi-
dazole is protonated to form imidazolium cation while H PO
3
4
Figure 3. a) PXRD patterns of TPB-DABI-COF of the experimentally
observed (black), Pawley refined (red) and their difference (blue),
simulated using the AA (green), and staggered AB (purple) stacking
modes. b) Top and side views of reconstructed structure of TPB-DABI-
COF with seven pores and six layers. Atom key: N (blue), C (gray), H
À
is deprotonated into H PO4 anion; these two ionic species
2
are interacted via electrostatic interaction in the complex.
À
This protonation–deprotonation process yields H PO open
2
4
sites for facilitated proton transport. Moreover, these two
species further form two hydrogen-bonding interactions
(
white). c) N adsorption isotherm curves of TPB-DABI-COF (red
2
circles; filled: adsorption, open: desorption) and H PO @TPB-DABI-
between the N-H units of benzimidazole ring and the P=O
3
4
COF (blue circles; filled: adsorption, open: desorption).
À
bonds of H PO4 anion (Figure 1c).
2
Loading H PO into COFs and Characterizations. As the
3
4
pore volume reflects the space that is accessible to H PO , we
3
4
DABI-COF are summarized in the Supporting Information,
Table S1. The AA-stacking mode yields a PXRD pattern
used the pore volume of TPB-DABI-COF to determine the
maximum loading content of H PO in the pores. From the
3
4
À3
(
Figure 3a, green curve) which agrees well with the observed
density of neat H PO (1.834 gcm ) and the pore volume
3
4
3
À1
profile. In contrast, the AB-stacking mode (Figure 3a, purple
curve) cannot reproduce the PXRD data.
(1.06 cm g ) of TPB-DABI-COF, the maximum H PO
3 4
loading content is 66.1 wt%. Experimentally, we used neat
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H PO crystals and a vacuum impregnation method (Sup-
High-angle annular dark-field scanning TEM images
3
4
porting Information) to load into the channels of TPB-DABI-
confirmed a homogeneous distribution of C, N, O, and P
elements in H PO @TPB-DABI-COF (Figure S9). Thus,
[
7e]
COF and prepared H PO @TPB-DABI-COF. The result-
3
4
3
4
ing H PO @TPB-DABI-COF samples exhibited a negligible
H PO @TPB-DABI-COF enables spatial confinement and
3 4
3
4
porosity (Figure 3c, blue circles; Table S2), indicating that the
pores of TPB-DABI-COF are fully filled with H PO . FTIR
activation of the H PO network by the imine-linked poly-
benzimidazole walls.
3
4
3
4
spectroscopy confirmed the presence of H PO as evidenced
Impedance Studies and Anhydrous Proton Conduction.
We utilized impedance measurements to investigate the
conductivity of the pristine TPB-DABI-COF without instal-
lation of H PO by pressing the TPB-DABI-COF sample into
a round pellet under nitrogen. We observed that TPB-DABI-
COF itself is an insulator to show a resistance of 30 MW which
precludes any proton and/or electric conductivity (Figure S6).
Thus, TPB-DABI-COF is suitable as a proton-conducting
material.
3
4
by new stretching and in-plane bending vibration bands of the
À
À1
P=O bond of H PO4 anion at 980 and 498 cm , respectively
2
(
Figure S7). Noticeably, the vibration band of the C=N bond
shifted to 1649 cm (Figure S7), suggesting that the N atom
3
4
À1
of the C=N linkage forms hydrogen-bonding interaction with
[
7e]
H PO .
3
4
We further disclosed the interactions between H PO and
3
4
TPB-DABI-COF by using X-ray photoelectron spectroscopy
(
(
XPS). The high-resolution N 1s spectra of TPB-DABI-COF
Figure 4a) revealed two peaks at 399.45 and 400.35 eV,
We prepared pellets of H PO @TPB-DABI-COF by
3
4
pressing the H PO @TPB-DABI-COF samples under
3
4
which were assigned to the N atoms of the imine C=N bond
and of benzimidazole -C=N- bond, respectively.[ The high-
resolution N 1s spectra of H PO @TPB-DABI-COF showed
200 kN for 30 min under nitrogen and measured proton
conductivity by alternating-current impedance spectroscopy
under anhydrous condition under nitrogen. The Nyquist plots
of H PO @TPB-DABI-COF under anhydrous condition were
10]
3
4
that the benzimidazole -C=N- bond is shifted from 400.35 to
3
4
4
01.03 eV, reflecting the ionization of benzimidazole into
recorded by varying temperature from 100 to 1608C. The
intercepts on the Z’ axis was identified as the resistance. The
proton conductivity was calculated using the equation s =
L/SR, where s is the proton conductivity, L is the pellet
imidazolium cation, while the imine C=N bond is also shifted
to 401.03 eV, suggesting the hydrogen bonding interactions
with H PO (Figure 4b). The binding energies for C 1s spectra
3
4
2
of TPB-DABI-COF and H PO @TPB-DABI-COF are ob-
thickness (cm), S is the electrode area (cm ), and R is the
3
4
served at 284.9, 286.1, and 286.6 eV (Figure 4c,d). The first
and second peaks are attributed to the C=C and C=N bonds in
resistance (W). The proton conductivities were calculated to
be 7.37 ꢁ 10 , 8.59 ꢁ 10 , 9.71 ꢁ 10 , 1.09 ꢁ 10 , 1.22 ꢁ 10 ,
À2
À2
À2
À1
À1
À1
À1
À1
the COF skeleton. The peak at 286.6 eV (Figure 4d) was
assigned to the carbon atom bonded to charged nitrogen
1.39 ꢁ 10 , and 1.52 ꢁ 10 Scm at 100, 110, 120, 130, 140,
150, and 1608C, respectively (Figure 5a; Figure S10,
Table S5). Notably, these proton conductivities are even at
+
[11]
atoms (C=NH ). The P 2p XPS spectrum of H PO @TPB-
3
4
À1
À1 [12]
DABI-COF was deconvoluted into two peaks at 134.2 and
35.0 eV, which were assigned to the phosphorus atoms of
the same level of neat molten H PO ( ꢀ 10 Scm ).
3
4
1
Polybenzimidazole systems have a proton conductivity
that is one order of magnitude lower than that of neat H PO ,
À
[12,13]
H PO4 and H PO , respectively (Figure S8).
Together
2
3
4
3
4
with the single crystal structure, these analyses unambigu-
ously revealed multiple hierarchical interactions between
polybenzimidazole walls with the H PO networks.
as the swollen polymer chains exert steric hindrance to
impede proton motion, while the swollen chains leak H PO
3
4
[
2d,14,15]
and result in a low performance stability.
These bottle-
3
4
necks are associated with the structural features of poly-
benzimidazoles. In contrast, the proton conductivity of
H PO @TPB-DABI-COF is improved by 1–4 orders of
3
4
magnitude compared to other systems (Table S4). Among
metal-organic frameworks, the highest proton conductivity is
À3
À1
[16]
3
.0 ꢁ 10 Scm at 1508C observed for H PO @MIL-101.
3 4
The highest anhydrous proton conductivity of H PO @COFs
3
4
À1
À1
is
H PO @TPB-DMeTP-COF
(1.91 ꢁ 10 Scm
at
3
[
4
7e]
1
608C),
followed by H PO @TPB-Azo-COF (6.70 ꢁ
Scm at 678C; Tables S4 and S5).
The H PO @TPB-DMeTP-COF achieves an anhydrous
3
4
À5
À1
[6b]
1
0
3
4
À1
À1
proton conductivity of 1.91 ꢁ 10 Scm
at 1608C. The
exceptional proton conductivity of H PO @TPB-DABI-
3
4
COF is encouraging as H PO @TPB-DABI-COF has a far
3
4
much low H PO content of 66.1 wt%, which is one fourth
3
4
that of H PO @TPB-DMeTP-COF with a H PO content of
3
4
3
4
2
66.6 wt%. We tested the long-term stability of H PO @TPB-
3 4
DABI-COF at 1608C for 120 h and observed that the
proton conductivity retains the same value as its initial one
(Figure 5a, black curve; Figure S11). We plotted the proton
Figure 4. High-resolution XPS spectra of the a) N 1s band of TPB-
conductivity versus temperature to examine the temperature
dependency. As shown in Figure 5d (black curve), an
DABI-COF, b) N 1s band of H PO @TPB-DABI-COF, c) C 1s band of
3
4
TPB-DABI-CO, and d) C 1s band of H PO @TPB-DABI-COF.
3
4
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H PO content (Table S2). Surprisingly, the proton conduc-
3
4
À3
tivities of 42.9 wt% H PO @TPB-DABI-COF are 2.75 ꢁ 10 ,
.81 ꢁ 10 , 4.56 ꢁ 10 , 5.26 ꢁ 10 , 6.08 ꢁ 10 , 7.43 ꢁ 10 , and
.35 ꢁ 10 Scm at 100, 110, 120, 130, 140, 150, and 1608C,
3
4
À3
À3
À3
À3
À3
3
8
À3
À1
respectively (Figure 5c; Figure S17). Intriguingly, these pro-
ton conductivities are two-to-eleven-fold as high as than those
of amorphous H PO @TPB-DABI-POP under otherwise
3
4
same conditions.
These results indicate that the COF channels help to form
H PO networks and promote proton transport. More ex-
3
4
plicitly, H PO @TPB-DABI-POP exhibits an E value of
3
4
a
0
.61 eV (Figure 5d, blue curve), which is much higher than
that (0.23 eV) of 42.9 wt% H PO @TPB-DABI-COF (Fig-
3
4
ure 5d, red curve). The irregular pores of TPB-DABI-POP
unlike the 1D channels of TPB-DABI-COF, suppress an
efficient extension of hydrogen-bonding H PO network. The
3
4
irregular structure in H PO @TPB-DABI-POP leaves slug-
3
4
gish proton motion via a vehicle mechanism.
Figure 5. a) Nyquist plots of H PO @TPB-DABI-COF at 1008C (or-
3
4
ange), 1208C (green), 1408C (blue), 1608C (red) and 1608C after
a 120 h run (black). b) Nyquist plots of H PO @TPB-DABI-POP at
3
4
Conclusion
1
008C (orange), 1208C (green), 1408C (blue), and 1608C (red).
c) Nyquist plots of 42.9 wt% H PO @TPB-DABI-COF at 1008C
3
4
In summary, we have demonstrated a strategy for design-
ing polybenzimidazole COFs with inherent yet ordered 1D
pores to achieve ultrafast yet stable anhydrous proton
conduction over a wide range of temperatures above 1008C.
The porous polybenzimidazole frameworks are thermally and
chemically stable to enable the spatial confinement of
phosphoric acid in the pores. The channel walls trigger
multipoint, multichain, and multitype electrostatic and hydro-
gen-bonding interactions with phosphoric acid networks, so
that the proton-conducting systems are not only stabilized but
also activated via a protonation–deprotonation process. This
configuration not only offers ordered paths to achieve
ultrafast proton conduction at a low H PO content, but also
(
orange), 1208C (green), 1408C (blue), and 1608C (red). d) Arrhenius
plots of H PO @TPB-DABI-COF (black), 42.9 wt% H PO @TPB-DABI-
3
4
3
4
COF (red), and H PO @TPB-DABI-POP (blue).
3
4
Arrhenius-type linear curve is deduced. From the slope of the
curve, the activation energy was evaluated to be 0.17 eV. This
result suggests a hoping mechanism for the proton to trans-
port over the H PO network in the nanochannels. Notably,
3
4
this activation energy is lower than that (0.34 eV) of
H PO @TPB-DMeTP-COF and thus enables high-rate pro-
3
4
ton conduction over a wide range of temperature over 1008C.
3
4
Indeed, H PO @TPB-DABI-COF exhibits higher conductiv-
locks the network to enable stable performance at high
temperatures. The polybenzimidazole COFs enable the
combination of anhydrous proton conductivity, performance
stability, low proton carrier loading content, and low thermal
activation energy in one system—a set of attractive features
that are highly desired for proton transport. With these
distinct features, we envision that COFs offer a way to design
well-defined porous polybenzimidazole materials for proton
conduction and advanced energy conversion.
3
4
[7e]
ities than H PO @TPB-DMeTP-COF from 100 to 1308C.
3
4
These results suggest that H PO @TPB-DABI-COF is unique
3
4
as it combines ultrafast proton conductivity, high stability, low
proton carrier content, and low activation energy—a set of
attractive features that are highly desired to be combined in
one material.
Comparative and Control Studies. In order to demon-
strate the importance of being ordered porous structure, we
synthesized an amorphous version TPB-DABI-POP as a con-
trol, which is amorphous (Figures S12) and has a different
microscopic image from that of crystalline TPB-DABI-COF Acknowledgements
Figure S13). TPB-DABI-POP exhibited a BET surface area
(
2
À1
3
À1
of 275.01 m g and a pore volume of 0.41 cm g (Fig-
ures S14 and S15, Table S2). By using the same protocol,
We gratefully acknowledge financial support from the Na-
tional Natural Science Foundation of China (21805173,
21975049). D.J. acknowledges a MOE tier 1 grant (R-143-
000-A71-114) and NUS startup grant (R-143-000-A28-133).
TPB-DABI-POP was loaded with H PO4 to yield
3
H PO @TPB-DABI-POP that contains 42.9 wt% H PO .
3
4
3
4
H PO @TPB-DABI-POP exhibited proton conductivities of
3
4
À4
À4
À4
À3
À3
2
2
1
.38 ꢁ 10 , 4.00 ꢁ 10 , 6.87 ꢁ 10 , 1.15 ꢁ 10 , 1.78 ꢁ 10 ,
.70 ꢁ 10 , and 3.87 ꢁ 10 Scm at 100, 110, 120, 130, 140, Conflict of interest
50, and 1608C, respectively (Figure 5b; Figure S16,
À3
À3
À1
Table S5).
In order to compare with TPB-DABI-POP system, we
prepared 42.9 wt% H PO @TPB-DABI-COF with the same
The authors declare no conflict of interest.
3
4
&
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Angewandte
Research Articles
Chemie
Zhang, Z. Jiang, Y. Chen, S. Ma, P. Cheng, Z. Zhang, Angew.
Chem. Int. Ed. 2020, 59, 3678 – 3684; Angew. Chem. 2020, 132,
707 – 3713.
Keywords: anhydrous proton conduction ·
electrostatic interactions · hydrogen-bonding interactions ·
polybenzimidazoles
3
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Version of record online: && &&
,
&&&&
Angew. Chem. Int. Ed. 2021, 60, 2 – 8
ꢀ 2021 Wiley-VCH GmbH
www.angewandte.org
&&&&
These are not the final page numbers!

Angewandte
Research Articles
Chemie
Research Articles
Covalent Organic Frameworks
J. Li, J. Wang, Z. Wu, S. Tao,
Condensing benzimidazole units via
topology-directed polymerization allows
the construction of stable covalent
organic frameworks with ordered one-
dimensional channels. The walls trigger
multiple hierarchical interactions so that
the proton networks are locked in the
pores via spatial confinement and acti-
vated via deprotonation. Ultrafast and
stable anhydrous proton conduction is
achieved over a wide range of temper-
atures.
D. Jiang*
&&&& — &&&&
Ultrafast and Stable Proton Conduction in
Polybenzimidazole Covalent Organic
Frameworks via Confinement and
Activation
&
&&&
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ꢀ 2021 Wiley-VCH GmbH
Angew. Chem. Int. Ed. 2021, 60, 2 – 8
These are not the final page numbers!