MOF/PEDOT/HPMo-based polycomponent hierarchical hollow micro-vesicles for high performance flexible supercapacitors

Article abstract of DOI:10.1039/d0ta10603h

Metal-organic frameworks (MOFs) are promising electrode materials for supercapacitors; however, their electrochemical performances are limited by their low electrical conductivities. To address this problem, “conductive ink” poly(3,4-ethylenedioxythiophene) (PEDOT) was used to enhance the conductivity, while “electron sponge” polyoxometalate [PMo₁₂O₄₀]^3?(PMo₁₂) with large electronic transfer capability was used as the capacitance contributor. Finally, MOFs (PCN-224) acted as the host of this composite that provided the electrical double-layer capacitor and a PCN-224@PEDOT/PMo₁₂-CC-II hierarchical hollow micro-vesicle nanostructure was obtainedviaa simple one-step electro-codeposition. The microvesicle nanocomposite was interspersed in MOF hosts. Benefiting from the novel structure and the synergistic effect of three components, the optimal areal capacitance of the PCN-224@PEDOT/PMo₁₂-CC-II electrode was 4077.8 mF cm^?2at 5 mA cm^?2(the concentration ratio of EDOT?:?PMo₁₂is 1?:?0.75), which is 32.9 times more than that of pristine PCN-224 (123.6 mF cm^?2). Furthermore, a symmetric supercapacitor device was constructed by the PCN-224@PEDOT/PMo₁₂-CC-II nanocomposite, which possessed an excellent energy density of 0.297-0.0192 mW h cm^?2(at a power density of 0.324-5.128 W cm^?2) and a good long-term cycle ability (84.59% for 10?000 cycles at 5 mA cm^?2). This study presented a one-step electro-deposition synthetic strategy for the design and fabrication of the high-capacitance MOF-based electrode material, which showed great promise in the future design of high-performance materials for advanced energy production.

Full text of DOI:10.1039/d0ta10603h

Journal of
Materials Chemistry A
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MOF/PEDOT/HPMo-based polycomponent
hierarchical hollow micro-vesicles for high
performance flexible supercapacitors†
Cite this: J. Mater. Chem. A, 2021, 9,
948
2
a
a
a
a
a
ab
Bing Wang, Shuo Liu, Lin Liu,
Wen-Wei Song, Yue Zhang, Shi-Ming Wang*
a
and Zheng-Bo Han
*
Metal–organic frameworks (MOFs) are promising electrode materials for supercapacitors; however, their
electrochemical performances are limited by their low electrical conductivities. To address this problem,
“
“
conductive ink” poly(3,4-ethylenedioxythiophene) (PEDOT) was used to enhance the conductivity, while
3ꢀ
electron sponge” polyoxometalate [PMo12
O
40
]
(PMo12) with large electronic transfer capability was
used as the capacitance contributor. Finally, MOFs (PCN-224) acted as the host of this composite that
provided the electrical double-layer capacitor and a PCN-224@PEDOT/PMo12–CC-II hierarchical hollow
micro-vesicle nanostructure was obtained via a simple one-step electro-codeposition. The microvesicle
nanocomposite was interspersed in MOF hosts. Benefiting from the novel structure and the synergistic
effect of three components, the optimal areal capacitance of the PCN-224@PEDOT/PMo12–CC-II
ꢀ2
ꢀ2
electrode was 4077.8 mF cm
at 5 mA cm (the concentration ratio of EDOT : PMo12 is 1 : 0.75),
ꢀ2
which is 32.9 times more than that of pristine PCN-224 (123.6 mF cm ). Furthermore, a symmetric
supercapacitor device was constructed by the PCN-224@PEDOT/PMo12–CC-II nanocomposite, which
ꢀ2
possessed an excellent energy density of 0.297–0.0192 mW h cm (at a power density of 0.324–
Received 30th October 2020
Accepted 16th December 2020
ꢀ
2
ꢀ
2
5
.128 W cm ) and a good long-term cycle ability (84.59% for 10 000 cycles at 5 mA cm ). This study
presented a one-step electro-deposition synthetic strategy for the design and fabrication of the high-
capacitance MOF-based electrode material, which showed great promise in the future design of high-
performance materials for advanced energy production.
DOI: 10.1039/d0ta10603h
rsc.li/materials-a
materials for supercapacitors, which provide large electrolyte-
accessible surface areas and EDLC. Yaghi et al. explored
1
Introduction
6,7
Sustainable storage technologies aiming to resolve the energy various MOF-based electrode materials for supercapacitors with
and environmental crisis have been a worldwide research high capacitances; a zirconium MOF (nMOF-867) exhibited
8
target. Electrochemical capacitors, also known as super- exceptionally high capacitance. Samor `ı et al. reported MOF-
capacitors (SCs), with the merits of environmental benignity, UiO-66-NH as the substrate and obtained superior capacitor
2
fast charge/discharge capacities, excellent cycling lives, safety, performance aza-MOFs@COFs hybrid porous electrode mate-
and low cost, have triggered increasing attention as promising rials through the aza-Diels–Alder cycloaddition reaction with an
ꢀ
2
9
1–3
energy storage devices. Generally, there are three prerequi- areal capacitance of 20.35 mF cm . Huang et al. utilized the in
sites for SCs electrode materials, i.e., high electrochemical situ self-transformation method to prepare MnOx-MOF
energy storage abilities (electric double layer capacitance EDLC, manganese hexacyanoferrate hydrate (MHCF) nanocube-based
pseudocapacitance), large electrolyte-accessible surface areas, composite material with improved capacitor and rate perfor-
ꢀ
1
10
4
and high conductivity.
mance (1200 F g ). However, the poor conductivity of MOF-
Metal–organic frameworks (MOFs) are crystalline porous based composite materials hampered their wide application
materials constructed by linking metal-containing nodes with in capacitors. Contemporaneously, polyoxometalates (POMs),
5
organic ligands, which are considered as excellent electrode a kind of nanoscaled metal oxide clusters with diverse struc-
tures, are reputed as “electron sponges” with multi-electron
11–15
redox properties.
According to the literature, POM-based
a
College of Chemistry, Liaoning University, Shenyang 110036, P. R. China. E-mail:
composites have proved to be promising capacitor materials.
One disadvantage of most POMs is their good solubility in
various solvents, which makes them easy to dissolve and be lost
from the electrode. Combining soluble POMs with other
insoluble components is the most effective way to solve this
ceshzb@lnu.edu.cn
b
Light Industry College, Liaoning University, Shenyang 110036, P. R. China. E-mail:
wangsm@lnu.edu.cn
†
Electronic supplementary information (ESI) available. See DOI:
0.1039/d0ta10603h
1
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problem. However, similar to MOFs, POMs also suffer from low acid (H
3
PMo12
O40$nH
2
O), potassium hydroxide (KOH, $96%),
conductivity, which limits their performances as electrode 3,4-ethoxylene dioxythiophene (EDOT, $99%), N,N-dime-
materials. Some efforts have been made to enhance the thylformamide (DMF, $99%), tetrahydrofuran (THF, $99%),
16
conductivity of MOFs and POM-based electrode materials. For methanol (MeOH, $99%), and sulfuric acid (H SO , $98%)
2
4
example, Lan reported a novel polyoxometalate-based metal– were purchased from Sinopharm Chemical Reagent Co., Ltd.
organic framework (POMOFs)/reduced graphene oxide (rGO) Carbon cloth was purchased from CeTech.
nanocomposite for battery and supercapacitor. rGO lms can
improve the conductivity of composite materials and are thus
used as excellent supports to avoid the agglomeration of nano-
POMOFs particles. Wang et al. introduced MXene to prepare
Preparation of the PCN-224–CC precursor
In order to gra carboxyl and hydroxyl groups on the carbon
17
2
cloth (1 ꢁ 1.5 cm ), we activated it in the concentrated sulfuric
the Co-MOF/Ti C T @Ni composite material, which increased
3
2 x
acid and nitric acid mixture (VH
2
SO
4
: VHNO
3
¼ 3 : 1) for 4
the active sites and afforded a fast ion transport path while
4 2
hours. ZrCl (0.06 g), H TCPP (0.025 g), and benzoic acid (0.6 g)
in DMF (4 mL) were ultrasonically dissolved in an 18 mL Teon-
lined stainless-steel vessel and nally, carbon cloth was put into
ꢀ1
18
providing capacitance of 3741 F g
. The conductive polymer
poly(3,4-ethylenedioxythiophene) (PEDOT) with high electric
conductivity is oen applied in SCs to enhance the conductivity,
which can overcome the barrier of poor electric conductivity of
ꢂ
it. The vessel was sealed and heated at 120 C for 24 h under
autogenous pressure and then cooled to room temperature
naturally. Cubic dark purple crystals were grown on the carbon
cloth in situ, washed by DMF, and drying in vacuum overnight.
The mass loading of PCN-224 was calculated to be about
1
9–23
MOFs and POMs.
advantages of lightweight, safety, and foldability. Some of the
exible solid-state supercapacitors (SSCs) feature high stability,
exceptionally long cycle life, high power density, and low carbon
Flexible and wearable devices have the

ꢀ
2
1.85 mg cm
.
24–26
footprint.
Carbon cloth (CC) and ITO–PET, could be the
substrates for exible conductive electrodes. Therefore, we
27
Preparation of PCN-224@PEDOT/PMo12–CC-n
intent to use phosphomolybdic acid as the electron sponge,
PEDOT to enhance the conductivity, and MOFs with high Three pieces of PCN-224–CC as the working electrode was
specic surface area porous channels to construct the immersed in a three-electrode cell. The electrolytes contained
composites with hierarchical pores and high conductivity. At 0.08 M LiClO and different concentrations of EDOT : PMo in
4
12
the same time, CC was employed as the substrate to achieve the ratio of 1 : 0.25, 1 : 0.75, and 1 : 1.5, respectively. Then,
exible electrodes. electrodepositions were further carried out at a scan rate of

ꢀ
1
In this paper, we selected PCN-224, a kind of Zr-based MOF 50 mV s , cycling of the potential between ꢀ1 and 1 V with Ag/
with high stability, as the electrical charge storing material. AgCl as the reference electrode for 300 s, and Pt plate as the
Carbon cloth, a highly conductive textile, was used as both the counter electrode at the RT. The obtained PCN-224@PEDOT/
substrate and current collector with outstanding mechanical PMo12–CC-(I, II, III) was washed with distilled water several
28

exibility and strength. PCN-224 is in situ grown on the carbon times and vacuum-dried overnight.
cloth and linked by electrodeposited PEDOT/PMo . Finally, the
1
2
composite electrodes (PCN-224@PEDOT/PMo –CC-n) were
1
2
Fabrication of the exible supercapacitor device
obtained. In a three-electrode system, exceptional areal capac-
itance of 4077.8 mF cm at 5 mA cm for optimized PCN-
A PVA/H
in 10 mL 0.01 M H
the solution in air until it cooled down to room temperature.
Subsequently, two pieces of the PCN-224@PEDOT/PMo12–CC-II
2
SO
4
gel electrolyte was prepared by dissolving 1 g PVA
ꢀ2
ꢀ2
ꢂ
2
SO
4
aqueous solution at 85 C and leaving
2
2
24@PEDOT/PMo12–CC-II was achieved. Compared to PCN-
24–CC, PEDOT/PMo12–CC, and PCN-224/PEDOT–CC, the areal
capacitance showed 32.9, 2.7, and 2.0 times enhancement,
respectively. Moreover, a exible symmetric supercapacitor
device was constructed, which yielded a remarkable areal
2
electrodes (1 ꢁ 2 cm ) were chosen and each was half-immersed
into the prepared PVA/H SO gel electrolyte for 30 minutes;
2
4
then, the supercapacitor device was assembled by sandwiching
the PVA/H SO membrane between the two electrodes. In order
to avoid the occurrence of short circuits, the device was le
standing under infrared light for several hours for the complete
solidication of the electrolyte. The preparation of the PVA/
ꢀ
2
ꢀ3
capacitance of 218.5 mF cm (874 mF cm ). The high energy
ꢀ
2
2
4
densities of 0.0297–0.0192 mW h cm (0.132–0.0853 mW h
ꢀ
3
cm ) were achieved at the power densities of 0.324–5.128 W
ꢀ
2
ꢀ3
cm (1.358–21.934 W cm ). The superior capacitance reten-
ꢀ
2
tion (84.59% for 10 000 cycles at 5 mA cm ) indicates
outstanding cycling performance.
2 4
Na SO gel electrolyte is given in the ESI.†
Materials characterization
2
Experimental section
The structure of the as-prepared samples was characterized by
powder X-ray diffraction (PXRD) patterns that were recorded on
Materials
The commercial chemicals used in this study were commer- a Bruker AXS D8 advanced automated diffractometer at 40 kV and
˚
cially obtained without further purication and deionized water 30 mA with Cu Ka radiation (l ¼ 1.54060 A). The Raman spectra
was used in the process of experiments. Zirconium chloride were collected by a Renishaw confocal micro-Raman spectrometer
4
(ZrCl , $99%),4-carboxybenzaldehyde, benzoic acid ($99%), equipped with a 532 nm laser operated at 0.1% power. X-ray
propionic acid ($99%), pyrrole (Aldrich), phosphomolybdic photoelectron
spectroscopy
(XPS)
was
obtained
by
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monochromated X-rays (Quantum 2000, USA) using Al Ka radia- 224 was coated on the surface of the CC bres uniformly with
tion. Micromorphology and structural analysis were conducted the thickness of 0.5 mm via a facile solvothermal approach for
using a scanning electron microscope (Hitachi SU8010 (SEM) 48 h. Subsequently, PEDOT and PMo12 were weaved into the
system). EDS and elemental mapping patterns were acquired on surface and channels of the PCN-224 by the electrochemical co-
the SEM instrument (Oxford Instruments). Transmission electron deposition method. The isolated MOF crystals were inter-
microscopy (TEM) images were obtained on a JEM-2100 appa- connected and linked by the hollow micro-vesicles of PEDOT
ratus. The contact angle was measured on a Theta/Attension and PMo12, which acted as the bridges for electron trans-
Optical Tensiometer (SDA 100). The FT-IR spectra were recorded portation between the external circuit and the internal surface
on a Nicolet 5DX spectrometer using KBr pellets in the 4000– of the MOFs. As shown in Fig. 1b, the CC bres showed
ꢀ
1
4
00 cm range. The N adsorption–desorption isotherms were a smooth surface and the diameter of the bres was about 5 mm,
2
measured using a BeiShiDe 3H-2000PS1 system at 77 K.
and the raw CC had a black color (as shown in the inset of
Fig. 1b). Aer the solvothermal reaction, the black CC piece
turned brown red (inset in Fig. 1c) and the bres turned less
smooth compared to the CC bres, which evidenced that CC
was entirely enveloped by PCN-224 (Fig. 1c). Aer the co-
deposition of PEDOT/PMo12, the micro-vesicles covered the
surface of the bres and the roughness of the bre continued
growing, which indicated that PCN-224–CC were further wrap-
ped and weaved by the uniform hollow micro-vesicles (Fig. 1d).
Meanwhile, the color of the electrode switched to dark blue,
which originated from the color of PEDOT and reduced PMo12
Electrochemical characterization
The electrochemical behavior was investigated in a three-
electrode system in 1 M H SO aqueous electrolyte. The nano-
2
4
composite PCN-224@PEDOT/PMo –CC-II was used as a working
1
2
electrode, and Pt plate and Ag/AgCl electrode were used as the
counter and reference electrodes, respectively. Cyclic voltamme-
try (CV), galvanostatic charge–discharge (GCD) measurements,
and electrochemical impedance spectroscopy (EIS) were carried
out on a CHI660E electrochemical workstation at RT. The EIS
data were collected with an alternate current voltage of 5 mV
amplitude in the frequency range from 0.01 Hz to 100 kHz. The
test of GCD was carried out from 0 to 1 V at 5, 10, 15, and 20 mA
(inset of Fig. 1d). Finally, the hierarchical hollow micro-vesicle
nanocomposite PCN-224@PEDOT/PMo12–CC-II was assembled.
In order to evaluate the impact of the ratio of EDOT and
PMo12 in the depositing solution on the nanocomposites, the
concentration ratio of EDOT/PMo12 of 1 : 0.25 (I), 1 : 0.75 (II),
ꢀ2
cm . The methods applied for calculating the specic capacity,
specic capacitance, energy and power density symmetric
supercapacitor device is provided in the ESI.†
1
: 1.5 (III) in the solution for electrodeposition was used to
prepare the PCN-224@PEDOT/PMo –CC-n (n: I, II, III). As the
1
2
concentration of PMo12 increased, the macroscopic size of the
vesicles decreased from ꢃ3 mm to ꢃ1–2 mm and then increased
to ꢃ3–4 mm again. All the prepared nanocomposites were
employed for supercapacitors. According to the experimental
results, when the concentration ratio is 1 : 0.75 and the
3
Results and discussion
Morphology and structural characterization
The preparation route of the PCN-224@PEDOT/PMo –CC-II
1
2

exible electrode is briey illustrated in Fig. 1a. Firstly, PCN-
Fig. 1 (a) Scheme for the in situ growth of the PCN-224@PEDOT/PMo12–CC-II flexible electrode; (b) carbon cloth substrate; (c) hydrothermal
preparation of PCN-224–CC; (d) electrochemical co-deposition preparation of PCN-224@PEDOT/PMo12–CC-II.
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deposition time is 300 s, PCN-224@PEDOT/PMo12–CC-II the basis to form the hollow vesicles. (2) In turn, when the
exhibited the best electrochemical performance, possessing potential changed from ꢀ1 to +1 V, the positively charged
ꢀ
2
ꢀ2
+
an areal capacitance of 4077.8 mF cm at 5 mA cm . As the PEDOT (S ) would be adsorbed by the negatively charged PMo
1
2
control experiments, we also prepared PCN-224–CC (123.6 mF to form new positive surfaces. (3) Under the CV process, the
ꢀ
2
ꢀ2
cm ), PEDOT/PMo12–CC (1532.3 mF cm ), and PCN- surfaces grew alternately, leading to a hierarchical vesicle
ꢀ2
2
24@PEDOT–CC (1985.2 mF cm ) via the same method.
structure (Fig. 3); the corresponding opening hierarchical
Moreover, for the sake of exploring more structural infor- vesicle photo is shown in the inset in Fig. 2c. The advantage of
mation about PCN-224@PEDOT/PMo12–CC-n, further amplied this hierarchical vesicle is that PEDOT and PMo12 can be tightly
SEM and TEM images of this composite at different stages were woven on the pores and the surface of MOFs, which had the
recorded (Fig. 2c–f). The particle size of nano-crystalline PCN- dual effects of increasing the specic surface area of the elec-
224 in situ grown on CC was 150–300 nm (Fig. 2a and b). trode material and improving the conductivity of the material.
However, the surface of PCN-224@PEDOT/PMo –CC-II showed The ratio of EDOT and PMo12 in the deposition solution would
1
2
uniform “red blood cell”-shaped hollow vesicles, which were also be affected by the size and quality of the vesicles. Different
composed of dense nanocapsules (Fig. 2c and d). The changes ratios of EDOT : PMo12 were employed to examine the relation
in appearance also revealed that the PEDOT/PMo12 layer was between the concentration ratios of EDOT : PMo12 and the size
ꢀ
1
successfully coated on the surfaces of PCN-224. From the TEM of the vesicles. When the concentration of PMo12 is 0.4 g L
images of the sample, as shown in Fig. 2e and f, we can clearly and the EDOT : PMo12 mass ratio is 1 : 0.25, the vesicles for
see that the hollow vesicles were wrapped around PCN-224 and PCN-224@PEDOT/PMo –CC-I were incomplete; a defect state
1
2
present a hierarchical hollow morphology. According to the can be clearly seen in Fig. S1a.† When the concentration of
2
9
ꢀ1
literature and our experiments, PMo12 played an important PMo12 increased to 1.2 g L and the EDOT : PMo12 mass ratio
role for forming the hierarchical hollow micro-vesicle was 1 : 0.75, the vesicles of PCN-224@PEDOT/PMo12–CC-II
morphology. The formation mechanism could be attributed to appeared uniform, which are completely similar to the shape
the following aspects: (1) though the EDOT monomer and of red blood cells. If the concentration of PMo12 is continually
ꢀ
1
PMo12 were evenly dispersed in the solution for deposition, increased to 2.0 g L and the EDOT : PMo12 mass ratio is
PMo12 and PEDOT did not enter PCN-224–CC at the same time 1 : 1.5, a large amount of amorphous PEDOT mixed with PMo12
during the electrodeposition process. When the potential was deposited and agglomerated on the surface of PCN-224 to
changed from +1 to ꢀ1 V, PMo moved to the surface and form PCN-224@PEDOT/PMo –CC-III with large cavities
1
2
12
penetrated to the pores of PCN-224–CC to accept electrons. As (Fig. S1c†). The corresponding TEM images are shown in
a result, the matrix exhibited a negatively charged surface. Fig. S1b and d.† It can be attributed to the polyoxometalate
Actually, the negative charges were not continuous distributed agglomerates and the local concentration was higher than that
on the surface but isolated by the PMo12 nano-cluster. This was at other places, causing PEDOT to polymerize rapidly and form
Fig. 2 (a and b) SEM image of PCN-224–CC; (c and d) SEM image of PCN-224@PEDOT/PMo12–CC-II with different magnifications, respec-
tively; inset: the open hierarchical hollow micro-vesicles; (e and f) TEM images of PCN-224@PEDOT/PMo12–CC-II; (g-(1–8)) EDS mapping for
PCN-224@PEDOT/PMo12–CC-II.
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PCN-224@PEDOT/PMo12–CC-II displayed similar diffraction
conguration as that of PCN-224 with decreased peak intensity,
which indicated the successful enveloping of PEDOT/PMo . It
1
2
is worth mentioning that no diffractive peaks for PEDOT were
detected due to its amorphous nature, which matched well with
the HRTEM results (Fig. S2†).
The FTIR spectra of PMo12, PCN-224@PEDOT/PMo12–CC-II,
3 40
and PEDOT–CC are shown in Fig. 4b. Typical H [PMo12O ]
peaks were exhibited, conrming that PCN-224 and PMo12 are
assembled together. The characteristic bands of PMo are 798,
1
2
ꢀ
1
8
76, 979, and 1068 cm , which were ascribed to the stretching
vibrations of Mo–O –Mo, Mo–O –Mo, Mo–O , and P–O ,
d
c
d
a
respectively, were matched with that of PCN-224@PEDOT/
ꢀ1
Fig. 3 Schematic representation of the PEDOT/PMo12 micro-vesicle PMo12–CC-II (800, 843, 981, and 1084 cm ) with some
3
0–32
formation mechanism.
shis.
The results indicated that HPMo12 was successfully
33
loaded. Raman spectroscopy was performed to further
understand the chemical composition of PCN-224@PEDOT/
large cavities. To further understand the elemental dispersion PMo12–CC-II (Fig. 4c). The two intense peaks observed at 1423
ꢀ
1
in PCN-224@PEDOT/PMo –CC-II, EDS analysis was carried and 1509 cm were attributed to the symmetric and asym-
1
2
34
out. Uniform distribution of C, N, Zr, O, P, Mo, and S elements metric C]C stretching of PEDOT, respectively. In addition,
was observed, suggesting the homogeneous dispersion of PCN- small shoulders located at 1367 and 1563 cm were assigned to
ꢀ
1
2
24, PEDOT, and PMo12 on CC (Fig. 2g).
the overlaying between D and G bands of carbon cloth and the
The composition of PCN-224@PEDOT/PMo12–CC-II was strong Raman peaks of PEDOT.
35
examined by powder X-ray diffraction (PXRD) (Fig. 4a). Obvi-
ously, the PXRD patterns of the as-synthesized samples PCN- to investigate the surface area and pore size distribution of the
24–CC and PCN-224@PEDOT/PMo –CC-II matched well with samples. The BET surface areas of PCN-224, PCN-224–CC, and
Nitrogen adsorption measurements at 77 K were conducted
2
1
2
their simulated patterns, thus demonstrating their phase PCN-224@PEDOT/PMo12–CC-II were calculated to be 1628.5,
ꢂ
ꢂ
2
ꢀ1
purities. The two appeared peaks located at 26 and 44 are 226.8, and 102.7 m
g , respectively, which indicated the
derived from the CC substrate (JCPDS no. 26-1076). As expected, permanent porosity characteristic of PCN-224@PEDOT/PMo12
–
Fig. 4 (a) XRD patterns of the PCN-224–CC (green), PEDOT/PMo12–CC (yellow), PCN-224@PEDOT/PMo12–CC-II (purple), and activated CC
blue); (b) FTIR spectra of PCN-224@PEDOT/PMo12–CC-II, PMo12 and PEDOT–CC (purple, yellow, blue); (c) Raman shifts of PCN-224@PEDOT/
PMo12–CC-II; (d) N adsorption–desorption isotherms for the samples (PCN-224, blue; PCN-224–CC, green; PCN-224@PEDOT/PMo12–CC-II,
(
2
purple); (e) pore size distribution for the PCN-224, PCN-224–CC and of PCN-224@PEDOT/PMo12–CC-II (blue, green, purple); (f) Zr 3d high-
revolution spectra of PCN-224@PEDOT/PMo12–CC-II (i) and PCN-224–CC (ii).
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CC-II even aer co-electrodeposition (Fig. 4d). The pore size Electrochemical performance
distributions were investigated by non-local density functional
The electrochemical performances of the electrode materials
theory method; the results showed that the amount of the
micropores in PCN-224 were signicantly decreased and the
pore size generated by the space between the MOF particles was
also reduced (Fig. 4e). The decrease in the pore size and surface
area indicated that PEDOT and PMo12 covered the open spaces
between the particles as well as the internal micropores, which
allowed the electron to access the internal surface of PCN-224.
More importantly, though the pores in PCN-224 were partially
blocked by PEDOT and PMo , the electrolyte could still enter
were rstly studied by cyclic voltammetry (CV) in a three-
ꢀ1
electrode system using H
2
SO
4
solution (1 mol L ) as the elec-
trolyte from ꢀ0.2 to 0.8 V (vs. Ag/AgCl) at different scan rates. At
ꢀ1
the same scan rate of 10 mV s , different areas were reected
by the CV curves of different electrode materials. To investigate
the functions of each component in the composite lm, PCN-
224–CC, PCN-224@PMo –CC, PEDOT/PMo –CC, PCN-
12 12
2
24@PEDOT–CC, PCN-224@PEDOT/PMo –CC-I, II, and III
1
2
1
2
ꢀ1
electrodes were examined at the scan rate of 10 mV s
Fig. S5†). The capacity of the electrode was reected by the area
the pores via diffusion, which was detected by further electrical
performance evaluation. Furthermore, PCN-224 belongs to
microporous crystalline materials as it has 2.4 nm size pores
(
of the CV curves. PCN-224@PEDOT/PMo12–CC-II exhibited the
largest area among the electrodes, which showed 2.02 times
larger area than the area sum of PCN-224@PMo12–CC and PCN-
36
due to the defects of MOFs. These results revealed that PEDOT
and PMo12-engineered PCN-224 retained the vesicle structure
with large, open MOF areas, which may provide more active
sites on the surface to contact with the electrolyte and shorten
2
2
24@PEDOT–CC. For activated PCN-224–CC and PCN-
24@PMo –CC, the CV areas were negligible. Aer introducing
1
2
conductive PEDOT, the two-component electrode materials
PEDOT/PMo12–CC and PCN-224@PEDOT–CC) were still not
37
the electron transfer pathways. In addition, the inter-
connected network architecture enabled to increase the
(
ideal as the area was still smaller than the ternary component
38
mechanical stability during the charge and discharge process.
PCN-224@PEDOT/PMo12–CC-n. The areal capacitance of PCN-
The PXRD, Raman, FTIR, and nitrogen adsorption measure-
ment results indicated the successful enveloping of PEDOT and
PMo12 around the surface and the inside of PCN-224
successfully.
ꢀ2
2
24@PEDOT/PMo12–CC-II was 2218.6 mF cm , which is 19.6
times that of PCN-224–CCand surpassed that of PCN-
ꢀ2
ꢀ1
2
24@PEDOT–CC (947.2 mF cm at 10 mV s ) by 223%, thus
indicating the enhanced capacitance from the EDLC due to the
high surface area and porosity of PCN-224 and the pseudoca-
X-ray photoelectron spectroscopy (XPS) was further per-
formed to investigate the chemical compositions and valence
states. With regard to PCN-224@PEDOT/PMo –CC-II, the
pacitance of PEDOT/PMo12. The areal mass loading of PCN-
1
2
ꢀ2
2
24@PEDOT/PMo12–CC-II was about 6.2 mg cm (the mass
elements Zr, C, O, N, S, P, and Mo were detected in the full
survey spectrum (Fig. S3a†). Five deconvoluted peaks (284.5,
ratio of PEDOT/PMo12 is 1/0.75) and the thickness of PCN-
24@PEDOT/PMo12-II was about 1.5–2 mm, as shown in
Fig. S6.† The corresponding specic capacitance for PCN-
2
286.2, 287.2, 287.8, and 290.1 eV) were obtained from the C 1s
spectrum of PCN-224@PEDOT/PMo12–CC-II (Fig. S3b†), which
were correspondingly assigned to C–C (C–S), C]C–O, C–O–C,
C]O, and O–C]O, respectively. However, the corresponding
peaks of PCN-224–CC (Fig. S4a†) shied to lower binding energy
area, which conrmed the successful deposition of PEDOT and
the successful deposition of PEDOT. The high-resolution Mo 3d
ꢀ1
ꢀ1
2
24@PEDOT/PMo –CC-II was 518.6 F g at 10 mV s .
12
The CV curve of PCN-224@PEDOT/PMo –CC-II exhibited
1
2
a mirror-image current response and the presence of redox
reaction peaks, which indicated the coexistence of both the
EDLC behavior and pseudocapacitance (Fig. S5†). More
importantly, this three-component composite exhibited higher
enclosed CV curve area and a higher redox peak intensity
compared to the two-component and single-component ones,
which revealed a signicant improvement of the capacitance
and faster redox reaction kinetics processes. The areal capaci-
VI
spectrum exhibited two different valence states, namely, Mo
IV
and Mo (Fig. S3d†). The acquired spectra demonstrate that
both the Zr 3d and O 1s orbitals were electronically perturbed
upon the incorporation of PEDOT/PMo12 into the PCN-224
structure. In Fig. 4f, a positive shiing of the Zr 3d5/2 orbital
from 182.4 eV (PCN-224–CC) to 182.7 eV (PCN-224@PEDOT/
PMo –CC-II) suggested that the Zr node in PCN-224 binds to
ꢀ1
ꢀ2
tances at 10 mV s were only 113.2 mF cm for PCN-224–CC,
ꢀ2
ꢀ2
1
53.8 mF cm for PCN-224@PMo12–CC, 647.4 mF cm for
PEDOT/PMo12–CC, and 947.2 mF cm for PCN-224@PEDOT–
CC, which increased signicantly to 2218.6 mF cm for PCN-
1
2
ꢀ2
the moiety of PEDOT/PMo12, which can attribute to the defect
sites in the synthesized MOFs, which is consistent with the pore
size distribution results (Fig. 4e). As expected, the binding
energy of O 1s (Fig. S3c†) also showed a positive shi (0.79 eV)
compared to PCN-224 (Fig. S4b†), which agrees well with the
result mentioned above. Comparing PCN-224@PEDOT/PMo –
ꢀ2
224@PEDOT/PMo12–CC-II; this is possibly due to the hierar-
chical hollow micro-vesicles structure with uniform
morphology, which can provide a larger electrolyte contact area,
thereby promoting electron transfer and ion diffusion. PCN-
1
2
2
1
24@PEDOT/PMo –CC-I and III gave areal capacitances of
12
402.6 and 1526.7 mF cm because the hierarchical vesicles
CC-II with PCN-224–CC, N 1s spectrum shied to higher
binding energy, as shown in Fig. S3e and S4c.† The high-
resolution S 2p and P 2p spectra are shown in Fig. S3f and g.†
These observations clearly indicated the re-establishment of the
electronic structure of the PCN-224@PEDOT/PMo12–CC-II
composite, which would benet the pseudocapacitive
ꢀ2
were incomplete under the low concentration of PMo12; thus,
the electron transport was blocked. When using a higher
concentration of PMo12, the progress of the electrochemical
reactions was weakened by the agglomerated vesicles and
increased cavity (Fig. S1†). Three redox peaks were detected at
39
behavior.
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ꢀ
0.01, 0.31, and 0.55 V, which could be attributed to the 3-step be claried. Therefore, the CV curves of PCN-224@PEDOT/
40
redox processes of PMo (eqn (1)–(3)).
PMo –CC-n at different scan rates ranging from 10 to 100 mV
12
1
2
ꢀ
1
s
were collected (Fig. 5a and S7†). The CV current densities of
3
ꢀ
ꢀ
+
403ꢀ
O
PMo12
PMo12
H PMo O
O
40 + 2e + 2H # H
2
PMo12
403ꢀ
40 + 2e + 2H # H PMo12O
(1)
(2)
(3)
(4)
PCN-224@PEDOT/PMo –CC-II increased linearly with the
1
2
increase in the scanning rates, which indicated good electro-
3
ꢀ
ꢀ
+
H
2
O
4
42
chemical reversibility. The presence of three redox reaction
peaks corresponded to the successive redox reactions process of
the PMo12 cluster, accompanied by the reaction process of
PEDOT with the anions in the electrolyte while providing
pseudocapacitance. The CV of PCN-224@PEDOT/PMo –CC-I
3
ꢀ
ꢀ
+
403ꢀ
+ 2e + 2H # H PMo O
4
12 40
6
12
2
4
ꢀ
X+
) # (PEDOT )(SO
42ꢀ
ꢀ
+ Xe
X(PEDOT) + X(SO
)
x
1
2
ꢀ
1
and III at the scan rates of 10, 20, 50, and 100 mV s are
collected in Fig. S7a and b; † the decrease of the CV areas
indicated that the performances of the corresponding electrode
materials were lower than that of PCN-224@PEDOT/PMo12–CC-
II, and the maximum areal capacitances of 1402.6 and 1526.7
Obviously, compared with the other binary component elec-
trodes, the capacitance of PCN-224@PEDOT/PMo –CC-II
1
2
ꢀ
2
(2218.6 mF cm ) was far larger than the sum of the capaci-
ꢀ2
tance of PCN-224@PMo12–CC (153.8 mF cm ) and PCN-
ꢀ2
224@PEDOT–CC (947.2 mF cm ), which conrmed that PMo12
ꢀ
2
mF cm for PCN-224@PEDOT/PMo12-I/III electrode materials
and PEDOT synergize with each other to promote electron
transfer and that the ternary components were indispensable. In
the composite, the MOFs provided a large specic surface area,
PMo12 could promote electron transfer, and PEODT could
increase the conductivity of the material as the conductivity of
ꢀ
1
was obtained at the same scan rate of 10 mV s (Fig. S8†). The
experimental results meant there were two functions of PMo12
in the composite materials. The rst function was to adjust the
morphology by changing the concentration. When the
concentration of PMo12 was 0.4 g L , defects were detected in
ꢀ
1
ꢀ1
the electrode material containing PEDOT is 980 S cm , as
measured by the Four Probe Tester at room temperature, which
the vesicles (Fig. S1a and b†), which resulted in a discontinuous
41
12
electronic transfer path; when the concentrations of PMo was
was similar to that of pure PEDOT. The ratio of PEDOT/PMo12
also affected the morphology, thereby affecting the performance.
As discussed above, different ratios of EDOT and PMo12 in
the solution for electrodepositing would result in different
morphologies of the composites. Furthermore, how the
morphology affects the electrochemical performances should
ꢀ
1
increased to 2.0 g L , agglomerated vesicles and increased
cavities (Fig. S1c and d†) weakened the progress of the elec-
trochemical reactions, leading to a decrease in the capacitance.
The second function was to effectively promote electron transfer
and improve the capacitance performance.
ꢀ1
Fig. 5 (a) Electrode cyclic voltammograms of PCN-224@PEDOT/PMo12–CC-II under the scan rate of 10–100 mV s in a three-electrode
system and (b) the relation of the concentration ratio effect on the areal capacitance at different vesicle sizes. (c) Galvanostatic charge/discharge
curves of the PCN-224@PEDOT/PMo12–CC-II electrode at different current densities in 1 M H
yellow), PCN-224@PEDOT–CC (blue), PEDOT/PMo12–CC (green), and PCN-224@PEDOT/PMo12–CC-II (purple) at different current densities in
the three-electrode system configuration using H SO as the electrolyte. (e) Nyquist electrochemical impedance spectra of PCN-224–CC (red-
2 4
SO . (d) The areal capacitance of PCN-224–CC
(
2
4
brown), PEDOT/Mo12–CC (green), PCN-224@PEDOT–CC (blue), and PCN-224@PEDOT/PMo12–CC-II (purple). (f) Schematic representation of
electron and electrolyte conduction in PCN-224@PEDOT/PMo12–CC-II, PCN-224, and PMo12 interwoven by PEDOT.
2954 | J. Mater. Chem. A, 2021, 9, 2948–2958
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Thence, the concentrations of PMo12 and ratio of PEDOT/
Journal of Materials Chemistry A
It can be seen in Fig. 5d that a more superior capacitance
PMo12 were critical for the areal capacitance, which was mainly retention rate of 82.95% than that of PCN-224@PEDOT–CC
because the concentration of PMo12 directly affected the change (56.3%) and PEDOT/PMo –CC (45.56%) was obtained from 5 to
12
ꢀ2
in the materials' morphology. When the appearance and size of 20 mA cm , which might be because hydrophilic PEDOT and
the multilayer vesicles were relatively uniform, the concentra- PMo12 were weaved and inserted into the pores of PCN-224,
ꢀ
1
tion of the PMo12 vesicles was 1.2 g L and the areal capaci- which were accessible to the electrolyte and efficiently
ꢀ2
tance value was 2218.6 mF cm . With the increase in the PMo12 reduced the ‘dead’ mass in the electrode. The maximum areal
concentration, the vesicles did not show the expected gradual capacitances of the samples were obtained at the same current
ꢀ
2
trend but displayed a form of extreme change, from large to density of 5 mA cm , as shown in Table S1†. The contact angle
ꢂ
small and then returned to the large size again. The best of PCN-224@PEDOT/PMo –CC-II was close to 0 in contrast to
1
2
ꢂ
44
concentration ratio of EDOT : PMo12 was 1 : 0.75; the composite PCN-224–CC (ꢃ140.1 ) (Fig. S10†). From the SEM/TEM images
presented uniform multi-layered vesicles of 0.8–1 mm, while the and the XRD patterns of PCN-224@PEDOT/PMo –CC-II before
1
2
other concentrations showed damage and agglomeration in the and aer the charge–discharge process, it can be concluded that
vesicles, which could explain why PCN-224@PEDOT/PMo12–CC- the hierarchical micro-vesicles structures and the phase can still
II showed maximum capacitance (Fig. 5b).
be maintained (Fig. S11†), and PCN-224@PEDOT/PMo12–CC-II
The aforementioned experimental results showed that the has excellent cyclic stability.
appropriate surface areas and porosities, as well as good
The comparisons of the Nyquist plots of the four electrodes
conductivities, facilitated electron or ion transport, resulted in the revealed the origins of sizable capacitance (Fig. 5e) compared to
improvement of the electrochemical performance. This phenom- PCN-224–CC, PCN-224@PEDOT–CC, PEDOT/PMo –CC, and
1
2
enon indicated that the components and microstructures had PCN-224@PEDOT/PMo –CC-I–III electrodes; the hierarchical
1
2
a great inuence on the performance of the electrode materials. In micro-vesicles PCN-224@PEDOT/PMo12–CC-II demonstrated
addition, the areal capacitance of the sample electrode materials the lowest equivalent series resistance (1.31 U in the high
(PCN-224–CC, PCN-224@PMo12–CC, PCN-224@PEDOT–CC, frequency region), which conrmed that this wonderful struc-
PEDOT/PMo12–CC, and PCN-224@PEDOT/PMo12–CC-n) under ture of PCN-224@PEDOT/PMo12–CC-II can accelerate the
different current densities were also investigated by galvanostatic transport and diffusion of ions and electrons, accelerate charge
charge–discharge (GCD). The GCD curves were slightly distorted transfer kinetics, and thus contribute to the boosting of the
from the ideal triangular shape (Fig. 5c) because of the pseudo- pseudocapacitance. In addition, the straight line of the PCN-
43
capacitive contribution from PEDOT/PMo . Similar to the CV 224@PEDOT/PMo –CC-II low frequency region was nearly
12
12
curves, the PCN-224@PEDOT/PMo12–CC-II still revealed the parallel to the imaginary axis, further demonstrating the ideal
45,46
longest discharge time and showed an areal capacitance of 4077.8 capacitive performance.
The equivalent circuit of PCN-
mF cm at a current density of 5 mA cm . In contrast, the 224@PEDOT/PMo12–CC-II is shown in the inset of Fig. 5e.
capacity of PCN-224–CC, PCN-224@PMo12–CC, PEDOT/PMo12 Compared with the reported nanocomposite-based electrode
ꢀ2
ꢀ2
–
CC, PCN-224@PEDOT–CC, PCN-224@PEDOT/PMo12–CC-I and III materials in Table 1, the PCN-224 @ PEDOT/PMo12–CC-II
only gave an areal capacitance of 123.6, 395.1, 1532.3, 1985.2, composite material had higher performance, which can be
ꢀ
2
2402.6, and 2726.7 mF cm
at the same current density, attributed to the following reasons: (i) hierarchical hollow
respectively (Fig. S9†). As far as we know, this value was higher micro-vesicles structure can effectively adapt to the volumetric
than those of other MOF-based and polymer composite materials; change caused by the electrochemical reaction process, thus
the capacitance of PCN-224@PEDOT/PMo12–CC-II was about 2 improving the stability of the electrode materials. More
times larger than the best reported MOF-based electrode material importantly, it can provide effective diffusion channels for the
ꢀ
2
PANI–ZIF-67–CC (2146 mF cm ), as shown in Table 1.
electrolyte, thus efficiently reducing the dead mass of the
Table 1 Comparison of PCN-224@PEDOT/PMo12–CC-II with other MOF-based and polymer composite electrode materials
Scan rate/current
density
Capacitance
ꢀ2
Type
Morphology
Electrolyte
3 M KCl
(mF cm
)
Ref.
a,b
ꢀ2
NENU-5/PPy-0.15
PANI/CNTs/G/PETC
PANI–ZIF-67–CC
ZIF-67–PPy-2
PEDOT–GO/U–C
PEDOT/H-15G-CNTF
NENU-5/PPy/60
PCN-224@PEDOT/PMo12–CC-I
Nanoparticle
CNTs
Nanoparticle
Network
Curly fold
Porosity
Nanoparticle
Breakage of hollow micro-vesicles
Hierarchical hollow micro-vesicles
Agglomeration hollow micro-vesicles
Hierarchical hollow micro-vesicles
0.5 mA cm
1090
791
2146
2330
102
128
2034.5
2402.6
4077.8
2726.7
3636.3
54
55
48
51
47
53
56
a,b
ꢀ2
1 M H
3 M KCl
1 M Na
2
SO
4
1.5 mA cm
a,b
ꢀ1
10 mV s
a,b
ꢀ2
2
SO
4
10 mA cm
a,b
ꢀ1
1 M KCl
3 M KCl
10 mV s
a,b
ꢀ1
10 mV s
a,c
ꢀ2
ꢀ2
ꢀ2
ꢀ2
1 M H
1 M H
1 M H
1 M H
2
2
2
2
SO
4
4
4
4
20 mA cm
5 mA cm
5 mA cm
5 mA cm
a,b
SO
SO
SO
This work
This work
This work
This work
a,b
PCN-224@PEDOT/PMo12–CC-II
PCN-224@PEDOT/PMo12–CC-III
PCN-224@PEDOT/PMo12–CC-II
a,b
a,b
ꢀ2
1 M Na
2
SO
4
5 mA cm
a
b
c
In three electrode system. Flexible electrode material. Rigid electrode material.
This journal is © The Royal Society of Chemistry 2021
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Journal of Materials Chemistry A
Paper
electrode materials. (ii) Super stable PCN-224 with rich access effects, the synergy between PCN-224, PEDOT, and PMo12 can
channels. Moreover, the micropores not only cause the uniform establish an effective electron transfer path. The unhindered
dispersion of PMo12 and prevent PMo12 from dissolving in the electron transfer path is shown in the energy level diagram
electrolyte but also act as an electrochemical double layer (Fig. 6). During the discharge process, electrons owed from
capacitor, which favors charge storage/transport and the ionic PMo12 through PEDOT to PCN-224 with the lowest CB energy
diffusion. PMo12 inside the framework took part in the redox level and the discharge process was completed smoothly. The
reactions and provided pseudocapacitance because of the charging process was reversed. This facile electron transfer
VI
IV
transformation of Mo to Mo , which was conrmed by the helped to maximize the capacitance.
XPS results (Fig. S3d†). PEDOT can improve the conductivity of
the materials greatly and promote electron transfer. In addition, Device assembly and capacitance evaluation
the structure of PCN-224@PEDOT/PMo –CC-II was stable; the
1
2
To demonstrate the potential application of PCN-224@PEDOT/
unique structure facilitates electron storage and transmission
and ion diffusion. The schematic diagram of the mechanism is
shown in Fig. 5f. (iii) Beneting from the p–p conjugations
PMo12–CC-II in supercapacitors, we fabricated a symmetric all-
solid-state supercapacitor device. The same two pieces of PCN-
2
2
24@PEDOT/PMo12–CC-II electrodes with an area of 1 ꢁ 2 cm
were parallelly placed and PVA/H SO
2
4
gel was used as the sepa-
rator and the solid electrolyte (Fig. 7a). The effective area of the
2
device was approximately 2.0 cm . Its electrochemical behaviors
were studied using CV in the potential range from 0 to 1.0 V with
ꢀ
1
different scan rates from 5 to 50 mV s , which exhibited a large
closed area (Fig. S12a†). To further evaluate its electrochemical
performance, GCD measurements at relatively high current
ꢀ
2
densities from 0.5 to 5 mA cm were carried out (Fig. 7b). With
the increase in the current density, this solid device showed
decreased capacitance. The areal capacitances of this device were
ꢀ
2
2
15.7–143.8 mF cm at different current densities from 0.5 to 5
ꢀ2
mA cm . The high energy densities of 0.0297–0.0192 mW h
cm (0.132–0.0853 mW h cm ) were achieved at the power
densities of 0.324–5.128 W cm (1.358–21.934 W cm ), which
ꢀ2
ꢀ3
ꢀ
2
ꢀ3
Fig. 6 Energy level diagram of PCN-224, PEDOT, and PMo12
.
revealed that the device had potential applications in energy
Fig. 7 (a) Schematic representation of the PCN-224@PEDOT/PMo12–CC-II flexible SSC; (b) GCD curves of the device at the current density of
ꢀ
2
0
.5–5 mA cm ; (c) Ragone plots of the assembled PCN-224@PEDOT/PMo12–CC-II device and the comparisons of data covered by the
47–53
literature;
(d) cycling test via the GCD cycling process for 10 000 cycles (inset, an LED lit by the three devices); (e) the capacitance retention
after bending the solid-state supercapacitor 500 times. The inset shows the digital photos and CV curves at different bending stages; (f)
photographs of the three connected devices in series starting up one minifan.
2956 | J. Mater. Chem. A, 2021, 9, 2948–2958
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Journal of Materials Chemistry A
storage. The relationships between energy densities and power was constructed via simple electrodeposition. The unique hierar-
densities under various current densities are given in the Ragone chical vesicle structure can accommodate the volume change of the
plots (Fig. 7c). The performance of this device exceeds the values electrode materials and offers an efficient way for electronic
4
7–53
achieved for other reported MOF-based supercapacitors.
More importantly, superior capacitance retention (84.59% for frameworks vastly accelerated electron transfer and promoted the
1
transmission. The introduction of PMo12 into the PCN-224
ꢀ
2
0 000 cycles at 5 mA cm ) indicates the outstanding cycling kinetics of electrochemical reaction. PEDOT had high conductivity
performance (Fig. 7d).
and mechanical strength, which were benecial for the fabrication
When the neutral electrolyte Na
2
SO
4
was selected, the CV of high-performance exible SCCs. Indeed, electrons owed from
curves (three-electrode system) of PCN-224@PEDOT/PMo12–CC- PMo12 with a higher energy level through PEDOT to PCN-224 with
ꢀ
1
II in 1 mol L Na SO electrolytes at different scan rates (10– the lowest CB energy level. Because of the facile electron transfer in
2
4
ꢀ
1
1
00 mV s ) were recorded and are given in Fig. S13a.† The CV the composite, PCN-224@PEDOT/PMo –CC-II showed state-of-
current densities linearly increased, which conrms again that the-art capacitance of about 4077.8 mF cm , which is 32.9 times
PCN-224@PEDOT/PMo12–CC-II has good electrochemical larger than that of pristine PCN-224 (123.6 mF cm ) and the other
reversibility. Similar to acidic electrolyte systems, the GCD reported MOF-based supercapacitor. Meanwhile, the symmetric
curves were slightly distorted from the ideal triangle shape supercapacitor device based on PCN-224@PEDOT/PMo12–CC-II
12
ꢀ
2
ꢀ
2
(
Fig. S13b†) because of the pseudocapacitive contribution from was successfully developed, which exhibited an areal capacitance
ꢀ
2
PEDOT/PMo12. The maximum area capacitance of PCN- of 215.8 mF cm and which was far above that of other MOF-
2
density of 5 mA cm (Fig. S13c†), which still showed higher prepare MOF-based supercapacitor electrode materials and to
areal capacitance compared to the literature shown in Table 1. extend the diversity of the supercapacitor family.
We also assembled a symmetric exible supercapacitor device
ꢀ
2
24@PEDOT/PMO –CC-II is 3636.3 mF cm
at a current based supercapacitors. This work provides a new strategy to
1
2
ꢀ
2
with PCN-224@PEDOT/PMo12–CC-II and PVA/Na
trolytes between the electrodes. The CV curves of the device had
a large closed area and near rectangular shape at a scan rate of 5 There are no conicts to declare.
2 4
SO gel elec-
Conflicts of interest
ꢀ1
to 50 mV s (Fig. S14a†). The GCD curves of this device are
shown in Fig. S14b.† Based on the GCD curves at 0.5–5 mA
Acknowledgements
ꢀ
2
cm , the device exhibited an areal capacitance of 206.8–126.3
ꢀ2
mF cm . The high energy densities of 0.0288–0.0164 mW h We thank the National Natural Science Foundation of China
ꢀ
2
ꢀ3
cm (0.125–0.0753 mW h cm ) were achieved at the power (21501084, 21671090 and 21701076), Liaoning Revitalization
ꢀ2
ꢀ3
densities of 0.311–4.853 W cm (1.302–19.156 W cm ).
Talents Program (XLYC1802125), and Scientic Research
The solid-state device possessed excellent mechanical exi- Foundation of Department of Education of Liaoning Province
bility, which can be bent into various angles without a notable (LZD201903 and LFW201904) for the nancial support of this
loss of performance and its electrochemical performance was work.
investigated by CV. Apparently, no obvious shape change was
ꢂ
ꢂ
ꢂ
observed in the CV curves shown at angles of 0 , 30 , and 90
inset of Fig. 7e); at the same time the solid-state supercapacitor
References
(
was subjected to continuous bending tests for 500 times, with
only 8.2% capacitance loss (Fig. 7e), which indicated the stable
mechanical properties and promising utilization as a exible
energy-storage device. The PCN-224@PEDOT/PMo12–CC-II elec-
trode also showed excellent stability aer bending. As shown in
Fig. S15b,† aer 500 times of bending, the areal capacitance of
1 D. W. Feng, T. Lei, M. R. Lukatskaya, J. Park, Z. Huang,
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ꢀ
2
PCN-224@PEDOT/PMo –CC-II is 3662.8 mF cm , which was
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1
2
89.9% of the initial capacitance. Meanwhile, the characteristic
peaks of PCN-224@PEDOT/PMo12–CC-II were clearly retained in
the CV curves, which is shown in Fig. S15a.† We further explored
the potential of the exible supercapacitor devices for practical
applications in series and in parallel (Fig. S12b†). Besides,
a three-series device can successfully start up a minifan (Fig. 7f
and ESI video†) and lighted up one blue light-emitting diode
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(
LED) (inset of Fig. 7d), which displayed great potential for the
7 R. R. Salunkhe, Y. V. Kaneti, J. Kim, J. H. Kim and
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practical applications of exible supercapacitor devices.
8
K. M. Choi, H. M. Jeong, J. H. Park, Y. B. Zhang, J. K. Kang
and O. M. Yaghi, ACS Nano, 2014, 8, 7451.
H. J. Peng, J. Raya, F. Richard, W. Baaziz, O. Ersen,
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59, 19602.
4
Conclusions
9
A hierarchical hollow micro-vesicle nanocomposite comprised of
the super-stable MOF, PCN-224 cross-woven by PMo12 and PEDOT,
This journal is © The Royal Society of Chemistry 2021
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