Inorganic Chemistry
Article
−
1
548.0, 513.6, and 493.2 F·g−1 for 2-GCE, and 504.6, 480.4,
1
speed gradually increases from 25 to 200 mV s , the shape of
the CV curve remains substantially constant but shows an
increase in current density, which illustrates the outstanding
Faraday process on the electrode surface and good rate
−
464.7, 444.2, and 424.9 F·g for 3-GCE at the current
−
1
densities of 2.4, 4.8, 9.6, 14.4, and 19.2 A·g . The areal
capacitances (C ) are 182.4, 175.0, 166.6, 163.9, and 151.2 mF·
cm for 1-GCE, 178.0, 176.0, 161.7, 151.5, and 145.5 mF·
a
33,65
−2
performance of sandwich-type polytungstates.
From the
−
2
CV curve, we can also see that the cathode peak and anode
peak move slightly in the direction of negative and positive
potential, respectively, which may be caused by the polar-
ization effect of the electrode. As shown in the inset of Figure
, the linear relations between the current of all redox peaks
and sweeping rate demonstrates the kinetics of interfacial
cm for 2-GCE, and 147.4, 141.5, 102.6, 87.3, and 78.1 mF·
2
−
cm for 3-GCE at the same current density as above. In the
case of high current density (19.2), the C and C of 1-3-GCE
can still remain very large values (512.4 F·g and 151.2 mF·
s
a
−
1
−
2
−1
−2
−1
cm (1), 493.2 F·g and 145.5 mF·cm (2), 424.9 F·g and
8
−
2
7
8.1 mF·cm (3)), which reflects the prominent rate
29−35
capability of the sandwich-type polytungstate. With the
increase of current density, the sequential slight decrease of
the C and C values (Figure 9d) can be attributed to the loss
Faraday reaction and the rapid electron transfer speed.
The contrast diagrams of CV curves between 1−3-GCE and
their respective parents’ POM: Na [PW O ]·7H O-GCE
s
a
9
9
34
2
of efficiency of polytungstate in the redox process under large
(
{PW }-GCE), and Na [A-α-HAsW O ]-GCE ({AsW }-
9 8 9 34 9
29,34
current.
In addition, consistent with the results of CV area
GCE) in the voltage range of −0.6−0.6 V at scanning rate
of 25 mV·s are recorded in Figure S16. Compared with CV
of {PW }-GCE and {AsW }-GCE, CV curve of 1-GCE, 2-
−1
comparison, the C values of 1−3-GCE are higher than that of
s
their contrast compounds ({PW }-GCE and {AsW }-GCE),
9
9
9
9
which further illustrates that the C of synthetic derivatives can
s
GCE, and 3-GCE exhibit bigger encircled area than that of
their parent-GCE at the same scanning speed, which suggests
that they have larger capacitance than that of their parent
POMs. Extended CV area indicates enhanced capacitance
performance due to the introduction of multicore transition
metals cluster. In addition, as shown in Figure 8d, the CV area
of 1−3-GCE is in the order of: 1-GCE > 2-GCE> 3-GCE,
indicating that compounds 1 and 2 have a larger capacitance
than that of compound 3. As a result, the introduction of the
transition metal complex and the construction of the 3D
channel assembly can also improve the supercapacitors
performance of sandwich-type polytungstate to some extent.
The galvanostatic charge−discharge at different current
densities of 1−3-GCE was conducted in the potential range of
be increased by introducing multinuclear transition metals into
vacancy POM clusters. The C values of 1−3-GCE are higher
s
than that of amorphous POM-based nanocomposites, such as
2
2
carbonnanotube/Cs-PMo hybrids, POM adsorbed acti-
1
2
23
vated carbon materials, PMo -polyaniline/graphene compo-
sites, polymeric ionic liquid connected POM/reduced
graphene oxide nanohybrids, and {Mo132}-rGO nano-
composite. The higher specific capacitance of compounds
1
2
2
4
2
5
26
1
−3 may be related to the ordered arrangement of the internal
structure of the crystal, which can lead to more rapid and
efficient transfer of the electrons on the electrode surface.
Meanwhile, the C values of 1−3-GCE are also higher than that
s
29−37
of most reported POMs crystal materials (Table S5).
The
superiority of the capacitance performance may be due to the
introduction of transition metal cluster units, which leads to
more abundant redox reactions in multicore sandwich-type
POMs clusters.
−
0.6−0.6 to further evaluate the electrochemical energy
storage performance of synthetic compounds. As shown in
Figure 9, the GCD curves of 1−3-GCE exhibit the voltage
platform corresponding to the CV shape, which indirectly
reflects the Faraday redox behavior derived from tungsten and
the transition metal clusters of sandwich-type polytung-
The cycle stability of GCD is the key parameter to evaluate
the durability and lifetime of a supercapacitor electrode. The
cycling performances of 1−3-GCE, {PW }-GCE, and {AsW }-
2
9−35
9
9
state.
The specific capacitance (C ) values are 618.2,
s
−
1
Figure 10. Capacitance degradation of 1-GCE, 2-GCE, and 3-GCE
−
2
during 3000 cycles at a current density of 2.4 mA·cm . (b) EIS
contrast spectra of 1-GCE, 2-GCE, 3-GCE, and parent POM:
{
AsW O } and {PW O } (Inset: the magnification part of the high
9 33 9 34
frequency range for the EIS spectra).
−
1
(
2.4 A·g ) and voltage range (−0.6−0.6 V). After 1000 cycles,
the C values of 1−3-GCE decreased by approximately 7.56%,
.33%, and 10.72%, respectively, and then by a small amount
s
8
as the number of cycles increased. The capacitance retention
rates of 1−3-GCE are 91.5%, 89.3%, and 87,8%, respectively,
while those of {PW }-GCE and {AsW }-GCE are only 82.1%
Figure 9. GCD curves of 1-GCE (a), 2-GCE (b), and 3-GCE (c) at
current densities of 2.4, 4.8, 9.6, 14.4, and 19.2 Ag . (d) Comparison
−
1
of specific capacitance of 1−3-GCE and parent POM: {AsW O }
9
9
9
33
and {PW O } at different current densities.
and 83.4% after 5000 cycles. Compounds 1−3 show better
9
34
G
Inorg. Chem. XXXX, XXX, XXX−XXX