Composites
of polyoxometalate (POM)/metallacalixarene/graphene-based
electrode materials not only integrate the superiority of the individual
components perfectly but also ameliorate the demerits to some extent,
providing a promising route to approach high-performance supercapacitors.
Herein, first, we report the preparations, structures, and electrochemical
performance of two fascinating POM-incorporated metallacalixarene
compounds [Ag5(C2H2N3)6][H5 ⊂ SiMo12O40]
(1) and [Ag5(C2H2N3)6][H5 ⊂ SiW12O40] (2); (C2H2N3 = 1H-1,2,4-triazole). Single-crystal X-ray diffraction
analyses illustrated that both 1 and 2 possess
intriguing POM-sandwiched metallacalix[6]arene frameworks. Nevertheless,
our investigations, including the electrochemical cyclic voltammetry,
galvanostatic charge–discharge tests, and electrochemical impedance
spectroscopy, reveal that the oxidation ability of the Keggin ions
is a primary effect in electrochemical performance of these POM-incorporated
metallacalixarene compounds. Namely, the electrodes containing Mo
as metal atoms in the Keggin POM shows much higher capacitance than
the corresponding W-containing ones. Moreover, compound 1@graphene oxide (GO) composite electrodes are fabricated and systematically
explored for their supercapacitor performance. Thanks to the synergetic
effects of GO and POM-incorporated metallacalixarenes, the compound 1@15%GO-based electrode exhibits the highest specific capacitance
of up to 230.2 F g–1 (current density equal to 0.5
A g–1), which is superior to majority of the reported
POM-based electrode materials.
To enhance energy storage performance via modulation of crystal structure on the molecular level, two series of triethylamine (TEA)‐dependent polyoxometalate (POM) based inorganic‐organic hybrid compounds, [CuII(btx)2]2[SiW12O40] (SiW‐1), [CuI(btx)]4[SiW12O40] (SiW‐2), [CuI4(btx)3][SiW12O40] ⋅ 2H2O (SiW‐3), [{CuII6(btx)7(H2O)12}H4⊂(W12O40)2] ⋅ 12H2O (W‐1), [{CuII7(btx)8(H2O)10}H2⊂(W12O40)2] ⋅ 2H2O (W‐2) and [{CuII10CuI2(btx)11(H2O)16}H2⊂(W12O40)3] ⋅ 6H2O (W‐3) (btx=1,4‐bis(triazol‐1‐ylmethyl)benzene) have been synthesized and explored as pseudocapacitor electrode materials. Compared to other compounds, SiW‐2 shows a specific capacitance of 110.3 F g−1 at 3.0 A g−1 and only experiences a capacitance loss of 13 % after 1000 cycles at a current density of 18.0 A g−1. More importantly, the two series of compounds can be considered as a model for studying the effects of the molecular structures on the pseudocapacitor performance. The result verifies that besides the type of POM, the capacitance ability of the POM‐based compounds is mainly dominated by the connecting modes of adjacent POM building blocks and the dimension of covalent networks formed by POM building blocks. Thus, this work may open a new avenue to optimize the performance of POM‐based capacitors.
To investigate the relationship between the structures
of polyoxometalate
host–guest materials and their energy-storage performance,
three novel polyoxometalate-based metal–organic compounds,
[Ag10(C2H2N3)8][HVW12O40], [Ag10(C2H2N3)6][SiW12O40], and [Ag(C2H2N3)][Ag12(C2H2N3)9][H2BW12O40] are synthesized by a one-step hydrothermal
method and further confirmed by single-crystal X-ray diffraction analyses
and other numerous characterization techniques. In compound [Ag10(C2H2N3)8][HVW12O40], the Keggin clusters are intersected into
channels formed by a 3D open metal–organic framework. In contrast,
in compounds [Ag10(C2H2N3)6][SiW12O40] and [Ag(C2H2N3)][Ag12(C2H2N3)9][H2BW12O40], the Keggin clusters are encapsulated into silver-triazole metal–organic
nanocages to construct core–shell structures, which are further
fused together by covalent bonds to form 3D polyoxometalate-based
metal–organic frameworks. The electrochemical properties of
three compound-based electrodes are estimated by cyclic voltammetry,
galvanostatic charge–discharge, electrochemically active surface
area, and electrochemical impedance spectroscopy. The results of the
electrochemical performance tests indicate that these compounds possess
high specific capacitance and cycling stability, especially [Ag10(C2H2N3)8][HVW12O40], showing a specific capacitance of 93.5 F
g–1, which is higher than that of many other polyoxometalate-based
electrode materials. A possible mechanism of the electrochemical performance
is explored, which is mainly related to the redox capacity of polyoxometalate,
the electrochemically active surface area, the electrochemical impedance
spectroscopy, and the microstructures of polyoxometalate-based metal–organic
frameworks.
state-of-the-art electrocatalysts for HER, but their potential utilization is significantly impeded because of the scarcity and high-price. [5,6] Thus, a promising avenue is to create non-noble electrocatalysts with high-efficiency, low-cost, and long-durability for boosting the HER. In recent years, the non-noble electrocatalysts, such as carbides, [7-10] nitrides, [11-15] oxides, [16-19] phosphides, [20-28] sulfides, [29-37] selenides, [38,39] and carbonbased materials [3,40] have been explored for HER to substitute Pt-group metals, and prominent achievements have achieved. Among these newly developed electrocatalysts, molybdenum disulfide (MoS 2) has attracted tremendous attention as one of promising nonprecious metal candidates for HER due to its unique grapheneshaped 2D structure, proper ΔG H* , low cost, and simple synthesis method. [29-34] However, MoS 2 has two main bottlenecks, including few
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