| Polyoxometalates(POMs)are clusters formed by metal ions or nonmetal ions through oxygen ions,which can perform multiple electron transfer reactions and have important applications in electrochemistry and catalysis.In the POMs family,research on Keggin-type POMs has attracted much attention.In the presence of functional organic ligands,Keggin-type inorganic-organic hybrids interact with transition metal ions to form multi-dimensional extended structures,which have become suitable candidate materials for electrocatalysis,energy storage and sensor applications.However,most of the known compounds are concentrated on the polyoxy-anions centered on the main group atoms,while the synthesis and properties of Keggin-type compounds and their derivatives centered on metal ions are relatively less studied.Therefore,in this paper,the synthesis of{CuW12O40}based on Keggin structure with copper ion as the center was selected,and the supercapacitor,H2O2 sensing and electrocatalytic water cracking performance of the synthesized compound were also studied.Three crystal compounds with{CuW12O40}as structural unit were synthesized by one-step hydrothermal method.Molecular formula respectively[{Cu(phen)(en)}{Cu(phen)2}(H2CuW12O40)](1)?[{Cu(en)2}2{Cu(en)(phen)}(CuW12O40)](2)and[{Cu(en)2}(H4CuW12O40)](3).In compound 1,[CuW12O40]6-is covalently bonded with[Cu(phen)2]2+and[Cu(phen)(en)]2+to form a double-supported compound,and the 1-D,2-D and 3-D structures are formed by hydrogen bonding,supramolecular interaction and?-?stacking.In compound 2,each[CuW12O40]6-unit is bonded to[Cu(phen)(en)]2+by oxygen terminus to form a 1D helical chain,which forms a 2D lamellar structure by hydrogen bonding between 1D chains,and forms a 3D structure by?-?stacking.In compound 3,the{Cu(en)2}unit bonded to[CuW12O40]6-was connected by hydrogen bond to form a one-dimensional chain,which formed a two-dimensional layered structure in the form of ABAB,and then expanded into a 3D structure through supramolecular interaction.The properties of compounds 1-3 supercapacitors were tested with glassy carbon electrodes in a three-electrode system.At 1 A g-1,the specific capacitances of compounds 1-3 were 572.8,668.1 and 1350.2 F g-1,respectively,and the capacitance retention of compounds 1-3 were 93.3,95.8 and 99.5%(10 A g-1)after5000 cycles,respectively.In a three-electrode system with nickel foam as fluid collector,the specific capacitances of compounds 1-3 at 1 A g-1 were 420.5,437.2 and 586.4 F g-1,respectively,and the capacitance retention rates after 5000 cycles were 82.0%,84.5%and 91.5%,respectively.In addition,compounds 1-3 were also assembled into water-system symmetric supercapacitors using nickel foam as the fluid collector.The energy density and power density of compounds 1-3 were 13.10 Wh kg-1,500.11 W kg-1,21.38 Wh kg-1,500.78 W kg-1;23.36 Wh kg-1,504.38 W kg-1,respectively.The capacitance retention after 5000 cycles were 82.0%,84.5%and 91.5%,respectively.After that,the sensing properties of the three compounds on H2O2were studied.The electrocatalytic efficiencies of compounds 1-3 at 40 m M H2O2 concentration were140.7%,148.3%and 272.2%,respectively.The detection limits of the three compounds were 0.36,0.25 and 0.62?M,respectively.The linear range of the three sensors was wide,and the detection limits were low.The OER properties were investigated using compounds 1-3 as catalyst.When the current density was 10 m A cm-2,the overpotential of compounds 1-3 was 350 m V,248 m V and 230 m V,respectively.The Tafel slopes of compounds 1-3 were 289,269 and 251 m V dec-1,respectively.H6CuW12O40·10H2O was used as a precursor to synthesize three{CuW12O40}complexes modified with 1,3,5-benzylcarboxylic acid(H3BTC)by one-step simple aqueous solution.They are Ag6[CuW12O40]@Ag-BTC(4),Cu3[CuW12O40]@Cu-BTC(5)and Zn3[CuW12O40]@Zn-BTC(6),respectively.The composition,structure and morphology of the synthesized compounds were characterized by infrared spectroscopy(IR),X-ray powder diffraction(XRD),scanning electron microscopy(SEM),Energy dispersive X-ray spectroscopy(EDS),X-ray photoelectron spectroscopy(XPS),specific surface area(BET)and thermogravimetry(TG).The supercapacitors of compounds 4-6were tested in a three-electrode system using nickel foam as the collector.At 1 A g-1,the specific capacitances of compounds 4-6 were 533.6,480.7 and 420.7 F g-1,respectively,and the capacitance retention of compounds 4-6 after 5000 cycles were 92.4%,90.7%and 89.8%,respectively.In addition,compounds 4-6 were also assembled into water-system symmetric supercapacitors using nickel foam as the fluid collector.The energy density and power density of compounds 4-6 were 35.7 Wh kg-1,11.1 Wh kg-1,474.7 W kg-1,628.71 W kg-1;6.9 Wh kg-1,363.6 W kg-1.After 5000 cycles,the capacitance retention rates were 96.5%,94.2%and 91.3%,respectively.After that,compounds 4 and 5 were tested for H2O2 sensing performance.The catalytic efficiencies were 181.8 and 112.5%,and the detection limits were 0.48 and 0.59?M,respectively.The OER properties of compounds 4-6 were investigated.When the current density was10 m A cm-2,the overpotential of compounds 4-6 was 110 m V,170 m V and 334 m V,and the slope of Tafel was 135,200 and 335 m V dec-1,respectively.These results showed that the six compounds have good performance of supercapacitor,H2O2 sensor and electrocatalytic oxygen evolution. |
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