| Supercapacitor is a new type of energy storage device,and its research and development play an important role in promoting new energy technology.The electrode materials are the core of the whole supercapacitor device,which determine the performance of the capacitor.Therefore,finding electrode materials with excellent performance is the key to improve the performance of supercapacitors.Polyoxometalates(POMs)have the properties of reversible electron transfer,and their structures are still stable after multiple steps of rapid electron transfer.Therefore,POMs have obvious advantages and broad application prospects as electrode materials for supercapacitors.However,due to the high solubility and low conductivity of traditional POMs,their cyclic stability and capacitance performance are still unsatisfactory.Based on this,in this paper,we first used crystal engineering methods and the ideas of molecular recombination and clipping.We employed classic POMs as the main raw materials and combined them with specific metalorganic subunits.Through the use of the "bridge" and synergistic effects of the metalorganic subunits,we designed and synthesized twelve novel polyoxometalate-based metal-organic complexes(POMOCs)with well-defined structures and multiple active sites,which have not been reported before.Single crystal materials of POMOCs and their PEDOT composites were prepared.The crystal structures of the twelve POMOCs were characterized using single crystal X-ray diffraction and other techniques.These materials were used as electroactive substances to construct various high-performance supercapacitor electrodes.The electron transfer performance between POM clusters and the stability of POM electrodes were improved,which compensates for the shortcomings of a single POM molecule in the field of supercapacitors.Specific research contents are as follows:1.Keggin-type tungstate was used as a POMs source to react with selfsynthesized organic ligands 1-pyridine-3-methylene-1H-benzotriazole(pybta),1imidazole-1-methylene-1H-benzotriazole(imbta)and metallic silver salts.Four kinds of tungsten POMOCs crystal materials that have not been reported were prepared by hydrothermal synthesis method after adjusting by mineralizing agent sodium metadadate and triethylamine:Ag4(pybta)4(PWⅤWⅥ11O40)(1)Ag4(pybta)4H(SiWⅤWⅥ11O40)(2)Ag4(imbta)4(PWⅤWⅥ11O40)(3)Ag4(imbta)4H(SiWⅤWⅥ11O40)(4)The results of structural analysis indicate that compounds 1 and 2 show a 3D multi-helix infinite entanglement frame structures.Compound 3 presents a 2D layer structure containing POMs.Compound 4 has a 1D chain structure that formed by series of organo-metal ligand rings using silicotungstate anion as template.The supercapacitor performance of 1-4 electrode materials were investigated in a threeelectrode system.The test results show that they have good supercapacitor performance and cycle stabilities.The results of cyclic voltammetry(CV)and constant-current charge-discharge(GCD)tests show that when the current density is 7 A·g-1,the specific capacitances of electrode materials 1-4 are 288,253,236 and 194 F·g-1,respectively.The measured capacitance retention rates are 77.7%,74.2%,76.1%and 72.7%,respectively,when the current density of 10 A·g-1 is continuously charged and discharged for 1000 cycles.The results indicate that electrode materials 1-4 have good supercapacitor performance and cycle stabilities.2.Use Keggin-type phosphomolybdic acid as the POM source with higher redox activity,and remain the metal salt and organic ligands constant.Through optimizing the hydrothermal reaction temperature,pH value,and the type of mineralizer that affects the ligand’s coordination ability,we prepared four novel molybdenum-based POMOCs which have not been reported:Ag4(pybta)4(PMoⅤMoⅥ11O40)(5)Ag4(imbta)4(PMoⅤMoⅥ11O40)(6)[Ag2H7(pybta)6(PMo12O40)3]·12H2O(7)[AgH2(imbta)2](PMo12O40)(8)Among them,Compounds 5 and 1,6 and 3 are two groups of hetero-isomorphic crystals.Compounds 7 and 8 are supramolecular structures,the isolated POMs clusters are connected to the metal-organic units in order through hydrogen bonding and π…π interaction to form stable steric conformation.The GCD test results show that when the current density is 1 A·g-1,the specific capacitance of electrode materials 5-8 is 668,420,408 and 320 F·g-1,respectively.The measured capacitance retention rates are 91.4%,84.1%,86.2%and 70.0%,respectively,when the current density of 10 A·g-1 is continuously charged and discharged for 1000 cycles.It is found that the similar composition of the POMs electrode materials,in general,the higher the crystal structure dimension,the richer the microscopic composition of the hydrogen bond network,the more conductive electron transmission,the better the capacitance performance of the electrode materials.3.Keggin-type phosphomolybdate or ammonium molybdate is selected as the reaction raw materials,the organic ligands are fixed,and the silver ion is modulated as copper ion with smaller radius,so as to reduce the coordination number between the organic ligands and metal ions by using steric hindrance effect,obtain more hydrophilic unsaturated sites,induce the formation of water clusters and hydrogen bond networks.Design and prepare a series of molybdenum copper based POMOCs containing water clusters getting compounds 9-12:[Cu2(H2O)4H2(imbta)4](PMo12O40)2·6H2O(9)[Cu(H2O)2H4(pybta)4](PMo12O40)2·2H2O(10)[Cu2H4(pybta)2(H2O)2](Mo8O28)(11)[CuH2(imbta)2(H2O)2](Mo8O26)(12)Compound 9 formed a 3D supramolecular structure of the "POMs-dinucleated copper-organic complex-POMs" layer of encapsulated water cluster.In compound 10,water clusters are connected to POMs by hydrogen bonds to form 2D planar structures.Compounds 11 and 12 are also making the 1D chains extend into 3D supramolecular structures via hydrogen bonding and π…π interaction.When the current density is 1 A·g-1,the specific capacitance is 710,556,542 and 391 F·g-1,respectively.At the current density of 10 A·g-1 for 1000 cycles,the measured capacitance retention rates are 91.2%and 92.2%for compounds 9 and 10.Considering the specific capacitance value and cyclic stability,Comound 9 shows better supercapacitor performance.4.PEDOT was oxidized and polymerized on PMo12-Cu-imbta/CC by electrochemical deposition,and PEDOT/PMO12-Cu-imbta/CC composite was prepared.Through XPS test,it was found that PEDOT and PMo12-Cu-imbta had obvious electron transport and significant interaction during oxidative polymerization.By investigating the electrodeposition voltage window and electrodeposition time in detail,it is determined that the voltage window is 0-1.4V vs.Ag/AgCl and the electrodeposition time is 560 s(4 turns).The specific capacitance of the prepared PEDOT/PMo12-Cu-imbta/CC composite electrode material is 902 F·g-1 at 1 A·g-1 current density,and the capacitance retention rate remains as high as 95.1%after 1000 cycles of charging and discharging at 10 A·g-1 current density.A double-electrode asymmetric supercapacitor device was assembled using a composite material of PEDOT/PMO12-Cu-imbta/CC as the positive electrode and activated carbon as the negative electrode.The assembled PEDOT/PMo12-Cuimbta/CC//AC device exhibited a power density of 698.3 W·kg-1 at an energy density of 17.4 Wh·kg-1.This indicates that the synergistic effect between PEDOT and PMo12-Cu-imbta is significant,and the composite material shows excellent specific capacitance performance and good electrochemical stability. |
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