| The energy consumption and environmental pollution caused by fossil fuel combustion make the development of alternative energy storage technology become an important way to solve the problem.Supercapacitor is a new kind of energy storage device which is friendly to environment and fast to charge and discharge.It is popular because of its high power density and long cycle stability.Electrode materials are an important part of supercapacitors.To obtain supercapacitors with excellent performance,research needs to be carried out from the design and controllable preparation of electrode materials.Polyoxometalates(POMs)are ideal electrode materials for supercapacitors because of their superior proton/electron transfer and storage capacity.Keggin and Dawson type POMs are two of the most classic polyacid structures.Keggin POMs can transfer electrons quickly,and the introduction of V can greatly improve its performance.However,the research on Keggin-type vanadium tungstate hybrid as an electrode material for supercapacitors is still not thorough.It is of great significance to explore the relationship between structure and supercapacitor performance of Keggin-type vanadium tungstate hybrid.In addition,{P2W18}POMs has 18 WV,which has stronger redox capacity,stable precursors,diverse synthesis methods and the material is readily available,making it an excellent pseudocapacitance material.Based on this,in this paper,the precursor hydrothermal method was used to select appropriate organic ligands and transition metals as structural guiding agents and adjust the reaction conditions to prepare a series of six compounds with different degrees of modification.The supercapacitor performance and electrocatalytic properties of the compounds were studied,and the relationship between the composition,structure and performance of the compounds was summarized.By means of elemental composition analysis,IR,TG,XRD,valence bond calculation and single crystal X-ray diffraction technology,the molecular formulas of six compounds were determined as follows:(Hami)(ami)3{[Ag(bipy)]2(ox)}{VW12O40}(1)(Hami)(ami)3(H2py)2[{V0.5O}2{V0.25O}2{VW12O40}]·2H2O(2)(Htriethylamine)3(triethylamine)2{VW12O40}·2H2O(3)(bipy)0.5{Ag(bipy)2}{Ag4(bipy)7}{Na P2W18O62}·H2O(4)(Himi)11(imi)[K{P2W18O62}2]·8H2O(5)(Hpy)(Htetra)5{P2W18O62}(6)(ami=2-aminopyridine,ox=oxalicacid,py=pyrazine,bipy=2,2'-bipyridine,imi=imidazole,tetra=1H-tetrazole)The Keggin type polyanion[VW12O40]3-of compound 1-3 was in situ transformed from phosphotungstate under hydrothermal conditions,compound 1 is a 1-D chain structure with binuclear complex{[Ag(bipy)]2(ox)}as bridging unit,compound 2 is a three-dimensional supramolecular structure with V-cap connected by pyrazine and 2-aminopyridine,and compound3 is an ABAB type three-dimensional network structure modified by the organic ligand triethylamine;Compound 4 is a unique three-dimensional supramolecular structure formed by the tetragonuclear complex{Ag4(bipy)7}linking to the{Na[P2W18O62]2}dimer,and compound5 is a three-dimensional supramolecular network formed by the imidazole ligand linking to the{K[P2W18O62]2}dimer.Compound 6 is a complex three-dimensional supramolecular network co-modified by two ligands,1H-tetrazole and pyrazine.Compounds 1-6 were prepared as glassy carbon electrode and carbon paper electrode,and their supercapacitor performance were evaluated by cyclic voltammetry,galvanostatic charge-discharge,cyclic stability,electrochemical impedance spectroscopy and pseudocapacitance contribution rate.The results showed that compound 1 has excellent electrochemical stability,high specific capacitance(1102.4,914.1,798.3,673.6,613.9 F·g-1when the current density was3,6,9,12,15 A/g,respectively)and capacitance retention(>90%),and excellent pseudocapacitance behavior.It has been proved that the regular pore structure,the introduction of metal complexes and the rich?-?interaction are conducive to the electrode materials showing superior pseudocapacitance properties,and these six materials have potential applications in the practical application of supercapacitors.The six compounds have excellent electrocatalytic activities in electrocatalytic reduction of hydrogen peroxide,which are excellent electrocatalytic materials. |
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