| Proton conductor is a kind of solid electrolyte that can conduct hydrogen ions.It has good conductivity at room temperature and has a wide range of applications in fuel cells and hydrogen sensitive components.Crystalline materials such as metal organic frameworks,porous coordination polymerizations and covalent organic frameworks,as new proton conductors,have made great progress in recent years because of their excellent structural adjustment properties.However,these materials also have some shortcomings that cannot be ignored.For example,the synthesis of metal organic frameworks and covalent organic frameworks is more difficult,the cost is higher,and the yield is generally low,and the water retention of porous coordination polymers is not good enough and leads to poor intrinsic conductivity.Therefore,it is still of great significance to develop and synthesize crystalline proton conductor materials with low cost and excellent performance.Polyoxometalates are a kind of clusters formed by connecting early-transition metal ions through oxygen bridges.They have the advantages of simple synthesis,clear structure,gain and loss of one or more electrons without the structure unchanging.It is a kind of potential high crystalline material with proton mobility.Furthermore,the use of organic ligands to covalently modify polyoxometalates can not only improve the stability of clusters and increase the diversity of the structure,but also use the synergistic effect between organic molecules and inorganic anion clusters to expand hybridization.As a class of excellent organic ligands,triol compounds can be covalently connected to polyoxometalates through three C-O-M bonds,which have a matching structural configuration and higher bonding energy between them and the cluster compound.It can not only stabilize the structure of polyoxometalates,but also facilitate the further assembly of the obtained organic-inorganic hybrids to obtain a specific network structure.In the existing work,triol ligands are used more in Anderson-type polyoxometalates or vanadium-substituted Dawson-type polyoxometalates,but less used in Keggin-type clusters,and little attention has been paid to the proton conductivity properties of organic covalently modified products.In this paper,vanadium-molybdenum clusters are selected as the research system,and a series of organic-inorganic hybrid products modified by triol ligands have been successfully obtained by selecting triol ligands with different functional groups.The introduced organic ligand has an obvious stabilizing effect on the structure of the synthesized cluster compounds.At the same time,by adjusting the cation,crystalline materials with different extended structures are successfully obtained and exhibit good proton conductivity.The main research results of this paper include:1.Three kinds of Keggin-type polyoxometalates covalently modified by triol ligands with different functional groups were synthesized by one-pot method,(NH4)6{VMo9O31[CH3C(CH2O)3]}·9H2O(1),(NH4)6{VMo9O31[CH3CH2C(CH2O)3]}·9H2O(2),(NH4)6{VMo9O31[HOCH2C(CH2O)3]}·9H2O(3).The single crystal structure analysis shows that the obtained compounds are trivacant Keggin-type polyoxometalates with vanadium as a heteroatom,and the triol ligand is connected to the vacant cluster via three C-O-Mo bonds.Th triol ligand not only successfully stabilizes the tri-vacant{VMo9O34}unit,but also retains the active site of the lacunary position,providing the possibility for further modification and reaction.The tri-vacant{XMo9O34}(X=Si,P,V)unit cannot exist alone and stably,and in the previous literature,a sandwich structure is generally formed by introducing additional metal ions to connect the active oxygen at the vacancy site.The present research provides a new idea for the stability of such compounds.Further research showed that under the conditions of 343 K and 30%humidity,the conductivity of the three compounds were 1.15×10-5 S cm-1,1.02×10-5 S cm-1,5.7×10-5 S cm-1,respectively.The low proton conductivities are attributed to the fact that the counter cation ammonium can not provide a favorable chemical environment for the effective circulation of protons.2.In order to optimize the proton conductivity of the polyoxometalate crystalline material,a class of vanadomolybdates covalently modified by triol ligand{V2Mo2O10}units,(H3NCH2CH2NH3)2{V2Mo2O10[HOCH2C(CH2O)3]2}·4(H2O)(4),Na2(H3O)2{V2Mo2O10[CH3C(CH2O)3]2}·8(H2O)(5),Na4{V2Mo2O10[OHC(CH2O)3]2}·11(H2O)(6)and Na4{V2Mo2O10[CH3CH2C(CH2O)3]2}·11(H2O)(7)were synthesized.In this type of compound,two triol ligands stabilize the{V2Mo2O10}unit through the C-O-M(M=V,Mo)bond.In compound 4,the counter ion is protonated ethylenediamine,and the hydrogen bond between cations and the polyanions promotes the formation of a two-dimensional planar structure.In compound 5,sodium ions and hydrogen ions are used as counter ions.Thus,a three-dimensional structure with pores in specific directions is formed.When only sodium ions are used,no matter whether the terminal group of the triol ligand is methyl(compound 6)or hydroxyl(compound 7),only three-dimensional structures without pores in specific directions are obtained.structure.The AC impedance test results show that under the condition of 368 K and 98%humidity,the conductivity of compounds 4 and 5 with layered or columnar pores in the structure are2.5×10-2 S cm-1 and 1.72×10-2 S cm-1,respectively.The conductivity of compounds 6and 7 without pores in specific directions are 2.6×10-3 S cm-1 and 6.31×10-4 S cm-1,respectively.The above studies show that the existence of one-dimensional or two-dimensional channels in crystalline materials play a vital role in the provision of proton conductivity.In this thesis,by applying triol ligands to the vanadomolybdate system,on the one hand,a series of organic group covalently modified crystalline materials with novel structures were synthesized,and on the other hand,by adjusting the structure,high proton conductivity was obtained,as well as the relationship between structure and conductivity.The above work provides new ideas and methods for the design of new proton conductive materials,and promotes the application of polyoxometalate crystalline materials in proton conduction. |
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