Preparation,Characterization And Properties Study Of Novel Proton-conducting Functional Coordination Polymers

In recent years,metal-organic frameworks(MOFs)as new type of porous hybrid materials have attracted much attention.Because of their structural adjustability,chemical stability,easy assembly and easy to hybrid with other materials,MOFs have shown potential application in the gas separation and storage,magnetism,luminescence,electrical materials,and so on.Proton exchange membrane fuel cell is one of the fuel cells,which is mainly characterized by the proton exchange membrane.Metal-organic framework material due to the diversity and specificity of its structure has attracted many researchers attention in terms of proton conductivity.Through the design and synthesis of some ligands to build metal-organic frameworks,the proton conductivity of materials can be effectively improved.In this thesis,we designed and synthesized two carboxylic ligands by literature.The following work was carried out:1.In order to better introduce the proton source in the complexes,we designed and synthesized a flexible carboxyl ligand 5-(3,5-dimethyl-1,H-pyrazol-4-ylmethyl)isophthalic acid(H3L1).We used this ligand and transition metal copper,cadmium,nickel,zinc salts to synthesize four complexes [Cu(L1)]n(1)、[Cd(L1)]n(2)、{[Ni(L1)(H2O)2]?H2O}n(3)、[Zn(L1)(H2O)]n(4)by solvothermal method.The structure and stability of the complexes were studied by X-ray single crystal diffraction analysis and other basic characterization.Complexes 1,2 and 3 are 2D complexes,and the 2D layered structure form a three-dimensional supramolecular structure by hydrogen bonds and π???π interaction.Complexes 4 is 3D complex,with the 3D two-fold interpenetrating framework forms a hydrophilic channel along a axis,which are rich in hydrogen bonds.Through the study of water resistance and thermal stability,we have chosen the stable complex 4 to investigate the proton conductivity.It was found that the complex has a proton conductivity that depends on temperature under the corresponding humidity conditions.And the proton conductivity reached a maximum of 1.64 × 10-4 S cm-1 at 100 °C under 98% humidity conditions.According to the Arrhenius formula,the activation energy of the complex 4 was found to be greater than 0.4 eV under the humidity condition.Combined with water vapor adsorption experiments,it is presumed that the proton conduction mechanism is as follows: Hydrogen on the pyrazole is utilized as a proton source to the coordination water molecule through the hydrogen bond,and the free water molecules move as a proton carrier inside the hydrophilic channel in the a-axis direction to achieve proton conductivity,which correlates the Vehicular mechanism.2.In order to introduce the proton carrier into the proton to form the proton pathway,we designed and synthesized the 5-phosphonomethyl-isophthalic acid(H4L2).And two complex {[Co(L2)(H2O)2]?H2O}n(5),[Mn2.25(L2)(H2O)3.5(OH)0.5]n(6)was obtained reacted the acid with transition metal cobalt and manganese salt by solvothermal method respectively.In addition,the structure and stability of the two complexes were studied by X-ray single crystal diffraction analysis and basic characterization.5 is a one-dimensional complex with a 1D chain structure formed by the coordination of metal cobalt ions with phosphonic acid.Phosphonic acid oxygen,carboxyl oxygen,coordination water in the 1D structure have a huge hydrogen bonding force with the free water,and then connected to form a 3D supramolecular structure.However,since the complex is not stable with water,proton conductivity can not be studied.Since the complex 6 has good water resistance and thermal stability,its proton conductivity was studied.It was found that the complex exhibited proton transfer behavior under conditions of higher than 68% relative humidity.At 98% humidity,temperature 90 °C,the proton conductivity reached a maximum of 1.67 × 10-3 S cm-1 and the operating temperature range is 30 °C to 100 °C.The proton conduction mechanism of complex 6 was studied by the experimental results of single crystal structure and water vapor adsorption.When the humidity drops to 93% relative humidity,the free water becomes less,the proton conduction mechanism of complex 6 is the vehicleular mechanism.When the humidity reaches 98% RH,the free water becomes more and the proton conduction mechanism of complex 6 is Grotthuss mechanism.