Novel Crystalline Porous Materials: Design,synthesis And Ion Conductivity Properties

Solid-state electrolytes can conduct lithium ions,hydrogen ions,and hydroxide ions in the solid state.Compared with liquid electrolytes,solid-state electrolytes have higher safety and stability and have important potential for applications in fuel cells and lithium-ion batteries.Crystalline porous materials such as metal organic framework materials（MOFs）and hydrogen bonded framework materials（HOFs）are highly ordered materials with controllable pore size and tunable surface properties,which have wide application prospects in ion conduction.Moreover,crystalline materials are highly advantageous for elucidating the conduction mechanism due to their well-defined structural features.The HOFs system has an inherent intermolecular hydrogen bonding network,which is very promising to obtain materials with excellent proton conduction properties through rational design.The better proton conduction performance of HOFs under low temperature and high humidity conditions is due to the water molecules that can facilitate the proton conduction in HOFs.However,the proton conduction performance of HOFs is limited at high temperature and low humidity conditions.At present,the application of HOFs in systems above 100°C and without water vapor has not been extensively studied.To solve this problem,we have achieved proton conduction above 100°C without water vapor by introducing a guest molecule into HOFs and a“two-in-one”ligand design strategy to modulate the hydrogen bonding network as follows:（1）Three hydrogen-bonded organic layer materials（HOL,HOL-H₂O and HOL-DMSO）based on 4-aminobenzenesulfonic acid and different guest molecules were constructed and their proton conduction properties were investigated.The difference in the guest molecules resulted in a large difference in the proton conductivity from 10^-9（HOL）to 10^-2 S cm^-1（HOL-DMSO）.In HOL-DMSO,DMSO molecules play an important role to separate the structural protons more effectively and facilitate subsequent structure reorganization process,contributing to the superprotonic conductivity,which is as high as 4.42×10^-2 S cm^-1 at 120°C under anhydrous condition.（2）A new crystalline hydrogen-bonded organic framework material（HOF-SXU-1）was developed by integrating two different proton donors and acceptors into a single molecule.HOF-SXU-1 features a remarkable proton conductivity as high as 6.32 m S cm^-1 and an extremely low activation energy of 0.16e V at 160°C under anhydrous N₂ conditions.By constrast under identical conditions,the organic precursors of HOF-SXU-1 only exhibit negligible proton conduction performance,demonstrating that formation of HOF is crucial for excellent proton conduction performance.Metalloorganic frameworks（MOFs）are another structurally designed crystalline porous material,and in the past decade,MOFs have been developed into a new type of ionic conductor.Among the various MOF-based electrolytes,single Li-ion conducting MOFs have been shown to have high Li-ion transference number and excellent ionic conductivity,making them ideal candidates for solid-state electrolytes.However,the conventional methods for constructing single Li-ion conducting MOFs are mainly based on ion exchange,which has the disadvantages of long ion exchange time,insufficient ion exchange,and the need for multiple repetitions.On the other hand MOF-based hydroxide ion conductors are attracting increasing attention in the design of low-cost efficient alkaline fuel cells.However,since the majority of MOFs cannot withstand high concentrations of hydroxide ions and decompose,only a very small number of MOFs can meet such requirements.Accordingly,in order to better address the challenges in practical applications,this dissertation is devoted to the design of novel solid-state electrolytes with excellent conduction properties through the controlled construction of crystalline porous materials that conform to ionic conduction properties,and innovations in structural design and synthesis methods,as follows:（3）To improve the synthesis efficiency of single lithium-ion conducting MOFs,a novel strategy based on rapid acid-base neutralization reactions carried out between strong acids and strong bases has been proposed.A series of MOF-based solid electrolyte materials containing a high density of single lithium ions were constructed using this strategy,and their lithium ion conductivity properties were investigated.The Ui O-66-SO₃Li MOF exhibits a high transference number of 0.94 and conductivity of 7.84×10^-4 S cm^-1 at room temperature.The success in single lithium-ion conducting Ui O-66-COOLi and Ui O-66-2COOLi synthesis also demonstrate the universality of this acid-base reaction strategy to construct MOF-based solid-state single-lithium ion conductors.（4）A stable Cu（I）MOF（SXU-120）was synthesized from cheap melamine（SXU equals Shanxi University）.SXU-120 features ultrahigh stability even in 10 M KOH solution and high density of uncoordinated-NH₂ and-C=O groups.The OH^-conductivity of SXU-120·0.6 KOH reaches as high as 0.49 S cm^-1 at 90°C under full humidity,which is the highest among reported MOF based OH^-conductors so far.It can maintain a constantly high conductivity even after 100 hours at 90°C with negligible performance loss,demonstrating its excellent durability.The adsorbed water molecules,high density of uncoordinated-NH₂ and-C=O groups,and naturally charge separated state of SXU-120 are the keys for the efficient OH^-conduction.（5）A Cd（II）metal-organic framework（MOF）SXU-4 was developed using a“two-in-one”ligand with Cd（II）.Unfortunately,it did not achieve the expected ionic conductivity,but it can detect trace amounts of DMSO in various solvents.DMSO is a commonly used solvent in various synthetic reactions,and trace amounts of DMSO residues are often visible on the surface of chemical products,making it difficult to quickly determine whether the residual DMSO has been completely cleaned.Fluorescence experiments have shown that it has high selectivity and sensitivity to the fluorescence effect of DMSO,which suggests that it can be used as an effective luminescence probe to quickly detect the purity of chemical products by detecting washed solutions.Using the single-crystal structure DMSO@SXU-4,combined with the calculation results,it was found that the enhancement of DMSO-MOF conjugation through the interaction and charge rearrangement of multiple DMSO-MOF supramolecules is the main reason for the fluorescence enhancement.