Preparation And Properties Of Ion Exchange Membrane Modified By Nitrogen Heterocyclic Ring

Membrane separation technology has the advantages of high efficiency,energy conservation,and environmental protection,and is widely used in proton exchange membrane fuel cells,liquid flow batteries,electrodialysis,and other fields.Proton exchange membranes are the core components of membrane separation,as an alternative of the expensive perfluorinated sulfonic acid membranes（Nafion）,non-fluorinated proton exchange membranes have attracted the interest of researchers.Nitrogen-heterocycles have good thermal and chemical stability,high electronegativity,compact molecular structure,and are easy to form intermolecular hydrogen bonds,which are conducive to prepare high-strength polymers.The Lewis base N atoms of N-heterocyclic can bind protons and serve as proton transport sites;moreover,conjugated planar heterocyclic structures facilitate the formation of large cationic groups after protonation,which can provide good barrier to high-valent cations.In this thesis,different nitrogen-heterocycles were introduced into polymer backbones to improve the separation performance of the proton exchange membranes.1.Preparation of nucleobase crosslinked sulfonated poly（ether ether ketone）（SPEEK）proton exchange membranes for electrodialysis:Sulfonated poly（ether ether ketone）（SPEEK）was used as polymer matrix,and two different nucleobases（thymine T and adenine A）were grafted on the polymer backbone,and then the A and T grafted SPEEK were blended to obtain AT crosslinked SPEEK electrodialysis membranes.After crosslinking,the tensile strength of the membrane increased from 58.3 MPa to 71.7 MPa.Compared to uncrosslinked membrane,the water uptake and swelling degree of the crosslinked membrane were reduced by 50%.The IEC values remained unchanged before and after crosslinking,maintaining between 1.7-1.8meq/g.After the nucleobase crosslinking,the electrodialysis separation flux and selectivity were both improved,breaking the"trade off"effect.The flux of H⁺increased from 5.54×10^-3m/h to 8.83×10^-3m/h,while the selectivity of H⁺/Fe²⁺increased from 175.1 to 255.2.2.Preparation and performance of poly（aryl imidazole）s for all vanadium redox flow batteries:2-and 4-substituted imidazolaldehyde were reacted with biphenyl to prepare 2-and4-substituted poly（aryl imidazole）s（2-MI and 4-MI）via superacid catalysis.Both 2-MI and4-MI exhibited high proton conductivity and good vanadium resistance.In the single cell performance tests,when the current density was 80 m A/cm²,the coulomb efficiency of both2-MI and 4-MI was above 99%.After 50 charge-discharge cycles at a current density of 120m A/cm²,the capacity retention of the 2-MI membrane reached 76.7%,and the value of 4-MI was 78.0%,which was more than 10%higher than that of Nafion 212 membrane（65.6%）,consistent with the permeability of vanadium ions.The self-discharge performance for both2-MI and 4-MI was good,with the self-discharge duration of 2-MI and 4-MI reaching 138.1 h and 160.4 h,respectively,2.0-2.4 times that of Nafion 212.After 1000 charge-discharge cycles,the energy efficiency of all the prepared membranes remained stable and slightly decreased,indicating that the prepared poly（aryl imidazole）proton exchange membranes had a good application prospect in all vanadium redox flow batteries.