Preparation And Properities Of Bi-guanidinium Functionalized Polysulfone Anion Exchange Membranes

Recently, alkaline anion exchange membrane fuel cell (AAEMFC) have attracted extensive attention owing to its advantages such as low fuel permeation, facile oxygen reduction reaction in alkaline medium, convenient water management, and the usability of non-noble metal catalyst. As a critical component of an AAEMFC, anion exchange membranes (AEM) can decide the power and discharge stability of AAEMFC. So far, inferior chemical stability of AAEMFC is one of the key issues to be addressed. To solve this problem, we propose the following:high water content in the membrane can increase the solvation degree of OH" exchange groups, weakening "hydrogel" into the membrane can "dilute" OH" around ion exchange groups, weakening its attack on the ion exchange groups; at the same time, the enhanced resonance effect of the diphenyl ether biguanidinium structure, while does not have (3-H, can also benefit the chemical stability of AEM.Based on the above ideas, this thesis includes the following main contents:(1) Controlled synthesis of chloromethylated polysulfone. By Friedel-Crafts electrophilic substitution reaction, chloromethylated polysulfone (CMPSf) was synthesized, and through accurate control of reaction conditions, CMPSf with different degrees of chloromethylation were obtained (DC in the range of 0.84-1.37 mmol/g)(2) Design and synthesis of novel quaternizing agent and hydrogel precursors. We synthesized 4,4’-biguanidyldiphenyl ether (ODG) using 4,4’-biaminodiphenylether and vilsmeyer salt as raw material, and synthesized bi-guanidinium-bridged-silsesquioxane (BGBS) using ODG and chloromethyl-trimethoxy-silan as raw material.(3) The preparation of hydrogel-containing biguanidinium functionalized alkaline membrane. Using ODG as the quaternizing reagent, we prepared bi-guanidinium functionalized anion exchange membranes (PSf-ODGOH) through the quaternization reaction, solution castingand alkalization. By introducing BGBS, biguanidinium functionalized anion exchange membranes (PSf-ODG-BGBSOH) with different concents of "hydrogel" were obtained. Scan Electron Microscopy analysis showed that introduction of BGBS lead to the generaction of nanoparticles in situ.(4) Membrane performance study. We analyzed water absorption, swelling ratio, thermal stability, mechanical strength, hydroxide conductivity and other properties of the membranes prepared. The results show that water uptake is significantly increased due to the presence of BGBS in the membrane. We also find that alkaline stability of PSf-ODG-BGBSOH membranes is better than PSf-ODGOH membranes. After immersing in 3 M NaOH solution at room temperature for 20 days, conductivities of PSf-ODGOH membranes and PSf-ODG-BGBSOH membranes decreased by 26% and 38% respectively. And conductivities are, respectively, decreased by 16% and 25% after immersing in 1 M NaOH solution at 60 ℃ for 120 h. The initial decomposition temperature of two kind membranes is about 230 ℃, so the membranes have good thermal stability.This thesis provides new ideas and methods for the design and fabrication of high-performance AEMs. It is potentially useful and meaningful for further development of AAEMFC technology.