Design,Synthesis And Properties Study Of Poly(Aryl Piperidinium)Anion Exchange Membranes

With the development and application of hydrogen energy,the anion exchange membrane fuel cells(AEMFCs),being characterized by cleanness,high efficiency and low cost,has become the research focus in the field of fuel cells.As its core component,anion exchange membranes(AEMs)still face some challenges,such as low hydroxide conductivity,serious water swelling and poor alkaline stability,which have become important factors restricting the development of AEMFCs.Polymers containing aryl ether bond are widely used in AEMs membrane-based polymers because of their easy functional modification and excellent thermal stability,but they are easily attacked by OH~-under alkaline environment.In contrast,"ether-free"poly(arylene piperidinium)with excellent mechanical strength and alkaline stability has a better development prospect in AEMs field.At present,acid-catalyzed Friedel-Crafts reaction without metal and with simple synthesis has become a common strategy for preparing poly(arylene piperidinium).However,the prepared polymer will be difficult to meet the requirements of film casting and application,when the improper monomer selection or synthesis conditions.Therefore,based on the reasonable design of polymer backbone structure and cation functional groups,this paper first explored the synthesis conditions of acid-catalyzed Friedel-Crafts reaction,and poly(arylene piperidinium)copolymer were obtained under suitable synthesis conditions to improve the film-forming property of polymer and the alkaline stability of AEMs.In addition,in order to further improve the OH~-conductivity of poly(arylene piperidinium)AEMs,alkyl side chains separated from cation functional groups were introduced into poly(arylene piperidinium)backbone in paper.The influence of side chain length on properties of comb-shaped side chain poly(arylene piperidinium)AEMs was explored,summarizing effective modification strategies for improving OH~-conductivity.The main research contents and results are as follows:(1)The poly(arylene benzil piperidinium)(PTP-B-x)membrane with excellent film-forming property was prepared by reasonably selecting materials of acid-catalyzed Friedel-Crafts reaction and adopting proper synthesis conditions.P-terphenyl,N-methyl-4-piperidone(m Pip)and diketone monomer benzil were used as materials.PTP-B-x copolymers,being good film-forming property,were prepared by acid-catalyzed Friedel-Crafts reaction,when the aromatic ketone ratio being 1:1.1,the molar ratio of p-aromatic to TFSA being 1:9,the solid loading being about 15 wt%and the catalyst superacid being directly added.PTP-B-x AEMs has good alkaline stability and mechanical strength,and water uptake and swelling ratio changes little with temperature.Different functionalization degrees have different effects on the performance of AEMs.The PTP-B-90membrane with high IEC value(2.47 mmol/g)reaches the highest OH~-conductivity at 80°C,whereas its water uptake is serious.The another problem is the poor water management in cell durability test,which leads to the initial cell performance decline and voltage oscillation phenomenon in battery durability.(2)Comb-shaped side chain poly(arylene indole piperidinium)(PITP-Cn Qx)membrane was obtained by introducing alkyl side chains separated from cation functional groups into poly(arylene piperidinium)with excellent alkaline stability.In order to improve the OH~-conductivity of poly(arylene piperidinium)AEMs and explore the influence of alkyl side chains with different lengths on the comprehensive properties of PITP-Cn Qx membrane,Comb-shaped side chain poly(arylene piperidinium)copolymer was prepared from N-alkylated 2-oxindole under the proper reaction conditions in Chapter 2.The morphology of AEMs was characterized by small angle x-ray scattering(SAXS)and atomic force microscope(AFM).The effect of alkyl side chains with different lengths on the comprehensive performance of PITP-Cn Qx membrane were investigated.PITP-Cn Qx membrane with side chains formed obvious phase separation morphology,which promoted the transmission of OH-,and the water absorption swelling was within a reasonable range,and the battery performance and durability were improved.It was found that with the increase of side chain length,the performance of PITP-Cn Qx membranes increased first and then decreased.In addition,after alkali stability test,piperidine cation was degraded by Hoffman to eliminate nucleophilic substitution ofβ-H andα-C,while after lifetime,it was only degraded by nucleophilic substitution mechanism.