Preparation And Performance Study Of New High-performance Polycarbazole-based Anion Exchange Membrane

As the core of"hydrogen-to-electricity conversion",fuel cells can convert hydrogen energy into electricity in a clean and efficient manner.Among them,polyelectrolyte membrane fuel cells can be divided into two types according to their internal transport ions,namely anion exchange membrane fuel cells(AEMFCs)and proton exchange membrane fuel cells(PEMFCs).Compared with PEMFCs,which requires the use of precious metal catalysts,AEMFCs is gradually becoming a hot research topic because of its high oxygen reduction reaction(ORR)activity,which allows the use of non-precious metal catalysts and thus reduces costs.As one of the key materials of AEMFCs,the main role of anion exchange membrane(AEMs)is to transfer hydroxide ions and isolate anode and negative fuel,so the development of AEMs with high performance and long life is very important for the application of AEMFCs.The AEMs still suffer from poor chemical stability and insufficient mechanical properties.In order to address the above issues,this thesis uses various membrane structure design optimization strategies(e.g.,block copolymerization,remote grafting,cross-linking,etc.)to optimize the membrane performance.A series of polyarylene-based AEMs were prepared based on carbazole and its derivatives,and the conformational relationships of AEMs were investigated in detail.The specific research of this thesis is as follows:(1)Study of hydrophobic unit-containing poly(carbazole-butanedione)membranes(HOCB-TMA-x)A series of poly(carbazole-butanedione)polymer backbones based on carbazole were prepared by a"block copolymerization"and"remote grafting"strategy.AEMs containing different ratios of hydrophobic units were prepared by grafting trimethylamine cations.The presence of hydrophobic units and the incorporation of alkyl side chains can effectively improve the dimensional stability,mechanical properties,alkali stability and ionic conductivity of the membranes.HOCB-TMA-30 exhibited optimal performance:its OH~-conductivity reached 152.9 m S/cm at 80℃.The HOCB-TMA-30 hydroxide ionic conductivity was reduced by only 9.5%after 2250 h of immersion in 1 M Na OH aqueous solution(80℃).The maximum power density achieved by HOCB-TMA-30 at 80℃was 1.85 W/cm~2 and the current density was 4.38A/cm~2.(2)Study of poly(carbazole-trifluoroacetone)membranes(HOF-QA)containing different cationsBased on the study in the previous chapter,a series of poly(carbazole-trifluoroacetone)(HOF-QA)anion exchange membranes containing different cations were prepared to increase the flexibility as well as the overall performance of the membranes.The introduction of 1,1,1-trifluoroacetone can effectively improve the dimensional stability of AEMs as well as the microphase separation within the membrane,and AEMs based on fluorine-containing backbones grafted with different cations exhibited excellent properties in different aspects.Among them,the cationic degradation of HOF-IMI membrane is up to 300℃.The HOF-TMA membrane sample exhibited relatively excellent mechanical properties with an elongation at break of 25.5%and a tensile strength of 53.2 MPa.The ionic conductivity of HOF-TMA was160.4 m S/cm at 80℃.After 1500h alkaline resistance test(2 M Na OH aqueous solution at 80℃),the ionic conductivity of HOF-PIP membrane was only decreased by 11.1%.(3)Study of multi-cations-crosslinked poly(p-terphenyl-carbazole-piperidine)membranes(CTCPQ-X)Based on the studies in the previous two chapters,the polymer backbone was prepared by block copolymerization of carbazole derivatives,p-terphenylene and 1-methyl-4-piperidone,followed by cationic grafting and crosslinking with a multi-cation crosslinker.The cross-linked structure can effectively increase the mechanical properties as well as the dimensional stability of AEMs.The CTCPQ-20 membrane sample exhibited relatively excellent mechanical properties with an elongation at break of 17.4%and a tensile strength of 58.52 MPa.The ionic conductivity of CTCPQ-15 membrane was 144.2 m S/cm at 80℃.After 1500h alkaline resistance test(2 M Na OH aqueous solution at 80℃),the ion conductivity of CTCPQ-20 membrane was only decreased by 14.3%.