| Anion exchange membrane fuel cell（AEMFC）has attracted much attention because of its low fuel crossover,low catalyst cost,and environment-friendliness.As the core component of AEMFC,anion exchange membrane（AEM）plays a key role in conducting hydroxide and separating active substances at both electrodes.After years of development,the hydroxide conductivity and alkali resistance of AEM have made great progress,but still need to be further improved,and the trade-off between them needs to be further resolved.One of the key problems is that the improvement of its hydroxide conductivity is still strongly dependent on the increase of ion exchange capacity（IEC）,which in turn causes the decrease of alkaline resisitance.The literatures in recent years have shown that the introduction of alkoxy chain in AEM is beneficial to ion conduction.This thesis systematically studies the influence of different alkoxy side chain modifications on membrane performance,alkoxy chain was used to construct connected hydrogen bond network in the membrane,induce cation aggregation,strengthen the hydroxide transport channel and maintain its stability during operation.In addition,the alkoxy chain was combined with different backbone and side chain structures to in-depth optimization of membrane conductivity and stability,thus achieve a better balance between conductivity and stability,and provide theoretical and experimental basis of high-performance AEMs design.The main research works of this thesis are as follows:（1）Verify the strengthening effect of the hydrogen bond network on the ionic conductivity and durability of AEMs.Firstly,DFT simulations and experiments confirmed the high alkaline resistance of alkoxy chain and the water-binding ability of alkoxy chain to form hydrogen bonds.Then introduce alkoxy chain to modify the benzyl imidazolium functionalized polysulfone membrane,which significantly improves the ionic conductivity（13.3 VS 23.7 m S/cm,30°C）.At 60°C,the peak power density of the H2-O2 AEMFC assembled by alkoxy chain modified membrane reached 404 m W/cm2,which is about 4 times that of side-chain-free membrane at similar IEC.At the same time,the stable hydrogen bond network constructed by the alkoxy chain is also beneficial to replace the partially degraded cations to maintain the integrity of the ion transport channels to a certain extent.At a current density of 100 m A/cm2,the discharge time of H2-O2 AEMFC assembled by the alkoxy chain modified membrane is about 8 times higher than that of the side-chain-free membrane at similar IEC.Besides,polar hydroxylated polysulfone and cationized rigid microporous materials were used to prepare a mixed matrix membrane,a room temperature conductivity of 14.3 m S/cm was achieved under ultra-low IEC（0.38 mmol/g）,further verifying the formation of hydrogen bond network and its promoting effect on hydroxide conduction.（2）Introduce alkyl spacer（i.e.the chain connecting the backbone and the cation）to enhance the mobility of the alkoxy extender,and build efficient hydrogen bond network at a low IEC,thereby enhancing the hydroxide conductivity of AEM.Hydroxide conductivity of the prepared SDQEO membrane reaches 87.3 m S/cm at 80°C,which is about 5 times that of DQ（side-chain-free）membrane and 3.2 times that of DQEO（alkoxy extender modification）membrane.The H2-O2 AEMFC assembled by SDQEO yields a peak power density of 393m W/cm2 at 60°C,which is about 3.8 times that of the DQEO.In addition,DFT simulations and experiments confirmed that the introduction of alkyl spacer can weaken the influence of polymer backbone on the alkali stability of cationic groups,and can further improve the alkaline resistance of SDQEO membrane after combining with the alkoxy extender,the conductivity of SDQEO remains 77%after 8 days of treatment at 60°C in 1 M KOH solution,which is about 3times that of the DQ membrane.The output voltage of H2-O2 AEMFC assembled by SDQEO remains 66%after operated for 12 h at a constant current density of 200 m A/cm2.（3）The hydrophilic alkoxy additional side chain and hydrophobic long alkyl extender were co-introduced to membrane to build good hydrogen bond network in the AEM while enhancing its dimensional stability,so that the increase in IEC and conductivity would not restricted by the large water uptake.The prepared dual-grafted mono-quaternized 16C25-3O25 membrane has good hydroxide conductivity（51 m S/cm,80°C）at moderate water uptake（35%）,which is about 5.5 times that of QPPO17 membrane（side chain free）.Further introducing tri-cation structure to increase the IEC moderately to 1.5 mmol/g,the prepared 3QA16C16-3O16membrane has higher hydroxide conductivity（93 m S/cm）at 80°C,the assembled H2-O2AEMFC yields a peak power density of 506 m W/cm2 at 60°C.Due to the electron-donating effect and steric hindrance of long alkyl extender,the prepared 3QA16C16-3O16 membrane have good alkali resistance（91%conductivity remains after being treated in 1 M Na OH at 60°C for 528 h）.The H2-O2 AEMFC voltage remains 61%after operating for 24 h at 200 m A/cm2.（4）By adjusting the length and grafting degree of the alkoxy additional side chain,a polyaryl membrane with ultra-high alkaline resistance was prepared.The quaternized polyaryl membrane was modified by different alkoxy additional side chain,with the increase of chain length and grafting degree,the connectivity of the hydrogen bond network gradually increases,and the availability of the cationic group（the ratio between ionic conductivity and IEC）was significantly improved.When 20%of PEG1000 alkoxy chain was grafted,theσ/IEC value of the PIB-QA80-PEG100020 membrane at 80°C is 59.5（g·S）/（mol·cm）,which is about 2.1 times that of PIB-QA100（alkoxy chain free）membrane.Further confirmed the negative correlation between the alkaline resistance and IEC of AEM,the introduction of ultra-long alkoxy side chains can break the trade-off effect between conductivity and alkaline resistance:the ionic conductivity of PIB-QA80-PEG100020 membrane remained above 99%after being treated in 1M Na OH solution at 80°C for 480 h.（5）The hydrophilic alkoxy spacer was introduced into AEM to promote the formation of high-efficiency ion channels through its flexibility and good hydrogen bond network.The bisethoxy-containing spacer was prone to curling,thereby reducing the free volume in the membrane,thus exhibits lower water uptake（98%vs 162%）and better alkaline stability（the cation remains 89%or 72%after being treated in 1 M Na OH solution at 80°C for 480 h）than that of the single-ethoxy-containing spacer membrane,and hydroxide conductivity is similar（102 bs 107 m S/cm,80°C）.The peak power density of H2-O2 AEMFC using PIB-1O-Pip and PIB-2O-Pip membrane with alkoxy spacer were as high as 947 m W/cm2 and 826 m W/cm2,respectively,after running at a constant current density of 200 m A/cm2 for 24.3 h,the voltage of the latter remains 85%.After that,the ether-free poly（aryl piperidinium）was used as the backbone to construct a bis-piperidinium AEM containing bisethoxy spacer to increase the local concentration of cations.The prepared m-PTPip-2O membrane is better than mono-piperidinium PIB-2O-Pip membrane that achieves a higher hydroxide conductivity（106 m S/cm,80°C）at a lower water uptake（83%）,the peak power density of H2-O2 AEMFC using this membrane was as high as 868 m W/cm2. |
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