Preparation And P Roperties Of Novel Side-chain And Self-crosslinked Anion Exchange Membranes

Alkaline anion exchange membrane fuel cells（AAEMFCs）have attracted wide attention due to their enhanced redox reaction kinetics and the use of non-noble metals as catalysts.As one of the key components of AAEMFCs,alkaline anion exchange membrane（AEM）can separate the anode and cathode to avoid short circuit,meanwhile OH^-can selectively penetrate through the AEM.Until now,the main challenges of AEM research are low conductivity and poor alkaline stability.Therefore,two types of anion exchange membranes,i.e.side-chain-grafted AEM and self-crosslinked AEM,were prepared in this thesis.The side-chain-grafted structure can promote the formation of microphase separation and construct interconnected ion channels.The self-crosslinked structure possesses tunable crosslinking degree and grafting density,thus the conductivity and dimensional stability can achieve a better balance.The main contents of this thesis are as follows:（1）Preparation and properties of side-chain-grafted anion exchange membrane（MmOH-PSf-VS）.First,diolefin structure was obtained from the reaction of N-methyldiallylamine and chloromethylated polysulfone（CMPSf）.Then 4-vinylbenzyl chloride（VBC）and styrene（ST）were alternately grafted onto the diolefin structure by free radical polymerization,followed by quaternization and alkalization.By controlling the amount of VBC and ST,a series of MmOH-PSf-VS membranes with different grafting lengths were prepared.Good microphase separation was achieved due to special side-chain-grafted structure.Under the similar IEC,the conductivity of MmOH-PSf-VS-12(33.71 mS cm^-1,20°C)was 33.9%higher than that of un-grafted anion exchange membrane(MmOH-PSf,25.17 mS cm^-1);moreover,the side-chain-grafted anion exchange membrane exhibited better alkaline stability owing to the low grafting density,the retention of IEC of MmOH-PSf-VS membrane was80%after it was immersed in 1 M NaOH solution at 60°C for 288 h.（2）Preparation and properties of self-crosslinked anion exchange membrane（Cro-N-PSf）.Cro-N-PSf membranes were obtained from the d iolefin structure by thermal crosslinking.A series of Cro-N-PSf membranes with different grafting density and crosslinking degree were prepared by controlling the degree of chloromethylation of CMPSf and crosslinking time.The degree of crosslinking can directly influence the conductivity,dimensional stability,and mechanical properties of the membranes.For Cro-N-PSf-172membranes with the same grafting density,when the crosslinking time is 80 minutes,the membrane exhibited higher conductivity,reaching 24.07 mS cm^-1 at 20°C and 53.73 mS cm^-1 at 80°C.Compared with non-crosslinked N-PSf membranes,Cro-N-PSf membranes showed better dimensional stability.The water uptake and swelling ratio of Cro-N-PSf-172-80min membrane remained unchanged from 20°C to 80°C,respectively24%and 13%at 80°C.The mechanical strength of Cro-N-PSf membranes was also enhanced significantly after crosslinking.The Cro-N-PSf-102-80min membrane exhbited a good tensile strength of 47.80 MPa,showing good mechanical properties.In this thesis,side-chain-grafted and self-crosslinked anion exchange membranes were respectively obtained from free radical polymerization and thermal crosslinking on the basis of olefin structure.The conductivity,water uptake and swelling ratio,and alkaline stability of the the two anion exchange membranes were investigated.After analysis and comparision,it is found that side-chain-grafted structure is beneficial for conductivity and alkaline stability of the membrane,while the self-crosslinked structure is more beneficial for the dimensional stability and mechanical properties of the membrane.