Preparation And Performance Study Of Multi-cationic Polyarylene-based Anion Exchange Membrane

Anion exchange membrane fuel cells(AEMFC)are rapidly developing as a research focus in the field of fuel cells because of their advantages such as fast oxygen reduction reaction kinetics,the possibility of using non-precious metal catalysts such as nickel,low cost,and low fuel permeability compared to proton exchange membrane fuel cells.Anion exchange membrane(AEM)is one of the key components to determine the performance of AEMFC,playing the role of isolating reactants and transporting ions,so AEM must have excellent performance to be suitable for fuel cells.The main challenge currently faced by AEM is the inability to trade-off between ionic conductivity and dimensional stability.To obtain high ionic conductivity,it is usually achieved by increasing IEC,but this often leads to the dissolution and rupture of AEM due to excessive water absorption,which destroys the mechanical properties of AEM.In addition,the alkali resistance stability of AEM is also an urgent problem to be solved.As AEM works in hot alkali environment,the polymer backbone and cationic groups are highly susceptible to nucleophilic OH~-attack and degradation,which reduces the service life.To address the above problems,in this paper,we choose the polymer without ether bond as the main chain to avoid the breakage of polymer backbone caused by OH~-attack on ether bond and improve the alkali stability;the cross-linking strategy can limit the swelling of AEM and the multi-cationic strategy can regulate the ionic conductivity,through these two methods to achieve the purpose of regulating the water absorption and swelling of AEM while achieving a relatively high ionic conductivity.The details of the work are as follows:Firstly,polyarylindole polymers without ether bonds were prepared,grafted with multi-cationic side chains of different grafting degrees,and continuous ion transport channels were constructed by designing pro/hydrophobic microphase separation structures to improve ion conductivity,and PIB-80TQA membrane was obtained by TEM and ion conductivity with the highest ion conductivity of 85.68 m S/cm at 80°C.Then multi-cationic crosslinkers were introduced to construct three-dimensional network structure to transfer OH~-while improving the mechanical properties of AEM.The multi-cationic side chains and the multi-cationic cross-linker worked together to have dimensional stability without sacrificing the ionic conductivity,the WU of PIB-TQA membrane was 18.50%and the SR was 8.58%and the cross-linked PIB-TQA-7Q membrane still had high WU of 27.57%,but the SR did not increase significantly,which was 13.08%.The cross-linked structure inhibited the swelling of AEM and maintained the dimensional stability of AEM.Then,in order to solve the problem of insolubility of chemical cross-linking,we continued our investigation based on the multi-cationic ether-free backbone system by accessing urea groups and using non-covalent bonds to link the molecules to give solubility that chemical cross-linking does not have.A series of urea-based multi-cationic polyarylene-based anion exchange membranes were prepared by grafting the ether-bond-free main chain catalyzed by super acid,and then by accessing different ratios of urea groups,which were characterized and tested to find that PBTA-DQA-35U membrane containing urea groups was characterized to have the highest ionic conductivity of 62.43 m S/cm.Compared with PBTA-DQA membrane(80°C,WU=20.45%,SR=17.67%),PBTA-DQA-25U membrane showed increased water uptake but little change in swelling rate(WU=30.23%,SR=19.36%)due to the hydrophilic urea group providing cation transport sites while hydrogen bonding inhibited the swelling of the membranes.