Poly(Isatin Biphenylene)-based Alkali-resistant Anion Exchange Membranes:Preparation And Performance Studies

A fuel cell is a power device that provides electrical energy through an electrochemical reaction.At present,the anion exchange membrane fuel cell（AEMFC）has received the most attention.Anion exchange membrane（AEM）is one of the core components of the battery,which plays the role of separating fuel and oxidant,transferring ions and water molecules,etc.Therefore,an ideal AEMs must have balanced dimensional stability,ion conductivity and chemical stability,but the membrane materials synthesized at present all lack long-term alkaline stability,which is one of the necessary technical foundations for the long-term stable operation of batteries.The main reasons for the decomposition of the membrane in an alkaline environment are the chain scission of the polymer backbone and the decomposition of the cationic functional groups.In this paper,a variety of AEMs with high alkali resistance were prepared by selecting more stable polymer backbones and cations and dynamically protecting cations by macrocyclic molecules for the above reasons.The main work and research results are as follows:First,the effect of organometallic cation-functionalized poly（isatin biphenylene）on improving membrane alkali stability was explored.A side-chain AEM with poly（isatin biphenylene）polymer as the main chain and organometallic cation-[Cp-Fe-toluene]PF₆ as the ion transport group was designed and prepared,and the two were connected by three different long side chains.The relationship between the microphase separation structure size and ionic conductivity of the membrane was studied by TEM,SAXS and electrochemical workstation:long side chains can promote the formation of phase separation structures,and the phase separation size corresponding to the side chain length follows the following rules:butyl>amyl>propyl.The PIB-CB-[Cp-Fe-toluene]membrane composed of butyl side chains showed the highest ionic conductivity performance of 63.25 m S·cm^-1 at 80°C.In addition,after 1000 h of alkali stability testing in 1 M KOH solution at 60°C,the hydroxide conductivity at 80°C can still reach 81.4%of the pre-test performance.Subsequently,the study on improving the alkali stability of membranes by rotaxane-functionalized polyarylindole was explored and continued to use the chemically stable poly（isatin biphenylene）polymer as the polymer backbone,the pseudorotaxane molecules formed byα-cyclodextrin and polyviologen compounds through the host-guest coordination as the polycationic side chain,and prepared the cross-linked AEM with host-guest structure through the cross-linking reaction.By controlling the cross-linking degree of the membrane,it is found that the comprehensive performance of the membrane is the best when the cross-linking degree reaches 7%,and the hydroxide conductivity of Pri¹⁰-PIB with host-guest structure at 80°C is 114 m S·cm^-1,the swelling rate is 13.7%,and the tensile strength reaches32.92 MPa.At the same time,the alkali stability test showed that the hydroxide conductivity of the Pri^x-PIB membrane with host-guest structure can still reach more than 90%of the performance before the test after being tested in 5 M KOH at 80°C for 1000 h,while The hydroxide conductivity of Pi^x-PIB without host-guest structure is reduced to 70%.