Preparation And Research Of Ether-Bond-Free Polyaryl Anion Exchange Membrane

With the over-exploitation and use of fossil energy,human beings are facing the dilemma of energy depletion and environmental pollution.With the global goal of"carbon peaking and carbon neutrality",the fuel cell technology using hydrogen as fuel has attracted much attention.Proton exchange membrane fuel cells(PEMFC)have already been commercialized,but they require platinum as a catalyst,which greatly increases the cost of PEMFC and limits its application.In contrast,anion exchange membrane fuel cell(AEMFC)is considered as an alternative to PEMFC due to its operation in alkaline environment,faster redox reaction rate at the electrodes,and the possibility of using non-precious metal catalysts such as Ni,Co,and Ag,which reduces the cost of fuel cells.However,the core component of AEMFC,anion exchange membrane(AEM),is still facing the problem of low conductivity and"trade-off"between conductivity and stability.To address this problem,we prepared AEM with dual cation transport sites and self-aggregating cation side chain structures by copolymerization and comb grafting strategies,as follows:We selected an ether-bond-free main chain copolymerized by biphenyl,isatin and 1-methyl-4-piperidone and piperidine cationic group as the main material of AEM to increase the base stability of AEM.In addition,the main side chain double cation site structure was designed to increase the OH~-transport site,and the long hydrophobic alkyl chain created a hydrophobic and hydrophilic microphase separation structure to improve the ion transport efficiency of AEM,thus enhancing the ion conductivity of the membrane while ensuring the dimensional stability of AEM.A series of side-chain type AEM were prepared by changing the grafting rate of long alkyl cation side chains.it was observed under TEM that the long alkyl side chain structure induced the formation of phase separation structure in the membrane to some extent,and the phase separation structure was first obvious and then blurred with the increase of cation side chain grafting rate,and the conductivity results were also consistent,among which the ion conductivity of PBP-54-IS-90 membrane reached a maximum of 85.53 m S/cm at 80℃.The rigid backbone without ether bond makes the tensile strength of the membrane between 19.52 MPa and 34.61 MPa,and the thermal decomposition temperature is located above 270℃,which is quite outstanding in mechanical properties and thermal stability.In addition,the OH~-conductivity of the membranes were all maintained above 68.42%of the original after soaking in 1 M KOH for 1000 h at 80℃.We then further optimized the side chain structure by replacing the previous long alkyl carbon chain with an electronegative alkoxy chain and using the previous poly(biphenyl-isatin)piperidine as the main chain to synthesize the AEM with cationic self-aggregation,which utilizes the dipole interaction between the electronegative side chain and cation to build a better hydrophobic and hydrophilic microphase separation structure to improve the ionic conductivity of the membrane.Meanwhile,2-bromoethanol was added for complete grafting to reduce the OH~-attack sites and form hydrogen bonds with water to further improve the base stability of AEM.TEM tests showed that the self-aggregating cationic side chain type AEM had a more obvious phase separation structure and its conductivity was further broken through as a result,with PBP-54-IS-[OPD-100-OH-0]reached a maximum of 100.62 m S/cm at 80℃.The alkali stability was also further improved,and the ionic conductivity of all membranes could still be maintained above 88.24%of the original value after immersion in 1 M KOH for 1000 h at 80℃,which provided a feasible new direction for the study of preparing high-performance AEM.