Microstructural Modulation And Alkaline Resistance Of N-spirocyclic Cations In Anion Exchange Membranes

Alkaline membrane fuel cells have the advantages of fast reaction kinetics and the use of non-precious metal catalysts,but anion exchange membranes as their core components still face scientific problems such as low ion conductivity and susceptibility to degradation in alkaline environments.N-spirocyclic cations have high alkaline stability.N-spirocyclic quaternary cations have high alkali resistance stability,and the construction of hydrophilic/hydrophobic microphase separation is one of the main ways to improve the performance of AEMs through the interrelationship between the cationic groups and the polymer backbone.Therefore,this paper investigates the construction of hydrophilic/hydrophobic microphase separation morphology by means of N-spirocyclic cations induced in an electrostatic field by electrostatic spinning technique,and further investigates the microphase separation structure and alkaline stability of N-spirocyclic cations in rigid poly（biphenyl N-methylpiperidine）backbone chains.The main work and research results are as follows:First,poly（aryl ether ketone）modified with 5/6-membered N-spirocyclic cations was prepared and bead-like nanofibers and defect-free nanofibers with homogeneous morphology were obtained.EDX images confirmed that solvent evaporation drove the migration of N-spirocyclic cations with flexible side chains to the fiber surface during electrostatic spinning.Pore sealing of the nanofiber mats was performed by hot-pressure swelling,which preserved the microscopic morphology of the fibers.Compared to defect-free fibers,beaded nanofibers had a finer fiber diameter distribution,resulting in more nano-separation and size effects.The ionic conductivity of the beaded electrospun membrane B-ASD-PAEK-0.7 was as high as 74 m S cm^-1 at 80℃,much higher than the 48 m S cm^-1 of the cast membrane.At the same time,the three-dimensional channel design enhanced the efficiency and stability of ion transport.The conductivity was maintained above 97%after720 h at 80℃ in 2 mol/L KOH solution.This provides a different design idea for uniaxial electrostatic spinning in ion exchange membranes.A series of N-spirocyclic cation grafted side chains were prepared based on piperazine monomer in order to further investigate the alkaline stability of the N-spirocyclic cation and the microphase separation structure of the N-spirocyclic cation in the rigid main chain poly（biphenyl N-methylpiperidine）.The results showed that the cyclic conformation of the N-spirocyclic cation increased the brittleness of the poly（biphenyl N-methylpiperidine）membrane,and the membrane material with 30%graft ratio had the tensile strength of more than 20 MPa.After introducing the synergistic effect of the main chain piperidine cation,the MDSU-MPBP membrane exhibited the best microphase separation structure and high hydrophilicity,as well as an ionic conductivity of 132.7 m S cm^-1.Alkaline resistance tests show that the DSU cation had the highest alkaline resistance and the MDSU double cation tended to degrade at the C2 and C4 positions.The asymmetrically grafted main chain piperidinium cations exhibited poor chemical stability due to the electron-absorbing effect of the benzene ring.the MDSU-MPBP membrane had the best alkaline resistance,with a conductivity residual of more than 98%after immersion in a 5 M NaOH solution at 80℃ for 240 h.