Preparation,Characterization And Application Of Anion Exchange Membrane Based On Phosphonium Cation Brush Copolymers

As an important part of anion exchange membrane fuel cells(AEMFCs),anion exchange membranes(AEMs)are responsible for conducting charged hydroxide ions and forming a current loop inside the battery.As far as the current research status is concerned,low conductivity and insufficient alkali resistance hinder the further development of AEMs.Therefore,the development of new AEMs is of great significance for reducing battery costs and achieving efficient and clean conversion of energy.In this study,first synthesized the phosphonium-based cationic brush copolymer SMP with tetraphenylphosphonium(TP)as the cationic side chain and styrene-maleic anhydride alternating copolymer(SMA)as the main chain;Compatibility of PVDF blending system;SMP/PVDF blended anion exchange membranes were prepared by blending technology and phase inversion method,and the structure,microscopic morphology,crystallization,mechanical properties,and ion conduction of blended anion exchange membranes were studied.The specific research content is as follows:1.Designed and synthesized phosphonium-based cationic brush copolymer SMP.First,tetraphenylphosphonium amine(TPP)is synthesized by coupling reaction of tris(4-methoxyphenyl)phosphine and 4-bromoacetanilide followed by deacetylation,and then through amidation and cyclic imidization reactions TPP is grafted onto the backbone of SMA alternating copolymer to prepare phosphonium-based cationic brush copolymer SMP.Characterize the structure and performance of SMP: use FT-IR,NMR and XPS to determine the structure of phosphonium cation and brush graft copolymer SMP.The result of XRD and DSC of copelomer were as follow.The crystalline morphology and aggregate structure of the copolymer were studied by DSC.XRD showed that the crystallinity of SMP was 71.04%.DSC showed that SMP had a glass transition phenomenon at 430?.The thermal stability of SMP was studied by SMP was at 150?.It can remain stable within and has the potential to be used in AEMs.2.Co-solvent method,EDS and DSC are used to study the compatibility of the blend system formed by SMP/PVDF.The results show that the solution with uniform macro mixing is formed in DMAC at 70? by SMP and PVDF;EDS showed that the elements in SMP/PVDF blends were distributed intensively and evenly;DSC showed that the glass transition phenomenon appeared at 250? and only one glass transition temperature appeared after SMP was added.All of the above studies can show that SMP and PVDF blend system have good compatibility,which provides support for the subsequent blend membrane.3.SMP/PVDF blend anion exchange membranes were prepared by blending technology and phase inversion method.The phosphonium cation in the membrane was determined by FT-IR;The surface and internal structures of the blend membranes were characterized by SEM;XRD was used to characterize the crystalline state of the blend membranes.The results showed that there were two kinds of phase structures in the blend membranes: crystalline region and amorphous region.The content of SMP was 30%,and the crystallinity of the blend films was 75.31%;The thermal stability of the blend membrane was studied by TGA.The thermal stability of the prepared SMP/PVDF membrane was above 200?,which could meet the requirements of alkaline fuel cell;The ion exchange capacity(IEC)of SMP/PVDF blend membrane was measured by titration.With the increase of SMP content,IEC increased gradually,reaching the highest value of 1.58 mmol/g.the water absorption of SMP/PVDF blend membrane was 79%,and the swelling ratio of the membrane was less than 41%.The tensile test shows that the tensile strength of SMP/PVDF blend film is in the range of2.2-5.5MPa,and the elongation at break is in the range of 2.5%-14%,which is acceptable for AEMs.The conductivity of the SMP/PVDF blended anion exchange membrane was measured on an electrochemical workstation using the AC impedance method.The results show that,on the one hand,the increase of IEC increases the cation density,and the conductivity of the membrane increases with the increase of IEC.At 30?,the SMP content is 30% and the conductivity is 29.8m S/cm;on the other hand,The phosphonium-based cationic brush copolymer forms a more complete ion exchange channel through microphase separation at high temperature.The continuous ion region ensures higher conductivity.The conductivity of the SMP membrane can reach49.3 at 80?m S/cm.The simulation analysis shows that the relationship between the conductivity and temperature of the SMP/PVDF anion exchange membrane conforms to the Arrhenius formula,and the ion migration activation energy is 14.313 k J/mol.At room temperature,immersed in 1mol/L Na OH solution and blended with anion exchange membrane for 10 days,the conductivity loss rate is 30%.