Structure Configuration And Performance Study Of Polyaryl Based Anion Exchange Membrane For Alkaline Membrane Fuel Cell

With the development of new energy industry,fuel cell stands out in the field of new energy due to its advantages of high efficiency,environmental protection and sustainability.Among fuel cells,polymer electrolyte fuel cells have been extensively developed in aerospace,automobiles,mobile power sources,etc.According to the types of ions transported,polymer electrolyte fuel cells are divided into PEMFC and AEMFC.PEMFC has many applications,but its high cost limits its commercialization process.Compared with PEMFC,AEMFC has a higher oxygen reduction reaction kinetics.It can use non-noble metal catalysts to greatly reduce costs.Therefore,it has received extensive attention and has been considered as a next-generation fuel cell technology that can replace PEMFC.Anion exchange membrane(AEM)is one of the important parts of AEMFC,It is used to transport ions and isolate cathode and anode gases.Its performance is directly related to the power generation efficiency and service life of the fuel cell.Thus,the development of high-performance anion exchange membranes is of great significance to the development of AEMFC.However,AEM are still facing problems such as low ion conductivity,poor alkali resistance and insufficient mechanical stability,which have become a bottleneck restricting the development of AEMFC.In recent years,the preparation of composite membranes by introducing inorganic materials into the membranes and the design of membrane backbone and cationic groups from the molecular structure to construct phase separation within the membrane are two effective methods to improve membrane performance.Therefore,in order to solve the above problems and improve the overall performance of the membrane,this paper starts from the two aspects of homogeneous membrane and heterogeneous membrane,and designs and synthesizes a variety of polyaryl anion exchange membranes through inorganic-organic composite,copolymerization,cross-linking and other strategies.In-depth study of the structure-activity relationship of the membrane,the main research content is as follows:(1)We synthesized cationic group-modified graphene oxide ASU-GO as an inorganic ion transport conductor and prepared piperidine-grafted polyphenylene ether as an organic polymer.Based on the organic-inorganic composite strategy,a layered organic-inorganic composite membrane was developed using electrostatic spraying method.The prepared ASU-GO/PIPPO composite membrane possesses strong moisture retention,which ensures ion conductivity under low humidity.In addition,due to the protection of the organic polymer layer,the swelling of the composite film is less than 30%even at high temperatures,showing strong dimensional stability.Compared with the graphene oxide before modification,the modified ASU-GO stack structure is significantly reduced,and it provides more ion transport sites and improves ion conductivity.Compared with the GO/PIPPO,the ionic conductivity of ASU-GO/PIPPO is increased by nearly three times;after immersing in 1M NaOH at 80? for 700 hours,its ionic conductivity is only degraded by 10%,showing high alkaline stabiltiy.(2)Hydrotalcite(LDH)with better alkali resistance and ion conductivity is selected as an inorganic material and surface modification is performed to prepare ASU-LDH.The polyphenylene ether polymer grafted with multications was synthesized to further improve its ionic conductivity.A three-layer structure ASU-LDH/TCPPO organic-inorganic composite membrane was prepared by electrostatic spraying,and the effect of the thickness of the LDH layer on the performance of the composite membrane was studied.Due to the ion transmission ability between and outside the ASU-LDH layer,the ion conductivity of the ASU-LDH/TCPPO composite membrane is increased by 56%compared to the pure membrane TCPPO,reaching 113 mS/cm,and has a more excellent dimensional stability,oxidation resistance and alkali resistance.(3)Based on the super acid-catalyzed polymerization reaction,an ether-free poly(biphenylbromohexyl indole)(PPHIN)skeleton was prepared,and combined with the strategy of "spacer side chain" and "extended chain",the grafted ends with double cations with different length alkyl chains.Induces the formation of microphase separation in the membrane,improves the ion conductivity and alkali resistance of the membrane,and explores the influence of branched chains of different lengths into the microphase separation structure and membrane performance.The microphase separation structure of the membrane and the performance of the membrane with branched chains of different lengths have been explored.This comb-shaped ion string membrane has an obvious microscopic phase separation structure.PPHIN-N1C shows the highest hydroxide ion conductivity of 136 mS/cm at 80?.The steric hindrance and high electron density of the introduced alkyl chain inhibit the Hoffman elimination of cationic groups,thereby improving the alkaline stability of AEM.After immersing in 2 M NaOH for 1000 hours,the ionic conductivity of PPHIN-N8C only decreased by 13%.(4)Based on the covalent crosslinking strategy,in order to improve the dimensional stability of the membrane,a polybiphenyl-methylisatinbromohexylisatin block copolymer(PPMHIN)was synthesized,and hydrophobic crosslinking was grafted onto the backbone(Cx)base and multi-cation string(TQA),a series of hydrophobic cross-linked anion exchange membranes(PPMHIN-TQA-Cx)with different cross-linking degrees were prepared.The block copolymer framework structure of this series of membranes promotes the formation of the microphase separation structure in the membrane,and its ion conductivity at 80? reach up to 85 mS/cm.Under the premise of ensuring conductivity,the hydrophobic cross-linked structure significantly reduces the swelling degree of the film and improves the dimensional stability of the membrane.The swelling of the PPMHIN-TQA-C15 at high temperature is only 7%.(5)In order to balance the ion conductivity,alkali resistance and dimensional stability of the membrane,it also seeks a simpler and more efficient synthetic method that is beneficial to scale-up production.Using biphenyl,piperidone and bromohexylisatin as monomers,ether-free polybiphenylpiperidine-bromohexylisatin was synthesized as the polymer backbone(BPPIN).Cyclic piperidine is used as the cationic group,combined with a partial cross-linking(QCx)strategy,to improve the alkali resistance and dimensional stability of the membrane.The synthesis method is simple,with fewer steps,and the prepared BPPIN-QCx cross-linked membrane has higher conductivity.The ionic conductivity of this series of membranes at 80? is up to 111 mS/cm,the swelling of the membrane is less than 25%,the tensile strength reaches 52 MPa,and the conductivity is only degraded by 15.4%after the 1400 h alkali resistance test.This series of membranes have high ionic conductivity and dimensional stability,while showing excellent alkali resistance.