Preparation And Study Of Poly(Arylene Piperidinium) Anion Exchange Membranes

As more attention was paid to environmental pollution and energy shortage,hydrogen energy as a clean energy has become one of the important research directions.Polymer electrolyte membrane fuel cells are a new generation of fuel cells,which act as high-efficiency hydrogen energy conversion devices.According to the type of polyelectrolyte membrane,it can be divided into proton exchange membrane fuel cells(PEMFCs)and alkaline exchange membrane fuel cells(AEMFCs).PEMFCs are currently available for commercialization,but their scale of commercialization is limited,due to their expensive separators(Nafion membranes based on fluoropolymers)and precious metal catalysts.In contrast,AEMFC can use membranes based on non-fluorinated polymer and non-precious metal catalysts.So it become a technology to control the cost of fuel cells,and has developed rapidly in recent years.Anion exchange membrane(AEM)is one of the core components of AEMFC,but its performance has not yet met the standards for practical applications,which also become the main reason for limiting the commercialization of AEMFC.At present,the research direction of AEM is mainly based on polyarylether-based,polyolefin-based polymers and common quaternary ammonium and quaternary phosphorus cationic groups,and the performance of the membranes are improved through a series of modification methods.However,the improvement is often limited,and most researches cannot solve the problem fundamentally.AEM still has the problems of insufficient ionic conductivity and alkali resistance,which is due to the intrinsic problems of OH-ions moving slower than H+ ions,and quaternary ammonium cation groups being prone to side reactions such as Huffman elimination under alkaline conditions.Therefore,this article abandoned the traditional polymer,designed and modified a new type of polymer without ether bond from the perspective of molecular structure design,which is hoping to improve the overall performance.The specific researches are as follows1.Preparation and study of multi-cations-crosslinked poly(biphenyl piperidium)-based anion exchange membranesA novel poly(biphenyl piperidium)backbone without ether bonds was prepared by a strong acid-catalyzed polymerization method.A multi-cations cross-linking agent containing alkyl bromide at both ends was prepared so that it can self-crosslink with the piperidine ring of the main chain.The influence of the degree of cross-linking on membrane properties was explored.The cross-linked structure plays a role in controlling the dimensional stability,and promoting the conduction of OH-,making the conductivity up to 155 mS/cm.Due to the large steric hindrance of the crosslinked network,it can prevent the nucleophilic attack of OH-and improve the alkali resistance of the membrane2.Studies on the structure-effect relationship of poly(arylene piperidium)-based anion exchange membranes with different configurationsIn order to further control the water absorption of the membrane,three kind of poly(arylene piperidium)were prepared by using p-terphenyl,m-terphenyl and a mixture of biphenyl-terphenyl as monomers.By using the optimal crosslinking degree explored by the above system,crosslinked membranes based on three polymers were prepared.Overall,due to the lower theoretical IEC of terphenyl polymers,water absorption and swelling ratio of the three membranes were controlled(WU<70%,SR<20%).However,due to the different spatial configurations of their main chains,they showed different results in terms of ion conductivity and water absorption.After testing and configuration simulation,it was found that the membrane based on m-terphenyl was folded and twisted in its main chain space,making it easier to form ion clusters and absorb water,which was beneficial to OH-conduction.3.Preparation and study of poly(m-terphenyl piperidium)anion exchange membranes grafting with multi-cations side chainAlthough the dimensional stability of membrane was controlled in the previous chapter,the ion conductivity was sacrificed.In order to balance the two properties,the structure of "densely grafting" side chain structure away from the backbone was chosen.M-terphenyl monomer with configuration advantages was used and trifluoroacetophenone was introduced for block copolymerization,which aimed to adjust the IEC and improve the mechanical properties of the polymer.The conductivity of the prepared membrane was up to 164.12 mS/cm.The results show that when the grafting ratio is 15%,the degree of the "dense grafting" side chain can balance the water absorption and ionic conductivity.