Design And Preparation Of Anion Exchange Membranes For Alkaline Fuel Cells With Enhanced Hydroxide Transport

Recently,polymer electrolyte membrane fuel cells have attracted many researchers due to their advantages of low operation temperature,high power density and environmentally friendly properties.As a kind of clean energy,polymer electrolyte membrane fuel cells can be categorized into two types:proton exchange membrane fuel cells(PEMFCs)and alkaline anion exchange membrane fuel cells(AAEMFCs).PEMFCs have developed fast since the discovery of commercial Nafion membranes.However,the expensive costs of Nafion membranes hinder the large-scale promotion.Thus,AAEMFCs have become new trends because of their superiorities including improved kinetics of the electrode reactions,broad resource of catalysts based on nonprecious metals and less fuel leakage.As one of the most important components of AAEMFCs,AEMs can decide the properties,lifetime and efficiency of fuel cells.Qualified AEMs are required to own high hydroxide ions conduction,enough mechanical strength and good chemical stabilities especially in alkaline conditions.Current studies have shown that there is a close relationship between the microscopic morphology of membranes and their properties.Ideal micro-phase separation morphology can provide channels for hydroxide ions and accelerate their transport.In addition,considering the transport mechanism of hydroxide in the membranes,we recognize that the role of water molecules is essential.In the future development of high temperature AAEMFCs,the evaporation of water in the membrane will become one of the main reasons for the decline of membrane performance.Therefore,the development of AEMs with good water retention ability is also an important method to promote the development of AAEMFCs.Based on this,the main research contents of this topic are as follows:(1)In this project,we employed ABFPPO to act as a main chain.Then we prepared comb-shaped copolymers by grafting quaternary ammonium cations to gain functional side chains.Under the premise of similar ion exchange capacity,we can synthesize two kinds of comb-shaped polymers by controlling the grafting length and grafting ratio.Comb-shaped AEMs possess high graft density and low graft length,which could induce the formation of desirable phase separation morphologies.Therefore,the hydroxide conductive properties of comb-shaped AEMs are expected to be much higher than other reported AEMs.Combined with coarse-grained molecular dynamics simulation,we can predict the microscopic morphology of polymer membranes from the molecular level.This can be applied to guide the structural design of AEMs.(2)Referring to the superior water retention process of cactus in nature,we synthesized similar hollow porous microcapsules structures(HPMCs)and introduced them into the common quaternary polyphenylene ether anion exchange membrane(QPPO).The conductivity of the QPPO-HPMCs membrane we synthesized was tested at low relative humidity to see if it worked.Besides,we tested the performance when it was used in an actual H2-O2 fuel cells test environment.The above experiments proved that HPMCs had excellent water retention capacity.This work provides a widely applicable strategy for the development of anion exchange membranes.