Structure Design And Performance Research Of Membrane Materials To Improve Anion Conductivity

The polymer electrolyte fuel cells(PEFCs)convert the chemical energy in the fuel into electrical energy through electrochemical equipment.They have attracted much attention because of its high efficiency,fast start-up,clean and environmentally friendly,easy disassembly and assembly,and abundant fuel sources.Anion exchange membrane fuel cells(AEMFCs),which are a branch of PEFCs,can use non-precious metal catalysts to reduce costs,and have the advantages of diverse fuel options and low fuel crossover,so they have gradually become a research hotspot in recent years.As the main component of AEMFCs,anion exchange membranes(AEMs)directly determine the performance and durability of AEMFCs.Nowadays,AEMs have been developed rapidly,but the low conductivity and alkaline stability are still the main bottlenecks restricting their practical application.The key to the development of high-performance AEMs lies in the design of the molecular structure of AEMs.The construction of ion channels is a generally accepted method to increase the ion transport rate.Therefore,starting from the concept that material performance depends on its structure,and based on the superacid-catalyzed polyhydroxyalkylation reaction,side-chain type,cross-linked type,and microporous type AEMs were designed and fabricated,for constructing ion channels in the membrane and preparing AEMs with high-efficiency conductivity.Moreover,the relationship between structure-morphology-performance was explored.It is expected to build new high-performance AEMs so as to satisfy the application requirements of AEMFCs.Firstly,side-chain poly(aryl ether ketone)anion exchange membranes(QPAEK/PPAEK/GPAEK)were constructed based on the reaction of the isatin derivative and aryl ether ketone monomer.The long flexible side chains can increase the activity of suspended cations,which is conducive to the construction of ion transport channels.Among them,microphase separation was observed in QPAEK and PPAEK AEMs,and they had comparable OH-conductivity(44.5 and 45.8 mS/cm at 30?,respectively).However,the type of cation also has influence on the construction of ion transport channels.For example,GPAEK membrane with hydrophobic cationic(pentaethylguanidinium)has no obvious phase separation and has very low OH-conductivity(6.1-11.8 mS/cm)in the range of 30-80?.At the same time,the membrane electrodes assembled by QPAEK and PPAEK were tested for H2/O2 single cell.The results show that the peak power density at 60? is 69 mW/cm2 and 92 mW/cm2 respectively,which proves the feasibility of QPAEK and PPAEK in the field of fuel cells.In addition,the prepared QPAEK,PPAEK and GPAEK have good alkaline stability,thermal stability,two-dimensional stability and maintain instact in 1 M NaOH aqueous solution at 60? for 600 h.Based on the cross-linking strategy,self-standing anion exchange membranes with dibenzo-18-crown-6 and piperidinium salt were designed and synthesized.The crown ether component has hydrophilic oxygen-rich ring and can coordinate with alkaline metal ions,which plays a positive role in ion transport.In this part,the relationship between the content of crosslinking agent and the performance of the membrane was discussed.It was found that the fully crosslinked QPCEPip-100%AEM has the highest water uptake and OH-conductivity(58 mS/cm at 30?),and lowest swelling rate(<25%),which reveals the importance of crosslinking for the two-dimensional stability of the membrane.At the same time,QPCEPip-100%AEM shows higher performance than commercial FAA-3-50 when applied to single cell test.The peak power density at 60? is 247.4 mW/cm2.In the work of the fifth chapter,we designed the microporous AEMs based on the spirobiindane structure.The polymer with high molecular weight(Mn=95-212 kDa)was obtained from the high polymerization activity of spirobiindane monomer(SBI).The content of SBI in the main chain was adjusted to explore the influence of SBI on the performance of AEMs.It was found that the rigid-twisted structure of SBI was conducive to the construction of developed ion channels,reducing the resistance of ion transport in the membrane,thus improving the conductivity.The conductivity of QP(SBI/AES)-1 AEM is up to 85 mS/cm at 30?.When used in single cell test,QP(SBI/AES)-0.5 with SBI segment shows a peak power density of 437 mW/cm2,which is 115%higher than QP(SBI/AES)-0 without SBI segment.This shows that the participation of this microporous structure will not lead to serious fuel crossover,but can improve the performance of fuel cells.