Preparation And Performance Research Of Phosphonic Acid Functionalized Siloxane/SPEEK Proton Exchange Membrane

As a new way of energy source,proton exchange membrane fuel cell?PEMFC?has been widely studied by researchers for its low pollution and high energy conversion rate.As the core component of proton exchange membrane fuel cell,the performance of proton exchange membrane has a direct influence on PEMFC as a whole.After years of research,the main direction is to improve the operating temperature of PEM,because the rising operating temperature not only reduce the cost of PEMFC operation effectively,and avoid the possible poisoning of the catalyst at low temperature and gas permeability.Phosphonic acid is widely used in the study of high temperature and low humidity PEM because of its unique amphoteric properties.Such membranes exhibit good proton conductivity at high temperatures,but there are still some problems to be solved,such as low temperature conductivity,poor membrane forming and mechanical properties.Moreover,high temperature membranes need a certain time to run normally at start-up in low temperature conditions.Therefore,this paper hopes to prepare a PEM which can operate normally at high and low temperatures.In this paper,the amino trimethylene phosphonic acid?ATMP?was chemically bonded to the 2-?3,4 cyclohexyl?ethyl trimethoxy silane?EHTMS?in the form of covalent bond by epoxy ring opening reaction and compound with sulfonated polyether ether ketone?SPEEK?.And the self-hydrolytic crosslinking reaction of EHTMS was used to form a continuous Si-O-Si crosslinking network in the SPEEK matrix.Then,the effect of free phosphonic acid was eliminated.According to the proportion of ATMP,EHTMS and SPEEK components in samples,a series of AES-X membrane materials were prepared,and their structural characterization and performance analysis were carried out at the same time.FTIR test results showed that the epoxy ring opening reaction of ATMP and EHTMS was carried out,and Si-O-Si cross-linking structure formed successfully.The AES-X series membrane samples are thermally stable within the range of 250°C,which can meet the requirements of high temperature and low humidity PEMFC.Meanwhile,the good membrane forming property of SPEEK effectively improved the poor membrane forming ability of phosphonic acid functionalized siloxane,and the obtained samples has good flexibility and mechanical strength.By introducing the hydrophilic materials such as phosphonic acid and the siloxane crosslinking structure,the water absorption of the membrane improved,meanwhile,the swelling of the membrane was effectively controlled,it also provide more proton transfer sites which facilitated proton transfer.thus,the conductivity and IEC value of AES-3 and AES-4membrane exceeded SPEEK in 80°C water conditions.In particular,the proton conductivity of AES-4 samples reached 0.114Scm^-1 and 0.0463Scm^-1 at 80°C?100%RH and 140°C?20%RH,respectively,which could meet the application requirement of PEMFC at high and low temperature.