Study On The Preparation And Performace Of Proton Exchange Membrane Made From Polysiloxane Based On Nitrogenous Polyphosphoric Acid Modified By PVDF-HFP

Acid-base properties and outstanding water performance under the relatively dry condition compared to other proton carrier made the phosphoric acid become the new generation of proton conduction medium gradually. Phosphoric acid functionalized polymers as membranes in the fuel cells have been reported largely, however, the low hydrolysis resistance of phosphate groups and proton conductivity hindered the development of the technology, if we can solve these two problems, that will greatly promote the development of proton exchange membrane fuel cell.In this paper, we use the epoxycyclohexylethyltrimethoxysilane(EHTMS), amino trimethylene phosphonic acid(ATMP) and poly(vinylidene fluoridehexafluoropropylene(PVDF-HFP) as raw materials, dimethyl sulfoxide(DMSO) as solvent, using the sol-gel process to synthesis the proton exchange membrane. In this process, we expect to use the siloxane ring opening reaction between epoxy groups and hydroxyl phosphorus to make phosphate chemically bonded to siloxane, space steric effect of six-member ring in the siloxane can prevent the C-O-P bond hydrolysis. Atoms F in PVDF-HFP molecular has strong electron-withdrawing ability, when adding the PVDF-HFP into the proton membrane, in addition to the original continuous hydrogen bond network of proton conduction in proton membrane, F atoms in PVDF-HFP also can promote the proton conduction. So we prepared two groups of different ratio of proton membrane, one group is EHTMS/ATMP proton membrane, another is PVDF-HFP modified EHTMS/ATMP proton membrane, by means of series of tests to explore what influences on the proton membrane when andding the PVDF-HFP into the proton membrane.FT-IR and XRD analysis showed that EHTMS has successfully conduct the ring opening reaction with ATMP, ATMP connected with EHTMS by chemical bonds, which improved the stability of ATMP in membrane, and at the same time, the siloxane in EHTMS successfully hydrolyzed and formed the Si-O-Si network structure. TG and DSC thermal analysis showed that the two groups of proton membranes show good thermal stability within 200℃, the addition of PVDF-HFP didn’t diminish the property of thermal stability of membranes, meeting the using demand of the proton exchange membrane at high temperature. Morphology analysis showed that there are no apparent phase separation phenomenon in the surface of PVDF-HFP modifing proton membrane, this indicated that PVDF HFP has a good consistency with proton membrane, the cross section analysis found that the addition of PVDF-HFP may make the space of siloxane become larger, just like the effect of swelling, this would produce more structure of microporous in the proton membrane, promoting the ability of water retention. The test of hydrolysis resistance showed that the addition of PVDF-HFP improved the hydrolysis resistance of proton membrane and also the water absorption at the same time, but lowered the swelling of the proton membrane. XPS analysis shows that two groups of proton membranes were not completely homogeneous system. By means of proton conductivity tests, we found that below 120℃, PVDF-HFP modified membranes’ conductivity were lower than unmodified proton membranes’ conductivity, however, when above the 120℃, the condition ie reversed, this indicated that at high temperature, the introduction of the PVDF-HFP were favorable for the formation of continuous hydrogen bonds in the system of proton membrane, the proton transferred through the restructuring of hydrogen bonds.