The New Proton Exchange Membrane Based On 5-Substituted Tetrazole Functional Group

One of the commercial membranes is Nafion (Du Pont) which is applied in Proton Exchange Membrane Fuel Cells (PEMFCs) due to its high proton conductivity, good mechanical strength and chemical stability. But the practical application of Nafion is limited because of its conductivity strongly depending on water and low operating temperature (about 80℃) which cause the catalyst easily CO poisoned, water and heat from system difficult to be managed. So, it is necessary to develop the novel PEM with good electrochemical stability and high working temperature. As the Henan International Collaboration Project (No.104300510009), aiming at design and synthesis novel PEM, 5-substituted tetrazole molecule was one of the options, for it bears nitrogen-rich conjugate ring and protogenic proton.First,5-(4-Hydroxyphenyl)-1H-tetrazole (I) was synthesised using 4-cyanophenol and sodium azide as main materials by click chemistry. The influence of variables in cycloaddition were examined by orthogonal test design and single factor experiment. The optimum reaction conditions were obtained, the yield of I was 88.73% nder n(4-cyanophenol):n (NaN3)= 1:1.4, reflux at 130℃for 24h, acidifying at 50℃for 1.5h. The structure and properties of I were characterized by FTIR, NMR, and DSC.Second, as the polymer precursor of PEM,5-(4-(3-dimethoxy methyl silane propoxy) phenyl)-1Htetrazole (II) was synthesized through graft condensation used I as the starting materials. The structure ofⅡwas characterized by FTIR, NMR and DSC. At last, the influence of variables in the yield of II was examined through single factor and orthogonal test.design The optimum reaction conditions of synthesisⅡwere as followings:n (I):n ((3-chloropropyl)dimethoxy(methyl)silane)= 1:1.1,70℃,46h. Then the yield was 80.46%.Finally, through the sol-gel reaction, productⅡwere in-situ polymerized onto the base membrane-polytetrafluoroethylene and a novel N-heterocyclic PEM based on 5-substituted tetrazole functional group was obtained. The morphology and fracture surface morphology were determinated by SEM and the thermal stability was tested by DSC.The results showed that the synthetic process of the novel PEM based 5-substituted tetrazole functional group by click cycloaddition, graft condensation and the in-situ polymerization was feasible.