Carriers Of Tetrazole Grafted-Silane Coupling Agent For Proton Exchange Membrane

Perfluorosulfonated membranes such as Nafion, which its proton conductivity strongly depends on external water or humidity. The catalyst on the electrodes is easily CO poisoned and water and heat from system are difficult to be managed due to low operating temperature (about 80℃). So it attracts much attentions necessary to develop the novel functional proton membrane based on materials bearing with non-water proton carrier proton conductivity themselves. This research is from Henan International Collaboration Project "Design and synthesis of novel proton exchange membranes based on N-heterocycles". (No.104300510009).), which aims at selecting and synthesis a kind of PEM based on N-heterocycles with protogenic conductivity.N-heterocycles, such as imidazole and tetrazole, have protogenic conductivities. First, structures of imidazole and tetrazole ring and proton conductivities from literature reported and electrochemical stability were compared. The results showed that tetrazole has higher proton conductivities than imidazole. Also, the pKa values of some tetrazole derivatives were compared.5-(4-hydroxyphenyl)-1H-tetrazole was appropriate for PEM basic material, which showed good thermal stability until 247℃.Second,5-(4-hydroxyphenyl)-1H-tetrazole was synthesized using 4-cyanophenol and sodium azide as main materials and water as solvent by click 1,3-cycloaddition. The supposed structure was confirmed by FTIR, 1HNMR, Moreover, orthogonal test design and single factor experiments were used optimizing reaction conditions. Optimized conditions were: n(NaN3):n(4-cyanophenol) 1.4:1, reaction at 115℃for 24h, acidifying at 55℃for 90min, the yield was 92.5%. The synthetic process was high yield and environmental benign.Third,5-(4-(3-diethoxymethyl-silyl)-propoxy)phenyl)-1H-tetrazole were formed by condensation using (3-chloropropyl) diethoxymethylsilane as precursor. The structures was supported by FTIR,1HNMR and 13CNMR, the molecular weight distribution was tested by GPC. The optimum reaction conditions were obtained by orthogonal test design and single factor:n (4-cyanophenol):n(KOH): n(3-chloropropyl) diethoxymethylsilane was 1:1.6:1.4,42h. The yield was 69.3%;In the same way,5-(4-(3-trimethoxy-silyl)-propoxy)phenyl)-1H-tetrazole was synthesized.Finally, a novel N-heterocyclic PEM based on tetrazole functional group was obtained by 5-(4-(3-diethoxymethyl-silyl)-propoxy)phenyl)-1H-tetrazole and 5-(4-(3-trimethoxy-silyl)-propoxy)phenyl)-1H-tetrazole were polymerized onto the base membrane-polytetrafluoroethylene through in-situ polymerization. The morphology of surface was examined by SEM and the thermal stability was tested by TG and showed the membrane was thermal stable until 206℃. Proton conductivities were measured by AC impedance from 25-85℃, the higher temperature, the better proton conductivities. It is 6.568×10-4/cm at 85℃.The results showed that it was feasible about the synthetic process for the novel PEM based on tetrazole, the way also provided a certain reference value for the relevant research and development.