Sol–gel synthesis of proton conductive tetrazole functional silane networks

In this work, 3-glycidoxypropyl trimethoxy silane (GPTMS) was functionalized with 5-aminotetrazole (ATet) via ring opening of the epoxide ring and then sol–gel polymerization was performed to produce tetrazole containing silane networks abbreviated as Si-ATet. In addition during sol–gel process trifluoromethane sulfonic acid (TA) was introduced into the matrix with several stoichometric ratios (TA/ATet = 0.5 and 1) to produce Si-ATetTA0.5 and Si-ATetTA1 polymer electrolytes. Fourier transform infrared spectroscopy (FT-IR) confirmed the tethering of the ATet into the silane compound and the sol–gel reaction, thermogravimetry analysis (TGA) showed that the membranes are thermally stable up to 180 °C. Differential scanning calorimeter (DSC) verified the softening effect of the dopant and the homogeneity of the samples. The proton conductivity of these novel silane networks was studied by dielectric–impedance spectroscopy. Although proton conductivity of these membrane electrolytes depends on the doping level, the membrane without dopant produced a proton conductivity of 10−4 S/cm at 150 °C in dry state. The conductivity isotherms show Vogel–Tamman–Fulcher (VTF) behavior which implies the coupling of the charge carriers with the segmental motion of the polymer chains. A maximum proton conductivity of 1.8 × 10−3 S/cm was obtained for the sample Si-ATetTA1 in anhydrous condition.

►Inorganic–organic hybrid materials were produced via sol–gel method. ►5-Aminotetrazole was immobilized into silane matrix with flexible chains. ►Transparent, free standing and high proton conductive membranes were obtained.