High temperature proton exchange membranes based on triazoles attached onto SBA-15 type mesoporous silica

Triazole shows rather high proton conductivity under anhydrous condition and high temperature, where the proton conduction arises from the transfer of protons between neighboring protonated and unprotonated guest molecules, i.e., intermolecular proton transfer between adjacent triazole groups. When triazole is incorporated into a polymeric matrix for proton exchange membranes, it may leach out gradually because of no bonds formed between the triazole and the polymeric matrix, leading to the decrease in the proton conductivity. Therefore, a proton conductive pathway is constructed through mesoporous silica SBA-15 by reacting benzotriazole-5-carboxylic acid with the surface hydroxide groups. SBA-15 has hydroxyl groups inside pores. Thus, triazole groups were attached to the inside of the nanopores of SBA-15, which was subsequently dispersed in Nafion membrane. The proton exchange membrane showed the proton conductivity of 8.52 × 10−4 S/cm at low humidity of ∼10% and 140 °C. It also exhibited a thermal stability up to 200 °C. Therefore it was concluded that the new proton exchange membrane showed no leaching problem, by rather low proton conductivity, which should be increased further for practical applications for high temperature fuel cells.