One-pot synthesis of inorganic/organic hybrid membranes from organoalkoxysilane, hydroimidazole derivative, and cyclic sulfonic acid ester

Inorganic/organic hybrid membranes for use in fuel cells were synthesized from 3-glycidoxypropyltrimethoxysilane (GPTMS), N-(3-triethoxysilylpropyl)-4,5-dihydroimidazole (NESPHI), and 1,3-propanesultone (PS) through a simple one-pot process. Fourier transform infrared spectroscopy and ¹³C nuclear magnetic resonance (NMR) measurements confirmed the sultone ring-opening reaction and formation of chemical bonds among the starting materials. The ²⁹Si NMR measurements revealed that a siloxane network had formed within the hybrid membranes via the sol–gel process. The thermogravimetric analysis indicated that the synthesized membranes were thermally stable up to 170 °C. The conductivity of the membranes at low levels of relative humidity (RH) was improved by the addition of NESPHI. The best cell performance at intermediate temperatures and low RHs was achieved by the membrane electrode assembly using the NESPHI/GPTMS/PS = 1:3:4 hybrid membrane with a catalyst ink consisting of Nafion and the hybrid solution at a 1:1 ratio. At 120 °C and 53 % RH, the power density of the NESPHI/GPTMS/PS = 1:3:4 membrane was 6.6 mW/cm².