Preparation and proton conductivity of composite SiO2/Poly (2-hydroxyethyl methacrylate) gel membranes

A series of organic/inorganic composite materials based on silica/poly(2-hydroxyethyl methacrylate) (PHEMA), to be used as proton-conducting membranes, have been synthesized through sol-gel processes. The PHEMA polymer was thermally cross-linked by silica gel via the esterification reaction between OH-groups of PHEMA and SiOH-groups of silica and/or by the formation of hydrogen bonds between functional groups of PHEMA and SiOH-groups. The membranes were characterized in terms of equilibrium swelling in water, sulfuric acid and ferric sulfate solutions, sulfuric acid uptake, proton conductivity at ambient temperature and the permeability of the Fe3+ ions through the membranes. The influences of the amount silica and the H2SO4 concentration on the swelling behavior were investigated. The composite membranes at SiO2 concentration in the range of 2.8-10 wt.% exhibited a proton conductivity of 1.65 × 10−2-1.68 × 10−2 Ohm−1 cm−1 in 4 N H2SO4. The negative effect of ferric ions on the proton conductivity of these membranes was established.