Synthesis of poly(3-(4-ethoxysulfonylphenoxy)-2-methylpropyl)silsesquioxane and its application as a proton-conducting membrane

Abstract

A polysilsesquioxane-based organic-inorganic hybrid membrane was prepared and applied as a proton-conducting membrane for fuel cells. poly(STES-ran-MTES), a random copolymer of ethyl 4-(2-methyl-3-triethoxysilylpropoxy)benzenesulfonate (STES) and triethoxy(methyl)silane (MTES) was synthesized by hydrolysis and condensation in the presence of hydrochloric acid under a nitrogen stream. The molecular weight was 7500–7600 g mol−1, and the percentage of hydrolyzed ethoxysulfonyl group was 32–50%. A poly(STES-ran-MTES) membrane was prepared by heating for several days, which showed thermal resistivity up to 200 °C and proton conductivity of 2.0 × 10−5 to 1.1 × 10−3 S cm−1 at room temperature. By contrast, a membrane of a block copolymer, poly(SPES-block-PMS), showed proton conductivity of 2.5 × 10−3 S cm−1. The proton conductivity of the poly(3-(4-ethoxysulfonylphenoxy)-2-methylpropyl)silsesquioxane (SPES) membrane increased from 2.7 × 10−3 S cm−1 at 25 °C to 1.0x10−2 S cm−1 at 110 °C. The proton conductivity of the SPES membrane increased from 2.7 × 10−3 S cm−1 at relative humidity (RH)=25–30% to 2.0 × 10−3 S cm−1 at RH=60% and 1.4 × 10−1 S cm−1 at RH=90%. The mixture of SPES and poly(vinyl alcohol), poly(ethylene oxide) or polyoctahedralpolysilsesquioxane showed proton conductivities of 2.7 × 10−3, 1.5 × 10−3 and 2.5 × 10−3 S cm−1, respectively, at 25 °C and RH=25–30%. The open-circuit voltage of the SPES membrane was 0.92 V. A polysilsesquioxane-based organic-inorganic hybrid membrane was prepared and applied as a proton-conducting membrane for fuel cells. A membrane of a random copolymer of ethyl 4-(2-methyl-3-triethoxysilylpropoxy)benzenesulfonate and triethoxy(methyl)silane showed proton conductivity of 2.0 × 10−5 to 1.1 × 10−3 S cm−1 at room temperature. A membrane of a block copolymer of poly(3-(4-ethoxysulfonylphenoxy)-2-methylpropyl)silsesquioxane (SPES) and polymethylsilsesquioxane showed proton conductivity of 2.5 × 10−3 S cm−1. The mixture of SPES and poly(vinyl alcohol), poly(ethylene oxide), or polyoctahedralpolysilsesquioxane showed proton conductivity of 2.7 × 10−3, 1.5x10−3 or 2.5 × 10−3 S cm−1, respectively. The open-circuit voltage of the SPES membrane was 0.92 V.