Proton-conductive inorganic–organic hybrid membranes synthesized from a trimethoxysilylmethylstyrene–fluorophenylvinyl acid copolymer

• Proton-conductive inorganic–organic hybrid membranes composed of Si–O networks and an aliphatic main-chain backbone.
• Wide range proton conductivity from low to fully hydrated conditions at 130 °C.
• The voltage–current curve for the membrane at 140 °C at 30% relative humidity.

Inorganic–organic hybrid membranes composed of Si–O networks and an aliphatic main-chain polymer backbone were synthesized from an alkoxysilane derivative and an F-substituted phenylvinylphosphonic acid via copolymerization and sol–gel reaction. Thus, (trimethoxysilylmethyl)styrene (TMSMS) was copolymerized with 3-fluorophenyl- vinylphosphonic acid (FC6H4VPA), and the product was hydrolyzed to afford an inorganic–organic hybrid composite. Spectroscopic analysis revealed that the inorganic–organic hybrid structure was constructed via the polymerization of TMSMS and FC6H4VPA and the condensation of methoxy-Si bonds. The membranes showed good thermal stability up to 180 °C, and it was found that the aliphatic chains bound to the F-substituted aromatic rings and the Si–O linkages in the hybrid membranes improved their mechanical properties. In addition, the proton conductivity of the membranes depended on the P/Si ratio of the product and increased as the P content increased. Notably, the conductivity at 130 °C for the hybrid membrane synthesized with a TMSMS/FC6H4VPA ratio of 1/6 was 1.6×10−3 S cm−1 and 6.4×10−2 S cm−1 at low and 100% relative humidity (RH), respectively, while its power density at 140 °C and 30% RH was 3.0 mW/cm2.

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