Synthesis of organosiloxane-based inorganic/organic hybrid membranes with chemically bound phosphonic acid for proton-conductors

Proton conductive inorganic–organic hybrid membranes were synthesized from 3-glycidoxypropyltrimethoxysilane (GPTMS) and phosphonoacetic acid (PA) with various ratios by a sol–gel process. Self-standing, homogeneous, highly transparent membranes were synthesized. TG–DTA analyses indicated that these membranes were thermally stable up to 200 °C. The results of FT-IR and 13C NMR revealed that phosphonic acid groups of PA were chemically bound to organosiloxane network as a result of reaction between PA and GPTMS. The leach out of phosphonic acid groups from GPTMS–PA to water was reduced compared with phosphoric acid groups from GPTMS–H3PO4. The proton conductivity of the hybrid membranes increased with phosphonic acid content. The conductivity of GPTMS/PA with a 1/1.05 ratio at 130 °C was 8.7 × 10−2 S cm−1 at 100% relative humidity (RH).