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Membranes exhibiting proton conductivity have been prepared by sol-gel synthesis using tetra ethoxysilane and heteroaromatic sulfonic acid derivatives (2 phenyl 5 benzimidazolesulfonic acid and 3 pyridinesulphonic acid) in the presence of phosphoric acid and polyvinyl butyral. The membranes are gels composed of a polyvinyl butyral polymer matrix with uniformly distributed particles of silica containing mol ecules of heteroaromatic sulfonic acid derivatives mechanically incorporated in its network structure. The membranes synthesized from 2 phenyl 5 benzimidazolesulfonic acid or 3 pyridinesulphonic acid exhibit a conductivity of 0.1 × 10 -2 or 0.55 × 10 -2 S/cm at 353 K, an ion exchange capacity of 2.70 or 1.84 mequiv/g, and a proton transfer activation energy of 24.93 or 21.73 kJ/mol, respectively; at a relative water content of 50%, the tensile strength is 4 or 6 MPa and the elastic modulus is 128 or 191 MPa, respectively.

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