Hybrid Ion-Exchange Membranes Based on Heteroaromatic Sulfonic Acid Derivatives

Membranes exhibiting proton conductivity have been prepared by sol-gel synthesis using tetraethoxysilane 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 molecules 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 x 10(-2) or 0.55 x 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.