Protonic Transport inside Polymeric Membranes

Electrical conductivity σ of sulfonated polystyrene ion-permeable membranes has been measured from 80 to 160°C to determine the effects of glass transition temperature Tg on protonic transport. Membranes were loosely crosslinked (1%) and contained up to 10% by weight of styrene sulfonic acid. Membrane conductivity increases exponentially with rising temperature as given by σ=σ0exp−E/RT where σ0 is the preexponential factor and E is the apparent activation energy for the protonic conduction process. Activation energy values vary from 11.0 to 16.0 kcal/mole in the glassy state and 15.0 to 22.0 kcal/mole in the rubbery state. Self-diffusion coefficients of hydrogen ions within a typical sulfonated membrane above and below its Tg have been computed. The increase in protonic transport with rising temperature has been interpreted to be chiefly due to increasing concentration and mobility of hydrogen ions.