THE EFFECT OF TEMPERATURE ON THE EQUILIBRIUM AND TRANSPORT-PROPERTIES OF SATURATED POLY(PERFLUOROSULFONIC ACID) MEMBRANES

The equilibrium and transport properties of a poly(perfluorosulfonic acid) membrane containing a dilute sulfuric acid solution are investigated over the temperature range from 20 to 90-degrees-C, which is of interest for polymer-electrolyte fuel cells. The membrane porosity, proton diffusion coefficient, and electrokinetic permeability are measured and tabulated as a function of temperature. A combination of electrochemical and radiotracer techniques are employed. The electrokinetic Peclet number, a dimensionless group that characterizes the importance of electro-osmotic water transport by the membrane, is shown to have only a slight dependence on temperature. A previously developed equilibrium model, containing no adjustable parameters, is used to describe the equilibrium data. Published values for the dipole moment, dielectric constant, and index of refraction of water, along with the ionic radii of protons and bisulfate ions are the only model inputs that are not measured directly. The equilibrium model also is shown to be in qualitative agreement with published Monte Carlo simulations of counterion profiles near a charged surface, such as a membrane pore wall.