Effect of pressure on through-plane proton conductivity of polymer electrolyte membranes

This study reports an electrochemical analogy with the invention of a 2-electrode impedance cell oriented to analyze through-plane ionic conductivity of polymer electrolyte membranes. The membranes are utilized under varied pressures in assembled membrane stacks for water treatment, energy conversion, and storage devices. In addition, polymeric membranes are a viscoelastic material, which allow their shape to change according to the external pressure. Therefore, the impedance under controlled pressure is crucial information for analyzing their electrochemical properties. In this regards, an apparatus is designed to indicate the absolute pressure in the sample and the resulting thickness of the sample while measuring the impedance. As a model analysis, we employ a proton conducting membrane, Nafion®117, Nafion®115, and Nafion®112. The membrane thickness in a wet state was found to be significantly variable with the pressure, and the impedance spectra showed a clear dependence on the pressure. Therefore, this new approach facilitates a precise impedance analysis, since the exact sample thickness is indicated, along with the absolute pressure in the sample. As such, this technique could be a useful tool for analyzing the through-plane conductivity of polymer electrolyte membranes with high accuracy.