Progress Toward Accurate Through-Plane Ion Transport Resistance Measurement of Thin Solid Electrolytes

An instrument and procedure for evaluation of the through-plane ionic resistance and conductivity of polymer electrolyte membranes (PEMs) is presented. The approach facilitates rapid evaluation of bare, as-manufactured membranes over a wide range of temperatures and relative humidity conditions. The use of bare membrane is a key feature because a primary application is the characterization of the ionic conductivity of developmental materials for which testing a fuel cell is not practicable. Accurate evaluation of through-plane resistance and conductivity requires adjusting the measured high frequency resistance for nonmembrane ohmic contributions. Nonmembrane ohmic contributions, referred to in this work as the cell resistance, was determined by extrapolating to zero thickness a linear regression of the measured high frequency resistance vs membrane thickness. The cell resistance was a function of temperature and relative humidity. Using the through-plane resistance corrected for the cell resistance, the area specific resistance and conductivity of dispersion-cast Nafion NR-212 was observed to be the same in the through- and in-plane directions.