Progress Toward Accurate Through-Plane Membrane Resistance and Conductivity Measurement

An instrument and procedure for evaluation of the through-plane ionic resistance and conductivity of PEMs is presented. The approach facilitates rapid evaluation of bare membranes over a wide range of temperatures and relatively humidity conditions. Use of bare membrane is a key feature because a primary application is 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 non-membrane ohmic contributions. Non-membrane 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 (R) NRE-212 was observed to be the same in the through-plane and in-plane directions.