Determination of Ionic and Electronic Resistivities in Carbon/Polyelectrolyte Fuel-Cell Composite Electrodes

Rational design of electrode materials for polymer electrolyte fuel cells requires a knowledge of how changes in material composition affect basic physical characteristics such as charge-transport properties. We present a simple method by which the electronic resistance of a thin layer of carbon/Pt/Nafion fuel-cell electrode composite material may he measured by de polarization and then combined with ac impedance measurements to compute the ionic resistance of the layer. Further support of this technique is derived from an ac impedance test designed to simultaneously express both the measured electronic and the computed ionic resistance. We also demonstrate the use of the technique in a composition-dependence study, namely, examination of the effect of glycerol on the ionic and electronic resistances in a thin catalyst layer.