In Situ, Through-Plane Measurements of Ionic Potential in a PEMFC Catalyst Layer

A novel apparatus for measuring in situ, through-plane, ionic potential distribution within the cathode catalyst layer of a polymer electrolyte membrane (PEM) fuel cell is presented here. This new diagnostic method makes use of a micro-structured electrode scaffold (MES), which is a stack of alternating insulating and sensing layers that surround a 100 µm diameter cylinder of catalyst layer material. Here we present measurements of ionic potential at four points through the thickness of a PEM fuel cell cathode. These preliminary results show significant variations of the ionic potential within the electrode at high currents. In addition, the local ionic potential provides an accurate measure of the local IR-free potential in the catalyst layer. Possible applications of the ionic potential data gathered from the MES include investigating mass and charge transport limitations, spatially characterizing electrode kinetics, and validating porous electrode models.