Estimation of Local Relative Humidity in Cathode Catalyst Layers of PEMFC

A method is presented to estimate the local relative humidity in cathode catalyst layers of PEM fuel cells. Based on impedance measurements under different experimental conditions, this technique allows the estimation of an average value for relative humidity using a correlation with the catalyst layer effective proton resistance. A fully humidified anode was found to increase the relative humidity of the nominally drier cathode because of water permeation through the membrane, to as much as almost 70% for a nominal 30% when the anode RH was held at 100%.