Estimation of Local Relative Humidity in Cathode Catalyst Layers of PEFC

A simple method is presented to estimate the local relative humidity (RH) in cathode catalyst layers (CCLs) of polymer electrolyte fuel cells (PEFCs). Based on impedance measurements under different experimental conditions, this technique provides a means to estimate the average value for RH using a correlation with the catalyst layer effective proton resistance. At zero current, a fully humidified anode raises the RH inside the CCL from a nominal 30% to almost 70%. A current density of up to also humidifies the cathode, while drying is observed between 0.4 and .