Physical impedance model consisting of 5 equivalent circuit elements to fit the impedance data measured with the PEM single-cell at OCV: Ru – uncompensated (electrolyte) resistance, Cdl – electrical double layer capacitance, Rct – the charge transfer resistance due to the oxygen reduction reaction at the cathode side, Rads and Cads are the adsorption resistance and capacitance, respectively, describing the impedance response due to possible specific quasi-reversible adsorption of the sulfonate-groups of Nafion at the Pt-electrocatalyst surface [12].