In this research the performance of proton exchange membrane fuel cells (PEMFC's) was studied, using pore-filling electrolyte membranes based on plasma-activated microporous polyethylene (PE) matrices coated with sulfonated hydrogenated butadiene-styrene block copolymer (SHSBS). The voltage-current and power density curves were recorded under different experimental temperature and pressure conditions. In addition, an electrochemical study was completed by means of electrochemical impedance spectroscopy (EIS) in the symmetrical mode, adjusting the electrical response obtained to an equivalent circuit. which allows for isolation of the different processes occurring within the system. Two parameters were taken into account in the study: the membrane's proton transport or ion resistance (R-1) and its charge transfer resistance (R-2). The results obtained indicate that SHSBS shows a single cell behaviour which is comparable to that of the commercial membrane Nafion (R). In contrast, the performance of the PE-SHSBS pore-filling electrolyte membranes was lower than that of Nafion (R). Likewise it was found that the different plasma treatments applied to the microporous PE matrix have an effect on the proton exchange capacity of the pore-filling electrolyte membrane. EIS allowed to determine the ion resistance of the proton exchange membrane, and it was demonstrated that the kinetics of the cathodic reaction and the cathode itself are decisive elements in membrane performance and hence prime objectives to be optimized, when the reduction of the overvoltages is at stake, which are currently observed in the polarization curve at low and high power densities. (C) 2009 Elsevier B.V. All rights reserved.