Distributed effects of cation contamination on polymer electrolyte fuel cells (PEFC) were investigated at a fixed concentration of 5 ppm of Ca2+ in the air stream of an operating fuel cell. A special purpose MEA was prepared using five layers of membrane, and four Pt wires (electrodes) were inserted between the membrane layers. These Pt electrodes were used to monitor the through plane potential due to the permeation of hydrogen and oxygen from the anode and the cathode, respectively as well as the resistance distribution across the membrane thickness. At the beginning of the test, oxygen permeated from the cathode to the first layer of the membrane. After 32 h, oxygen continued to permeate from cathode to the other layers of the membrane. The cell performance deteriorated, when CaSO4 solution was injected as a contaminant. Within 21 h of contaminant injection, the cell voltage dropped to less than 200 mV. High frequency resistance (HFR) increased more than 50% in the individual membrane layer that was located close to the cathode. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.