Distributed performance of a polymer electrolyte fuel cell (PEFC) is studied both in galvanostatic and potentiostatic mode during in-situ injection of Ca2+ in the air stream using a segmented cell. In the galvanostatic mode, segments near the inlet are affected first by the contaminant resulting in decreased current density. At the same time, despite the presence of contaminants, current density for the other segments increases in order to maintain constant total current. In the potentiostatic mode, all segments are affected by the contaminants simultaneously and the current density in all segments decreases with time. The performance of the downstream segments is lower than the upstream segments. During both tests, the contaminant is found to precipitate on both the cathode flow field and the cathode GDL surface. As the test progresses, the contaminant penetrates into the GDL and deposits, causing mass transport losses. (C) 2015 Elsevier B.V. All rights reserved.