Acetylene contamination in proton exchange membrane fuel cells (PEMFCs) significantly depends on cell operating conditions. In this work, acetylene contamination is studied by varying the acetylene concentration, cathode potential and temperature. Hysteresis in the cell performance response is observed during cycling tests with variations in acetylene concentration and cathode potential and is attributed to the potential dependency of acetylene redox reactions. The tolerance of PEMFCs to acetylene is established at approximately 23 ppm for a commercially available catalyst-coated membrane. For a cell poisoned by acetylene at a concentration above the tolerance value, performance losses are eliminated by bringing the ohmic compensated cell voltage into the acetylene oxidation (cell voltage increase) or hydrogenation (cell voltage decrease) regions. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.