The contamination effects of Fe3+ and Al3+ on the performance of polymer electrolyte membrane fuel cells were investigated by continuously injecting Fe3+ or Al3+ salt solution into the air stream of an operating fuel cell. Both metal ions individually caused significant cell performance degradation at a level of only 5 ppm mol in air. In addition, elevated temperature accelerated fuel cell performance degradation in the presence of Fe3+. Moreover, the presence of Fe3+ in an operating fuel cell resulted in the cell's sudden death, due to the formation of membrane pinholes that may have been promoted by the enhanced production of peroxy radicals catalyzed by Fe species. Half-cell tests in liquid electrolyte revealed that the presence of Al3+ in the electrolyte changed the kinetics and mechanisms of the oxygen reduction reaction by reducing the kinetic current densities and the electron transfer number. Crown Copyright (C) 2010 Published by Elsevier B.V. All rights reserved.