The cold-start behavior and the effect of sub-zero temperatures on fuel cell performance were studied using a 25-cm(2) proton exchange membrane fuel cell (PEMFC). The fuel cell system was housed in an environmental chamber that allowed the system to be subjected to temperatures ranging from sub-freezing to those encountered during normal operation. Fuel cell cold-start was investigated under a wide range of operating conditions. The cold-start measurements showed that the cell was capable of starting operation at -5 degrees C without irreversible performance loss when the cell was initially dry. The fuel cell was also able to operate at low environmental temperatures, down to -15 degrees C. However, irreversible performance losses were found if the cell cathode temperature fell below -5 degrees C during operation. Freezing of the water generated by fuel cell operation damaged fuel cell internal components. Several low temperature failure cases were investigated in PEM fuel cells that underwent sub-zero start and operation from -20 degrees C. Cell components were removed from the fuel cells and analyzed with scanning electron microscopy (SEM). Significant damage to the membrane electrode assembly (MEA) and backing layer was observed in these components after operation below -5 degrees C. Catalyst layer delamination from both the membrane and the gas diffusion layer (GDL) was observed, as were cracks in the membrane, leading to hydrogen crossover. The membrane surface became rough and cracked and pinhole formation was observed in the membrane after operation at sub-zero temperatures. Some minor damage was observed to the backing layer coating Teflon and binder structure due to ice formation during operation. (c) 2006 Elsevier B.V. All rights reserved.