The effect of pore diameter of gas diffusion layers (GDLs) in polymer electrolyte fuel cells (PEFCs) on cell performance was investigated at a standard operation temperature (65, 80 degrees C) and a subfreezing temperature (-5, -10 degrees C). Two types GDLs, one with a small pore diameter (2.4 mu m) and the other with a large pore diameter (4.3 pm), were examined. The cell with large pore diameter showed a higher limiting current than the cell with small pore diameter in the high current density region (over 0.5 A cm(-2)) at 65 degrees C (100% RH). This was because the larger pore diameter GDL has a more open gas diffusion network. On the other hand, the cell with small pores showed a favorable anti-flooding performance. It is considered that the smaller pores were able to form smaller water droplets, which were vaporized easily due to the contact area between the supplying air and the condensed water in the separator flow channel. The cell with small pores showed superior cold start-up performance in the ramped current mode at -5 degrees C. The cell temperature reached 0 degrees C more quickly due to the earlier switching to high current density than the cell with large pores, because the air was able to diffuse smoothly from inlet to outlet due to the smaller droplets of the cell with small pores. These experiments show that the pore diameter of GDLs affects the performance significantly, both during high humidity operation and during startup from subfreezing temperatures. (C) 2013 Elsevier Ltd. All rights reserved.