Three high-purity TiO2 (anatase) powders (T-PF6, T-BF4, and T-conventional) were prepared by the sol-gel method with/without ionic liquid as template and calcinations at 450 degrees C. These powders were, then, characterized to investigate their differences in morphological properties. Electrochemical performances of the H-2/O-2 PEMFCs employing the Nafion composite membranes with these three TiO2 powders as fillers were studied over 80-120 degrees C under 50% and 95% relative humidity (RH). The result showed that the order of the fillers effect on the performance at 80 and 90 degrees C was the same as that of the TiO2 filler's specific surface area (i.e. T-PF6 > T-conventional > T-BF4 > P25, a commercially available nonporous TiO2 powder). However, the order between T-conventioal and T-BF4 was reversed at 110 and 120 degrees C under 50% RH. This indicates that the size and the amount of mesopores, which better confined the water molecules, were significant contributing factors to the performances at the higher temperatures. The best power density obtained under 50% RH at 120 degrees C and a voltage of 0.4V was from the PEMFC with the T-PF6-containing Nation composite membrane. It was about 5.7 times higher than the value obtained from that with the recast Nation membrane. (C) 2007 Elsevier B.V. All rights reserved.