We present Pt particle size and fuel cell results for carbon black, carbon fibers, and single-walled carbon nanotubes (SWCNTs). The Study investigated how high-temperature liquid and supercritical fluid synthesis conditions could influence the Pt particle size and fuel cell performance of these nanocomposite catalyst materials. High-temperature methanol is a suitable medium for Pt particle size deposition. generating smaller particles (90% measuring <= 5 tim). The addition of a surfactant, Such as sodium dodecyl sulfate, to the fluid medium improved the fuel cell performance and Pt utilization of all 3 supports by 27 to 63%, with the best catalyst material, Pt/SWCNTs. having a peak power density of 449 mW/cm(2). This synthesis technique was a very fast (< 5 min) process with no reactor sidewall effects on Pt particle size or yield. (c) 2008 Elsevier Inc. All rights reserved.