Platinum nanocatalysts supported on surface-oxidized single-walled carbon nanotubes (Pt/o-SWNT) were prepared by the aqueous solution reduction of H2PtCl6 with HCHO. The nanocatalysts contain 10 wt% Pt (by EDS) on o-SWNTs. TEM images show that the Pt particle size is in the range of 5-10 nm. X-ray diffraction (XRD) analysis indicates the presence of platinum in the fee phase and the average size of the particles calculated from the XRD peak widths agreed well with TEM results. For comparison of electrochemical performance, platinum nanocatalysts supported on purified SWNTs (Pt/p-SWNT) and on Vulcan XC-72 (Pt/C) were also prepared by the HCHO reduction method. The cyclic voltammetry results indicate that Pt/o-SWNT catalyst displays a higher performance than Pt/p-SWNT and Pt/Vulcan XC-72. The difference may be due to the disentanglement of the SWNT ropes when treated with nitric acid and the oxidation of SWNTs caused more surface functional groups resulting in a higher density of Pt particles. (c) 2004 Elsevier B.V. All rights reserved.