Ùaeªaeç_AEÄae¡ÜfÛìT^Pt¯éŲ»VŶfS Pt G}m¨ß媻ae¸ô³ãïColloidal Pt nanoparticles, which contained 23÷ tetrahedral particles, 8÷ cubic particles, 49÷ other poly hedral particles, and 20÷ unidentied particles, were prepared through the reduction of Pt cations by dis solved H 2 in the presence of sodium polyacrylate (SPA). The Pt particles were supported on carbon black and heated at 260 C in N 2 ow. The prepared catalyst (Pt/CSPA) contained 18÷ tetrahedral particles, 5÷ cubic particles, 29÷ other polyhedral particles, and 48÷ unidentied particles. Although the mean Pt parti cle size of Pt/CSPA estimated by transmission electron microscopy (TEM) (9.1 nm) was larger than that of a conventional electrocatalyst (Pt/Cref) (2.4 nm) for oxygen reduction reaction (ORR), the specic activi ties of Pt/CSPA for ORR based on the particle size measured from the TEM image and on its electrochemi cal surface area were 1.8 and 1.6 times as high as those of Pt/Cref, respectively.