Sonochemistry was applied to prepare Pt-Ni electrocatalyst materials. To promote uniform alloying, a route based on sonication of precursor metal salts in non-aqueous solution containing a strong reducing agent was used as an alternative to sonication in aqueous solution. Metal nanoparticles consistent with the Pt3Ni stoichiometry were formed by sonication of a reaction mixture that contained a 3:1 mole ratio of Pt4+ and Ni2+ ions in tetrahydrofuran (THF). After isolation, the metal nanoparticles were characterized with the use of transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), X-ray diffraction and voltammetry methods. The structural and electrochemical studies indicate the sample consisted mainly of particles in the 2 nm-5 nm size range with characteristics of a uniform Pt3Ni alloy. Following activation by potential cycling (20 cycles between 0.05 V and 1.2 V versus a reversible hydrogen electrode at 100 mV/s) to form a Pt-rich surface layer, the sonochemically prepared Pt-Ni nanoparticles showed a three-fold enhancement in O-2 reduction kinetics compared with a commercial Pt catalyst. (C) 2011 The Electrochemical Society. [DOI: 10.1149/2.029203jes] All rights reserved.