Substoichiometric titanium oxide (Ti4O7)-supported Pt catalysts were prepared and their electrochemical properties, particularly the effects of high-potential conditions on the activity and stability of Pt/Ti4O7 catalysts, were compared to those of Pt/C catalyst. Polarization measurements using membrane electrode assemblies revealed that the Pt/Ti4O7 cathode shows a similar activity for the oxygen reduction reaction as Pt/C catalyst at 80 degrees C. A high-potential holding test (1 h holding at 1.0-1.5 V vs anode) demonstrated that the Pt/Ti4O7 catalyst is quite stable against high potential up to 1.5 V. A single cell using a Pt/Ti4O7 cathode was operated at 80 degrees C, and voltage stability for > 350 h with H-2/O-2 was also demonstrated. (c) 2008 The Electrochemical Society.