The influences of the heat-treatment of Ketjen Black EC300J in the temperature range 1000-2000 degrees C on the catalytic activity of loaded Pt for oxygen reduction reaction (ORR) were studied. A maximum enhancement in the specific ORR activities (SOA) was observed for the carbon heat-treatment at 1500 degrees C. The heat-treatment of carbon induced decreases in porosity and the development of graphitic structures; however, no direct correlations were observed between these properties and the SOA. Transmission electron microscopy and X-ray photoelectron spectroscopy, respectively, showed enhancements in the uniformity of the Pt particle size distribution and of the extent of surface reduction of Pt with increasing heat-treatment temperature (HTT). Cyclic voltammetry in 0.5 M H2SO4 aqueous solution detected changes in the hydrogen adsorption at 0.12 V vs. a reversible hydrogen electrode, depending on the HTT of the carbon support, and this was ascribed to hydrogen adsorption on the Pt(110) surface, the most active crystal face of Pt for ORR. The fraction of Pt atoms belonging to the (110) surface out of the total surface Pt atoms showed an excellent correlation with the SOA. Heat-treatment of the carbon support was therefore concluded to be an effective treatment for enhancing the SOA of Pt. (C) 2012 Elsevier B.V. All rights reserved.