Pt on ceria (CeOx) particles supported on carbon black (CB) were synthesized using the combined process of hot precipitation and impregnation methods. During 30 cycles of cyclic voltammetry pre-treatment in the potential ranging from -0.2 to 1.3 V (V vs. Ag/AgCl), it was observed that a small amount of CeOx, which consisted of the interface region between Pt and CeOx, remained on Pt particles. Other free CeOx particles were dissolved into H2SO4 aqueous solution. To develop the Pt-CeOx/CB catalyst, the surface chemical states, the net chemical composition, morphology and electrochemical behavior in H2SO4 aqueous solution were characterized. Our microanalysis and electrochemical analysis indicate that the active CeO2 with high specific surface area provides the continuous amorphous cerium oxide (Ce3+, Ce4+) layer with pores on the surface of Pt particles. It is concluded that the amorphous cerium oxide layer on Pt inhibits the oxidation of Pt surface and contributes to enhancement of the activity on Pt cathode. The single cell performance was also improved using the Pt-CeOx/CB cathode. Based on all data, it is expected that the design based on characterization of the interface between Pt and small amount of amorphous cerium oxide layer could help in preparation of more active Pt catalyst. (C) 2011 Elsevier Ltd. All rights reserved.