Journal of Power Sources 185 (2008) 871–875 Contents lists available at ScienceDirect Journal of Power Sources journal homepage: www.elsevier.com/locate/jpowsour Short communication Synthesis and characterization of nanostructured PtCo-CeO x /C for oxygen reduction reaction Kang Hee Lee, Kyungjung Kwon ∗ , Victor Roev, Duck Young Yoo, Hyuk Chang, Doyoung Seung Energy & Environment Lab, Samsung Advanced Institute of Technology, Nongseo-dong, Giheung-gu, Yongin-si, Gyeonggi-do 446-712, Republic of Korea article info Article history: Received 16 May 2008 Received in revised form 28 July 2008 Accepted 2 September 2008 Available online 19 September 2008 Keywords: Electrocatalyst Polymer electrolyte membrane fuel cell Oxygen reduction Platinum Cerium Platinum–cobalt alloy abstract Highly dispersed PtCo–CeO x couples of fine Pt 3 Co alloy particles with adjacent CeO x are synthesized on a carbon support using the modified colloid method. The average sizes of Pt 3 Co and CeO x particles are approximately 1.7 and 4nm, respectively. According to XPS studies, the CeO x particle consists of a CeO 2 phase crystal for the core and a Ce 2 O 3 phase for the shell. The CeO x -containing electrocatalysts of PtCo–CeO x and Pt–CeO x show improved electrochemical performances for the oxygen reduction reaction compared with PtCo and Pt electrocatalysts without CeO x in both ring-disc electrode and cell tests. It seems that the unsaturated Ce 2 O 3 phase of the CeO x surface causes the facile adsorption and desorption of oxygen, leading to an enhanced oxygen supply to the PtCo alloy. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Polymer electrolyte membrane fuel cells (PEMFCs) have attracted much interest because of their extended application in various fields such as mobile power sources and residential power systems [1]. One of the major obstacles that should be overcome for the commercialization of PEMFCs is to find a more efficient cat- alyst than Pt for the oxygen reduction reaction (ORR), which is the cathodic reaction of a PEMFC. Platinum alloyed with Co, Fe, Ni, Cr or V has received much sci- entific attention as the cathode catalyst because of its superior ORR activity to pure Pt [2–6]. The improvement in the ORR has been ascribed to modifications of the geometric and electronic struc- tures, as well as the Pt–Pt bond distance and d-electron vacancy, by alloying with the transition metals [7]. In fact the modifications could affect the bond strength between Pt alloy and surface oxygen. The kinetics of the ORR is determined by the number of free Pt sites available for the adsorption of oxygen. The fractional coverage by OH occupied on Pt alloys is related to their d-band centre position. In a recent study on this electronic effect [8], PtCo alloy having an ∗ Corresponding author. Tel.: +82 31 280 8162; fax: +82 31 280 9359. E-mail address: k.kwon@samsung.com (K. Kwon). appropriate energy level of the metal d-band shows a better ORR activity, which is attributed to its lower OH coverage in the ORR. The supply rate of oxygen is another significant factor that could affect the kinetics of the ORR. The high overpotential in the cath- ode of hydrogen-based PEMFCs could be overcome through rapid oxygen transfer to the Pt catalyst. Additions of Sn, Mo and W to the oxide phase in fuel cell electrodes have been studied to facilitate the supply of oxygen species leading to improved cell performance [9,10]. CeO 2 , a widely used rare earth metal oxide catalyst, is effi- cient for the control of automotive emissions because of its ability of oxygen storage [11]. CeO 2 has also been used as an electrolyte material because of the high oxygen transfer ability derived from its own oxygen defects [12]. It has been reported [13–18] that CeO 2 promotes CO oxidation in the anode of direct alcohol fuel cells by supplying oxygen ions to the Pt catalyst. Although the oxygen sup- ply problem more critically affects the fuel cell performance on cathode compared with anode, the application of CeO 2 for the ORR is described only in a few studies [19,20]. As a promising design for cerium-containing electrocatalyst for the ORR, we tried to com- bine optimally designed cerium oxide with a PtCo alloy, which is one of the most effective ORR catalysts [21]. In this study, PtCo alloy–CeO x is prepared by a modified colloid method. Although this method has already been adopted [22] to prepare PtRu alloy for a direct methanol fuel cell (DMFC) anode catalyst, the fabrica- 0378-7753/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jpowsour.2008.09.029