Electrochimica Acta 54 (2009) 2404–2409 Contents lists available at ScienceDirect Electrochimica Acta journal homepage: www.elsevier.com/locate/electacta Synthesis and characterization of MoO x -Pt/C and TiO x -Pt/C nano-catalysts for oxygen reduction N.R. Elezovic a,∗ , B.M. Babic b , V.R. Radmilovic c , Lj.M. Vracar d , N.V. Krstajic d a Institute for Multidisciplinary Research, Kneza Viseslava, 1a, Belgrade, Serbia b Vinˇ ca Institute of Nuclear Sciences, Belgrade, Serbia c National Center for Electron Microscopy, LBLN University of California, Berkeley, USA d Faculty of Technology and Metallurgy, University of Belgrade, Belgrade, Serbia article info Article history: Received 21 November 2007 Received in revised form 27 February 2008 Accepted 5 March 2008 Available online 15 March 2008 Keywords: Oxygen reduction reaction MoOx-Pt/C catalyst TiOx-Pt/C catalyst Nanoparticles Acid solution abstract The oxygen reduction reaction (ORR) was studied at carbon supported MoO x -Pt/C and TiO x -Pt nanocat- alysts in 0.5 mol dm -3 HClO 4 solution, at 25 ◦ C. The MoO x -Pt/C and TiO x -Pt/C catalysts were prepared by the polyole method combined by MoO x or TiO x post-deposition. Home made catalysts were characterized by TEM and EDX techniques. It was found that catalyst nanoparticles were homogenously distributed over the carbon support with a mean particle size about 2.5 nm. Quite similar distribution and particle size was previously obtained for Pt/C catalyst. Results confirmed that MoO x and TiO x post-deposition did not lead to a significant growth of the Pt nanoparticles. The ORR kinetics was investigated by cyclic voltammetry and linear sweep voltammetry at the rotating disc electrode. These results showed the existence of two E - log j regions, usually observed with poly- crystalline Pt in acid solution. It was proposed that the main path in the ORR mechanism on MoO x -Pt/C and TiO x -Pt/C catalysts was the direct four-electron process with the transfer of the first electron as the rate-determining step. The increase in catalytic activity for ORR on MoO x -Pt/C and TiO x -Pt/C catalysts, in comparison with Pt/C catalyst, was explained by synergetic effects due to the formation of the interface between the platinum and oxide materials and by spillover due to the surface diffusion of oxygen reaction intermediates. © 2008 Elsevier Ltd. All rights reserved. 1. Introduction One of the main goals of current research is low temperature methanol fuel cell system as a promising method of energy pro- duction [1,2], but the system with a lot of problems that need to be solved. Anodic reaction in the cell is oxidation of methanol a reaction whose poor kinetics is still problem, although methanol is inexpensive liquid fluid, easy to transport and store [3,4]. Oxygen reduction as cathodic reaction in the cell exhibits slow and compli- cated kinetic behaviour that is also a problem in term of efficiency of the cell [5,6]. One of the route dealing with a slow oxygen reduc- tion is the development of a good catalyst that will have, at the same time, high methanol tolerance in the case of possible cross- over of methanol from the anode to the cathode through the proton exchange membranes. To avoid the last problem the relevant proton exchange membranes [7,8] should be developed, too. The oxygen reduction on the platinum is a structure sensitive reaction and the activity of the surface generally increases as the ∗ Corresponding author. Tel.: +381 11 3303688; fax: +381 11 3055289. E-mail address: nelezovic@tmf.bg.ac.yu (N.R. Elezovic). surface area decreases as a reason of the variation of the different Pt crystal planes exposed to the electrolyte as a function of the particle size [9]. The decrease of Pt particle size reduces the energy of adsorbed oxygen species that facilitates the reduction of these species leaving more Pt sites available for the oxygen reduction. One of the ways in making a good catalyst for ORR, proposed in the literature [10], was Pt deposition on suitable metal nanopar- ticles. These new class of catalysts consisted of Pt and another transition metal (Ir, Ru, Rh, Pd, Au, Re or Os) deposited on a car- bon supported Pt nanoparticles had a very high activity compared to that of pure Pt, and a considerably lower Pt content. The authors suggested that the destabilization of OH on Pt due to the adsorbed OH or O on metal is responsible for enhancing the ORR kinetics. The supporting material for the functioning of the catalysts is very important and it should be a good combination of excellent electronic conductivity and a good corrosion resistivity. Carbon or graphite is the most widely used catalyst support as it has very high surface area and very good electronic conductivity [11]. More recently we synthesized Pt catalyst using Ebonex as a sup- port and found the enhancement of the catalytic activity towards oxygen reduction. This was very evident through the change of elec- trochemically active surface area and ten times enhancement of 0013-4686/$ – see front matter © 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.electacta.2008.03.015