Synthesis and characterization of MoO x-Pt/C and TiO x-Pt/C nano-catalysts for oxygen reduction

Abstract

The oxygen reduction reaction (ORR) was studied at carbon supported MoO x -Pt/C and TiO x -Pt nanocatalysts 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 polycrystalline 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.