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

摘要

The oxygen reduction reaction (ORR) was studied at carbon supported MoO{sub}x-Pt/C and TiO{sub}x-Pt nanocat-alysts in 0.5 moldm{sup}(-3) HClO{sub}4 solution, at 25℃. The MoO{sub}x-Pt/C and TiO{sub}x-Pt/C catalysts were prepared by the polyole method combined by MoO{sub}x or TiO{sub}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{sub}x and TiO{sub}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 - logj regions, usually observed with poly-crystalline Pt in acid solution. It was proposed that the main path in the ORR mechanism on MoO{sub}x-Pt/C and TiO{sub}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{sub}x-Pt/C and TiO{sub}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.