Pt-Ru nanoparticles supported on carbon nanotubes as methanol fuel cell catalysts

Bimetallic Pt-Ru alloy catalysts have been demonstrated to be more active than pure Pt catalysts in the electrooxidation of methanol. We report here a study on Pt-Ru nanoparticle catalysts supported on sonochernically functionalized carbon nanotubes. The catalysts were prepared by directly reducing the corresponding salts, K2PtCl4 and K2RUCl5, in an ethylene glycol aqueous solution containing dispersed carbon nanotubes. Three catalysts of different Pt to Ru atomic ratios, namely, Pt53Ru47, Pt69RU31, and Pt77RU23, were prepared for investigation of the compositional effects. It was shown that highly dispersed bimetallic Pt-Ru alloy nanoparticles with no agglomeration can be synthesized on the carbon nanotubes with average particle sizes of less than 3.0 nm in diameter. The Pt-Ru nanoparticles are uniform and cover only the outside of the carbon nanotubes. It was found that the polyol process produced alloy compositions that are not consistent with the metal ratios in the precursors. It was also found that the lattice spacings of these catalysts are different due to the different compositions of the catalysts. Cyclic voltammetry showed that the catalysts were electrocatalytically active in the electrooxidation of methanol. Among the three catalysts, the Pt53Ru47 catalyst produced the best performance. This catalyst was found to be the most stable, while the other two deactivated faster in the oxidation of methanol. All three Pt-Ru catalysts have higher electrocatalytic activities than a commercial catalyst Of Pt50RU50 supported on carbon black. However, the Pt69RU31 and Pt77RU23 catalysts showed poorer stability that can be justified by the bifunctional mechanism of bimetallic Pt-Ru alloys.