Electro-Oxidation of Methanol on Pt-Ru Nanoparticles
Li Ren and Yangchuan Xing. Department of Chemical & Biological Engineering, University of Missouri-Rolla, 1870 Miner Circle, Rolla, MO 65409
There has been a constant search for catalysts that are efficient in the electro-oxidation of methanol, a possible fuel in direct methanol fuel cells to power portable electronic devices. Electro-oxidation of methanol is a complex process involving transfer of six electrons and formation of numerous intermediates. The reactions are slow and require active catalytic sites for adsorption and oxidation of methanol as well as oxidation and desorption of adsorbed intermediates. The mostly studied catalyst for methanol electro-oxidation is Pt-Ru alloys. It has been found that Pt-Ru alloy catalysts generally have high catalytic activity. The reason has been attributed to the ability of Ru to form active oxygen species (-OH) at low electrode potentials that remove poisonous carbon monoxide on the Pt sites. Our research has focused on using carbon nanotubes (CNTs) as the support for Pt-Ru alloy catalysts. A variety of alloy catalysts were prepared on sonochemically functionalized CNTs. These catalysts have highly dispersed nanoparticles. The particles are generally less than 3 nm with a narrow size distribution. It has been found that CNTs with a definitive graphitic surface structure can enhance catalyst activity. Furthermore, we recently demonstrated that the Pt-Ru alloys showed a much improved activity when they are converted to hydroxides. This finding has led us to believe that Ru-OHx in the catalysts are the active sites to oxidize carbon monoxide adsorbed on the Pt sites. It was also demonstrated that the chemical states of the Pt-Ru alloys play a very important role in the catalyst activity. A comparison of different conditions further confirmed our conclusions. In this presentation, we will discuss these new findings.