Catalysis of CO electrooxidation at Pt, Ru, and PtRu alloy. An in situ FTIR study

A comparative study of CO electrooxidation on different catalysts using in situ FTIR spectroscopy is presented. As electrode materials, polycrystallin e Pt and Ru and a PtRu (50:50) alloy are used. The latter is one of the wel l-known active alloys for CO oxidation. The potential dependence of the ban d frequencies for the CO stretch indicates the formation of relatively comp act islands at pure Pt and Ru, and a loose adlayer structure at the alloy. This loose structure has a positive effect on the rate of oxidative desorpt ion. CO submonolayer coverages are obtained by integrating the absorption b ands for CO2 produced upon oxidation of adsorbed CO. The band intensities m easured at Pt, Ru, and PtRu indicate an influence of the substrate on the a bsorption coefficient of the CO stretch. It is shown that for a correct des cription of the catalyst properties toward CO electrooxidation, it must be distinguished between bulk and adsorbed CO. In contrast to the statement of most of the recent papers that a PtRu alloy (50:50) is the material with t he highest activity for CO oxidation, it is demonstrated and rationalized i n the present paper that for bulk CO oxidation pure Ru is the best catalyst .