Identification of Ru phases in PtRu based electrocatalysts and relevance in the methanol electrooxidation reaction

A relationship between the chemical state of Ru on bimetallic PtRu bulk samples and their performance in both CO and methanol electrooxidation has been established. The nature of the Ru species in the bimetallic samples has been scrutinized by means of XPS, XRD and TPR. The following Ru species were detected; reduced ruthenium (Ru0), anhydrous RuO2 and hydrous Ru oxide. The actual nature of the latter species consists of two amorphous oxides of general formula RuO2·xH2O and RuOx(OH)y as determined from the XPS analysis. Irrespective of the Ru phases, all PtRu catalyst studied display a similar CO oxidation pattern. However, methanol electrooxidation was found dependent on the Ru phases. Thus, catalysts containing Ru0 are more active in the methanol oxidation reaction, at least during the early stages of the reaction. More stable catalyst are obtained if amorphous Ru oxide phases are the predominant ones.