Fundamental aspects in electrocatalysis: from the reactivity of single-crystals to fuel cell electrocatalysts

Abstract

A chemical modification by electrochemical deposition of Ru is performed on Pt(111) yielding mostly monoatomic Ru islands. From the investigation by scanning tunneling microscopy (STM) and by infrared spectroscopy of adsorbed CO it is found that nanostructured Pt–Ru electrodes exhibit distinct characteristics regarding CO oxidation which are due to a cooperative reaction mechanism involving CO surface mobility. The CO mobility can also be directly detected by IR spectroscopy on Pt(111) surfaces that have been modified by Ru deposition only in the center of the crystal. The presence of a second peak in the cyclic voltammogram (CV) for CO monolayer oxidation is most likely due to a dependence of the diffusion rate on the coverage of CO. Carbon supported Pt–Ru catalysts are prepared by the sulfito method and investigated regarding methanol oxidation. Although the structural characterization of the catalysts shows no evidence for alloy formation, a high mass activity is observed which is comparable to commercial catalysts. The catalyst weight loading has been varied systematically to investigate the influence of this parameter on the performance of the catalyst. For a temperature of 25 °C the mass activity increases with increasing catalyst mass loading up to about 55 wt.%. Then a plateau in the mass activity versus weight loading is reached. For 65 °C, however, a maximum mass activity is observed at 60 wt.%. These results show a different pattern of performance relative to loading with changing temperature indicating that some tailoring of the catalyst to different operating conditions could be beneficial.