ABSTRACT
ABSTRACT: Ultrahigh vacuum spectroscopies combined with electrochemistry have been used for the last two decades as a powerful tools for determining the details of surface structure of a variety of electrode materials of interest to heterogeneous electrocatalysis. In this chapter, recent results obtained by these techniques by this group in studies of well-defined platinum/ruthenium electrodes as catalysts for methanol electrooxidation processes are summarized. Some related work by other investigators is also reviewed. Highlighted are principles involved in the oxidation reactions, such as confirmation by the use of Auger electron spectroscopy of the spontaneous deposition process of ruthenium, first indicated by voltammetry: evidence that such spontaneously produced deposit enhances catalytic activity of platinum toward methanol oxidation in electrolytic media; elucidation of coverage-charge relationships for ruthenium electrodeposition; and demonstration of platinum-substrate surface structure effects on Tafel slopes involved in methanol oxidation and on reaction turnovers (reactivity). We have found that the Pt(111)/Ru electrode is the best laboratoryscale fuel cell anode for methanol oxidation and concurrently identified the Pt(111)/Ru as the most active surface phase in fuel cell industrial catalysts. Based on these results, we strongly believe that the structural optimization of catalytic Pt/Ru materials is needed to increase the representation of the (111) phase at the expense of other surface phases. We also conclude that crystallographic variables should be exploited in syntheses of novel metal-alloy catalysts for fuel cell use. The structural component may add to the improvement in the efficiency of anode catalysis needed to make direct oxidation methanol fuel cell a viable alternative to other power sources considered for various energy and transportation use.
