Research toward designing high activity catalysts for fuel cells: structure and reactivity

We address some basic issues involved in catalytic activity for anode appli cations in the direct oxidation methanol fuel cell. We first report methano l oxidation data obtained with a Johnson-Matthey nanoparticle catalyst used both "as received" or processed by electrochemical reduction. Full chronoa mperometric curves for the oxidation process that develop over a period of ca. 18 hours (until the current stabilizes) are presented. The steady-state currents depend on the extent of the catalyst electroreduction, are smalle r than those previously obtained from the Pt(111)/Ru catalyst, but are sign ificantly higher than from the Pt(100)/Ru surfaces. Next, polycrystalline p latinum was used as a substrate onto which controlled amounts of ruthenium and osmium were deposited, and such prepared surfaces were used as the cata lyst for methanol oxidation. Current densities obtained from all surfaces a re critically compared. Apparently, osmium added to platinum is an enhancin g element for the methanol oxidation process but at low potentials, advanta geous for fuel cell use, osmium is less effective than ruthenium. The enhan cing strength of osmium increases as the electrode potential increases and, at 0.6 V, nearly equals that of Pt/Ru. The significance of this observatio n with respect to the activity of the ternary Pt/Ru/Os catalyst for methano l oxidation is highlighted in the paper Conclusions. We also present prelim inary STM data obtained on Pt single crystal surfaces deposited with variou s amounts of ruthenium, in order to examine the growth character of the dep osits in the submonolayer regime of the deposition.