ELECTROCHEMISTRY OF PLATINUM SINGLE-CRYSTAL SURFACES .2. STRUCTURAL EFFECT ON FORMIC-ACID OXIDATION AND POISON FORMATION ON PT(111), (100) AND (110)

The geometrical arrangement of sites favorable for formic acid oxidation and the poison formation reaction is determined by using low index platinum single crystal planes. For this determination, the least number of sites required for the reactions to occur, which was obtained in the study of electrocatalysis by adatoms, was used, that is, three adjacent sites are required for formic acid oxidation and four adjacent sites are required for poison formation. The triplet of sites on a unit lattice of Pt(111) and that on a unit lattice of Pt(100) plane are equally very favorable for the main oxidation reaction, but that on a unit lattice of Pt(110) is not so favorable as those on the former two planes. The oxidation rate is more than one order of magnitude lower on the latter than on the former triplets. The poison formation reaction proceeds at a very high rate on the (100) and the (110) planes.