ADATOM COVERAGE STUDIES DURING THE CATALYSIS AND INHIBITION OF FORMIC ACID ELECTROOXIDATION BY UNDERPOTENTIAL DEPOSITION.

The catalysis and inhibition of formic acid electrooxidation as a result of metal submonolayer formation on polycrystalline platinum were studied quantitatively using the rotating ring-disk electrode technique. Under controlled flux conditions one can approach limiting current behavior for the oxidation of formic acid and thereby determine the upper limit for the optimum adatom coverage for lead and bismuth. These values are found to be 25%-35% of the platinum electrode real area. The experiments in this paper are correlated with the literature dealing with polycrystalline and single-crystal studies of hydrogen adsorption and formic acid oxidation to explain differences for the electrocatalytic behavior of various underpotential deposited (UPD) species. Bismuth, lead and other UPD species with radii larger than platinum do deposit significantly on Pt(100) at low UPD coverages, and can therefore slow the poisoning of the formic acid oxidation process on this plane.