POISON FORMATION REACTION FROM FORMIC-ACID AND METHANOL ON PT(111) ELECTRODES MODIFIED BY IRREVERSIBLY ADSORBED BI AND AS

Dissociative adsorption of formic acid and methanol on adatom-modified Pt(111) electrodes has been carried out as a way of studying poison f ormation reactions on these surfaces. The electrodes were prepared usi ng irreversible adsorption of Bi and As. A modification of the dissoci ative adsorption technique used for poison formation studies has been employed. For clean Pt(111) surfaces the behaviour of the poison forma tion reaction of the two organic molecules is almost the same, but on adatom-modified Pt(111) electrodes different results are found. Bi and As show an important long-range electronic effect which inhibits pois on formation from the dissociative adsorption of formic acid at very l ow adatom coverage. However, for methanol, the inhibition due to the p resence of Bi adatoms on the surface can be explained by a simple thir d-body effect. A computer simulation of the dissociative adsorption of formic acid on Bi-modified Pt(111) electrodes has been carried out in order to calculate the width of the domains affected by the presence of Bi adatoms.