SURFACE CLEAVAGE OF OXOCARBONS TO CO ADSPECIES ON PT(111) ELECTRODES INDUCED BY METAL ADATOMS

Irreversible adsorption of oxocarbons on bismuth and selenium modified Pt(lll) electrodes has been examined by cyclic voltammetry and in sit u FT-IR spectroscopy. A simple third-body effect is observed in the ad sorption of those oxocarbons giving rise to only one adsorbed residue: squaric acid which is dissociatively adsorbed to CO adsorbates and te trahydroxy-p-benzoquinone which is directly adsorbed on these surfaces . On the other hand, croconic and rhodizonic acids give rise to more t han one adsorbed residue (CO adspecies and another adsorbate with more than one carbon atom) and thus, particular effects arising from their stability can be identified, besides the third-body effects appearing at high adatom coverages. Then, bismuth ad-atoms promote the surface cleavage of croconic acid adsorbates to CO adspecies and selenium ad-a toms hinder the adsorption of some reaction intermediate involved in t he conversion of this residue to CO adspecies. FT-IR measurements rein force these voltammetric results. In the ca se of rhodizonic acids, wh ose adsorption intermediates a re CO and tetrahydroxy-p-benzoquinone, both ad-atoms promote the formation of CO adspecies, being this effect emphasized more on Pt(lll)-Se electrodes. (C) 1998 Elsevier Science S .A. All rights reserved.