ELECTROCHEMICAL-BEHAVIOR OF OXOCARBONS ON SINGLE-CRYSTAL PLATINUM-ELECTRODES .4. RHODIZONIC ACID IN 0.5-M SULFURIC-ACID MEDIUM

The electrochemical behaviour of rhodizonic acid on Pt(111), Pt(100) a nd Pt(110) surfaces has been studied in sulphuric acid solutions by cy clic voltammetry and in situ FTIR spectroscopy. The direct oxidation p rocess takes place at potentials positive to the desorption of strongl y bonded adsorbates. For the three orientations, polyketonic compounds and finally carbon dioxide are the oxidation products. Reduction proc esses can cake place at lower potentials, leading to the formation of tetrahydroxyquinone and hexahydroxybenzene, also detected by FTIR. The se species seem to be adsorption intermediates in the case of Pt(111), transforming from one to another depending on potential. A small amou nt of carbon monoxide is observed on this orientation. Significantly h igher CO adsorptions have been obtained for Pt(110) (linear CO) and Pt (100) (linearly and bridge bonded). Other adsorbates seem to be formed after adsorption experiments, which give no detectable infrared absor ption.