ELECTROCHEMICAL-BEHAVIOR OF OXOCARBONS ON SINGLE-CRYSTAL PLATINUM-ELECTRODES .2. CROCONIC ACID OXIDATION ON PT(S)-[N(100)X(111)] SURFACES IN 0.5 M SULFURIC-ACID MEDIUM

The electrochemical behaviour of croconic acid at platinum single crys tal electrodes with Pt(100) and Pt(2n-1,1,1) orientations has been stu died in 0.5 M H2SO4 by cyclic voltammetry. Experiments with croconic a cid in solution show two main processes: the oxidation of surface pois ons at around O.8 V, and the oxidation of the acid, between 0.9 and 1. 25 V. While the currents involved in the first process tend to increas e with the terrace width, the process at higher potentials gives maxim um current density for short terraces (3-6 atoms width). Adsorption ex periments have shown that, although strongly adsorbed species are form ed from croconic acid even under open circuit conditions, the applicat ion of a polarization significantly increases the amount of poison for med. For each surface, maximum amounts of irreversibly adsorbed specie s are formed at potentials around 0.4-0.5 V. The greatest amount of st rongly adsorbed species is obtained with the Pt (100) electrode, for w hich adsorbed CO seems to be the only adsorbate. For stepped surfaces, some other intermediates may also be formed.