ELECTROCHEMICAL-BEHAVIOR OF SQUARIC ACID ON SINGLE-CRYSTAL PLATINUM-ELECTRODES WITH BASAL ORIENTATIONS IN AQUEOUS SULFURIC-ACID MEDIUM

The electro-oxidation of squaric acid (SQA) on basal platinum single-crystal surfaces in aqueous 0.5 M H2SO4 solutions has been studied. Voltammetric results show that two different processes occur in the overall reaction. In the potential range 0.7-0.8 V vs. reversible hydrogen electrode, the oxidation of strongly bonded species formed after adsorption of SQA at less positive potentials takes place. This process is a structure-sensitive reaction and its characteristics allow us to assume that CO-like species are the stable adsorbed residues. At more positive potentials, the direct oxidation of SQA takes place overlapping with the oxidation of the platinum surface; Pt(110) is the most active electrode for this reaction. Its sensitivity to the surface structure indicates that this reaction involves the interaction of SQA molecules with the first platinum surface oxides. Only a slight inhibition effect on the direct oxidation of SQA due to strongly adsorbed CO is observed on Pt(100) and Pt(110) electrodes.