Electrochemical oxidation of squaric and croconic acids on Pt and Pt surfaces modified by underpotential heavy metal monolayers in acid solutions

Abstract

The electrochemical oxidation of squaric and croconic acids on platinum in aqueous perchloric acid solutions has been investigated by means of cyclic voltammetry, rotating disc electrode, potentiostatic transients and controlled-potential electrolysis. The kinetic parameters (Tafel slopes, reaction orders) have been determined on the foot of the wave by varying the sweep rate, the angular velocity, depolarizer concentration, and perchloric acid concentration. A probable mechanism has been proposed for the overall oxidation processes. It involves two charge-transfer steps followed by the desorption of product, which is the rate-determining step. The oxidation product is immediately deactivated by a rapid hydration reaction. Also, the effect of underpotential Tl, Pb, and Bi monolayers on the electrochemical behaviour of squaric and croconic acids has been examined.