Electrocatalysis of the Anodic Oxidation of As(III) On Platinum and Other Noble-Metal Electrodes

摘要

Primarily, platinum is used as the electrode material, but the reaction also is studied in gold, iridium and palladium electrodes. Potentiostatic and potentiodynamic experiments at rotating disc electrodes are described. Conventional and transient rotating ring-disc experiments also are utilized. A relatively new technique, sinusoidal hydrodynamic modulation at a rotating disc electrode, is applied to the study of As(III) oxidation; this technique permits the examination of the reaction in the O sub 2 evolution region. The oxidation of As(III) occurs at a rate less than the mass-transport limited rate. It is shown that the overall rate is limited by a heterogeneous reaction that does not involve charge transfer. The heterogeneous rate constant k of the rate-determining step is evaluated for a series of times and applied potentials. A mechanism for the oxidation of As(III) on platinum is proposed that has as its central feature a rate-determining surface reaction between an adsorbed As(IV) specie and an adsorbed hydroxyl radical. The electrochemistry of arsenic and the anodic oxidation of platinum, gold, iridium, and palladium are reviewed in detail. Additionally, a literature review of anodic reactions on noble metals in which direct participation of the oxide has been proposed is presented. (ERA citation 09:017013)