The influence of platinum (phase) oxide on the electrode kinetics of the manganese(III)/manganese(II) and cerium(IV)/cerium(III) redox couples in sulphuric acid

Abstract

The kinetics of the Ce(III)/Ce(IV) and Mn(II)/Mn(III) redox reactions (both oxidation and reduction) were followed at a rotating Pt disc electrode, on which known amounts of platinum oxide (type II) had been formed. Oxide film inhibits both anodic and cathodic reactions, but to different extents. There is no systematic decrease in i 0 with increase in film thickness suggesting that electron tunnelling is unimportant under these conditions but that electron exchange takes place with the oxide itself. The inhibiting effect of type II oxide is seen even when it is present in sub-monolayer amounts, and this and other effects suggest that the overall behaviour of the system cannot be simply represented, for example in terms of a semi-conducting oxide.