A ring-disk electrode study of the current/potential behaviour of platinum in 1.0 M sulphuric and 0.1 M perchloric acids

The production of small amounts of soluble species during the oxidation and reduction of a platinum electrode in 1 M H₂SO₄ and 0.1 M HClO₄ has been established using the rotating ring-disk electrode. Pt(II) is produced when an oxidized platinum electrode is reduced. The potential range for the formation of Pt(II) corresponds to that predicted on thermodynamic grounds for the reduction of PtO₂. An unidentified species is produced during the oxidation of the platinum electrode. This species undergoes a first order homogeneous decomposition with a rate constant of 27 s^-1 (mean value for both acids). Repeated potential cycling (5 or more times) of a platinum electrode in 1.0 M H₂SO₄ between 0.2 and 1.2 V (sce) results in a reproducible current/potential curve, for which 50 μC/cm² more charge is required on the anodic cycle than during the cathodic cycle. The soluble products detected at the ring electrode account for 6 μC/cm² of the excess anodic charge at the disk electrode.