Electrochemical behaviour of mixtures of VO +2 and H2O2 in 1 M HClO4 on mercury and platinized platinum

Abstract

The electrochemical behaviour of mixtures of VO⁺₂ and H₂O₂ in perchloric acid media was studied both on platinized platinum and on mercury. From voltammetric measurements on platinized platinum it was possible to show that within a definite potential range (from 0.94 to 0.44 V/S.C.E.) the electroreduction of VO(O₂)⁺ to VO²⁺ and H₂O as well as its electro-oxidation to VO⁺₂ and O₂ are preceded by the homogeneous decomposition of the VO(O₂)⁺ ion: VO(O₂)⁺+ H₂O[graphic omitted]VO⁺₂+ H₂O₂. The rate constant ρ= 0.74 s^–1.

The polarographic behaviour of VO(O₂)⁺ at a dropping mercury electrode in the presence of an excess of H₂O₂ is characterized by the decomposition of this ion according to the preceding equation, followed by the electroreduction of VO⁺₂ to VO²⁺ and by the subsequent chemical regeneration of VO(O₂)⁺ from VO²⁺ by hydrogen peroxide. The regeneration reaction was shown to be first-order with respect to VO⁺₂ and second-order with respect to H₂O₂; its rate constant is 1.18 × 10³ l.² mol^–2. s^–1.