Electrochemical behaviour of vanadium compounds at a carbon paste electrode

The behaviour of a variety of vanadium compounds (NaVO3, V2O5, V2O4, VOSO4 . 5H(2)O and VOCl2) at a carbon paste electrode has been investigated by cyclic voltammetry, chronopotentiometry and chronoamperometry, using hydrochloric acid and perchloric acid as electrolytic binders. The experiments revealed the occurrence of two different systems where the dissolved fraction was that involved in charge transfer processes. The reduction processes observed were the conversions V(V) --> V(IV) and V(IV) --> V(II), whereas the oxidation processes involved were V(II) --> V(III), V(III) --> V(IV) and V(IV) --> V(V). Additional anodic and cathodic peaks were obtained when hydrochloric acid was used as electrolyte; reduction peaks were demonstrated to involve solid species and chloride ions in the charge transfer process. The influence of electrolyte concentration and scan rate on the behaviour of the electrode and the redox systems of vanadium have been investigated and plausible electrodic mechanisms are discussed. (C) 1997 Elsevier Science S.A.