ELECTROCHEMICAL STUDY OF AUTOCATALYTIC BISMUTH(III) REDUCTION WITH TI(III)-COMPLEXES

It was first established that Bi(III) can be reduced by Ti(III) comple xes in an autocatalytic mode and that the main features of the process can be interpreted in terms of pure electrochemical mechanisms. The e lectrochemical parameters of partial reaction coupling, which could be easily changed by means of the Bi(III) and Ti(III) ions complexation, govern the possibility of the process as well as its rate and the nat ure of the product formed (continuous film or stable sol). For the pro cess to proceed it is necessary that not only the thermodynamic condit ion be met, but that the kinetic hindrances for the reductant oxidatio n be eliminated and these are realized when electroactive protonated T i(III) complexonates are formed. The rate of Bi deposition onto the co nductive surface in the acid medium is controlled by the partial react ion mixed current j(mix) and is independent of Delta E(dep) = E(Bi(III )/Bi) - E(Ti(IV)/Ti(III)), while the solution stability depends mainly on the Delta E(dep) and is independent of j(mix).