Electroreduction mechanism for transition metals

Abstract The similarity of the structures and of the compositions of the intermediate reduction products of such transition metals as copper, manganese, chromium, nickel, rhenium, molybdenum, tungsten and zirconium indicates that their reduction from aqueous solution takes place by the same mechanism. The presence of low valency compounds in the solid phase indicates that they exist in the cathodic zone, i.e. in the material of the cathode film which is formed as a result of the accumulation of a sufficient amount of low valency compounds of the respective metals at a given polarization value, the cathode layer being alkalized at the same time. The cathode film is a source material for a deeper reduction reaction to proceed and it serves as a barrier that separates the reaction zone from the bulk electrolyte, preventing the oxidation of low valency compounds that have already formed there. The nature of the ligand determines the rate of dissolution of incomplete reduction products formed in the cathode layer on the electrolyte side and the rate of formation of these products as a result of alkalization. These chemical reactions parallel the electrochemical reactions. The physicochemical properties of the cathode film determine the technological parameters of the electroreduction of the corresponding metal ions. The formation of real bifunctional systems makes it possible to produce functional coatings and to electrocrystallize metals with deposition potentials that are more negative than with hydrogen.