Desolvation step preceding electroreduction and the electrochemical reactions of the Ni(II)/Ni(Hg) system in dimethylformamide (DMF) and its mixtures with water

The kinetics of the electrode reaction of the Ni(II)/Ni(Hg) system in DMF and its mixtures with water at different concentrations of several background electrolytes has been studied.

Similarly to aqueous solutions, at higher background electrolyte concentrations the charge transfer step is preceded by a chemical reaction. It was deduced that this proceeding reaction is due to slow dissociation of the solvent molecule in the S¹_N process.

The change of a solvent from water to 70 vol.% of DMF decreases the standard rate constant (k_s) for about one order of magnitude. At larger DMF content k_s is virtually independent of the solvent composition. The change of k_s with the DMF content was explained by assuming the resolvation of Ni(II) ions at the electrode surface in proportion to the surface coverage of the electrode molecules of both solvents.