Solvent effect on the rate of metal deposition reactions: Investigations of the kinetics of Ni(II) discharge at the mercury in mixed water methanol solvents

The kinetics of Ni²⁺ deposition at the mercury electrode, from non-complexing electrolytes in mixed water methanol solvents has been investigated. The rate of this reaction, in the whole composition range, at large overpotentials is controlled by a limiting “chemical” process. The rate constants of the limiting process when plotted as a function of the solvent composition display a relationship similar to those observed for the large organic, bidendate ligands substitution reactions, believed to the controlled by the Ni(II)-solvent bond rupture. Hence, the limiting “chemical” process in Ni²⁺ discharge can be identified as the slow solvent dissociation step. These results confirm the mechanism of Ni²⁺ dischrage already proposed by Gierst and Dandoy on the basis of investigations performed in aqueous solutions.