Selective effect of supporting electrolyte on the polarographic catalytic current of nickel(II) in acetonitrile in the presence of halide ions

Abstract

An acetonitrile solution of nickel(II) in the presence of halide ion gives a catalytic pre-wave. The pre-wave height was studied as a function of the concentration of nickel(II) and halide ions. The catalytic activity of halide ion for the pre-wave in lithium perchlorate solution decreases in the following order: iodide, bromide, chloride ions; on the other hand, in a quaternary ammonium perchlorate solution it decreases in the order: chloride, bromide, iodide ions. A mechanism which involves adsorption equilibria between bulk and adsorbed halide ion and the cation of the supproting electrolyte, and a complexation reaction of nickel(II) and adsorbed halide ions, is presented. The cation effect on the catalytic polarographic current is discussed on the basis of the selective passing of halide ion through holes in the adsorbed, layer of the cation of the supporting electrolyte.