Catalytic polarographic current of nickel(II) in acetonitrile in the presence of thiocyanate ions

Abstract

The effect of thiocyanate ion on the electrode reaction of nickel(II) in acetonitrile solution was investigated by d.c. polarography, i-t curve analysis, a.c. polarography and controlled potential electrolysis. In the presence of thiocyanate ion, nickel(II) exhibited a catalytic pre-wave in LiClO 4 , NaClO 4 and NH 4 ClO 4 supporting electrolytes, and a catalytic maximum wave in Me 4 NClO 4 , Et 4 NClO 4 and n-Bu 4 NClO 4 . The maximum wave usually separated into two maxima. The characteristics of these maxima were studied as a function of concentration of nickel(II), LiSCN and n-Bu 4 NClO 4 . A mechanism which involves adsorption equilibria between bulk and adsorbed thiocyanate and quaternary ammonium ions, the cyclic regeneration of adsorbed thiocyanate ion for the pre-wave and the catalytic reduction of thiocyanate ion with the electroreduced active metallic nickel for the maximum wave has been presented. The characteristics of the two maxima are discussed on the basis of the difference in character of the adsorption process of thiocyanate and quaternary ammonium ions.