Effects of thiocyanate on Ni(Hg)/Ni(II) and Ni/Ni(II) electrode reactions

Abstract

Chronopotentiometric and stationary polarization measurements have been performed on mercury, nickel, and platinum electrodes in aqueous solutions of x M NiCl2+y M KSCN+(1−2x−y) M KCl at 25°C. Reaction products have been studied by electrochemical, radio-tracer, electron-microprobe, and X-ray diffraction techniques. At all three electrodes, cathodic reduction mostly gives a composite film of amorphous nickel sulphide and small nickel crystals. At mercury, however, this is preceded by the formation of a superficial layer of partly supersaturated nickel amalgam. Thiocyanate stimulates the charge transfer at this liquid amalgam and provides sulphur for the sulphide precipitation, but has little effect on the reactions at nickel crystals. The stimulation is more likely to be due to specific adsorption than to complex formation. Ni(I) appears as intermediate.