The electrochemistry of the nickel sulfides. I. NiS

The electrochemical behaviour of NiS (synthetic millerite) is examined by cyclic voltammetry and coulommetry at rotating disc and ring-disc electrodes. In contrast to a previous study, the passive layer on NiS is shown to be a mixture of sulfur and a nickel-deficient nickel sulfide. This layer is shown to be conductive to electrons but not to nickel ions. The formation of an insulating layer of elemental sulfur at higher potentials is demonstrated, while rapid dissolution of the mineral to form Ni2+(aq) and oxy anions of sulfur is observed at greater than + 1 V (s.c.e.).