Electrochemical behaviour of iron in alkaline sulphide solutions

Cyclic voltammograms and galvanostatic polarisation curves were traced for the iron electrode in alkaline solutions containing sulphide species. In sulphide free NaOH solution, the galvanostatic anodic polarisation curves are characterised by two well defined steps before tending finally to values characteristic for the oxygen evolution reaction. However, using cyclic voltammetry technique, three anodic peaks are distinct. On the other hand, the cathodic half cycles using both techniques are characterised by two cathodic reduction steps before hydrogen evolution commences. In the presence of increasing sulphide content the polarisation curves are characterised by the presence of several anodic and cathodic regions. The anodic regions correspond to the simultaneous formation and oxidation of different Fe sulphide and oxide species. A mechanism is thus proposed for the formation and reduction of iron sulphide species.