A study of the deposition of iron on mercury and glassy carbon electrodes

Abstract

The processes of reduction and reoxidation of iron(II) in thiocyanate, chloride and perchlorate media have been investigated by cyclic voltammetry and chronopotentiometry on mercury (HMDE) and glassy carbon (GCE) electrodes and interpreted as follows. On mercury electrodes, iron deposited from aquo and chloride complexes of Fe(II) is wetted by mercury and penetrates into the bulk of the electrode. On the other hand, FeS formed during the electroreduction of thiocyanate complexes of Fe(II), is adsorbed on the electrode surface and makes the wetting of iron by mercury impossible. Consequently, the iron stays on the electrode surface and accelerates the process of hydrogen evolution. This, in turn, leads to alkalization of the solution and to precipitation of Fe(OH) 2 in the pre-electrode layer. Subsequently, both FeS and Fe(OH) 2 catalyze the formation of metallic iron on the mercury surface. FeS and Fe(OH) 2 are also formed in the surface layer during the reduction of thiocyanate complexes of Fe(II) on the GCE. In practice, neither substance participates in the initiation of iron settling on the glassy carbon surface, but their influence on the electrode processes of systems examined on the GCE is significant.