Investigation of Fe(II)/Fe(Hg) system in thiocyanate media by cyclic and stripping voltammetry with hanging mercury drop and mercury film electrodes

Abstract

The processes of reduction and reoxidation of iron(II) ions in thiocyanate media have been investigated by cyclic and stripping voltammetry. Comparative studies with the use of hanging mercury drop electrode (HMDE), mercury film electrode (MFE) and glassy carbon electrode (GCE) have enabled us to elucidate the complex character of the processes investigated. In neutral thiocyanate media the reduction of iron(II) ions gives two peaks and one of these peaks is catalytic in nature. It has been established that iron reduced in a catalytic prepeak stays on the electrode surface while iron deposited in the second peak (observed also in the absence of thiocyanate) penetrates under the mercury surface. The “surface deposit” is oxidized at more negative potentials in the “surface peak”. The reoxidation of “surface deposit” proceeds at less negative potentials or even does not proceed at all in the case when iron is reduced at more negative potentials. Applying the concentrating preelectrolysis the anodic “surface peak” may be observed for as low a concentration of iron(II) ion as 5×10−8 mol l−1. The prewave, corresponding to catalytic reduction of Fe(II) ion, is also observed under polarographic conditions, but in this case it appears in a much narrower concentration range of thiocyanate.