On the onset of current oscillations at the limiting current region emerged during iron electrodissolution in sulfuric acid solutions

Abstract

The onset of current oscillations emerged at the limiting current region (LCR) during iron electrodissolution in sulfuric acid solutions is investigated in this work by using a number of perturbation experiments. Perturbation experiments on the Fe| n M H 2SO 4 system were conducted through the: (a) insertion of a series external resistance, (b) rotation of the Fe-disc electrode, (c) injection of various chemical species on the Fe surface and (d) change of the position of the Fe electrode. Electrical, mass-transport and chemical effects, all were found to influence the onset of current oscillations. These effects were combined with previously developed ideas concerning the formation of a ferrous salt layer along with the partial passivation of the Fe electrode. A plausible mechanism is proposed, able to explain the onset of current oscillations at the beginning of the mass-transfer controlled LCR. This mechanism agrees with experimental observations and may explain: (i) why current oscillations emerge within a fixed potential region at the LCR, (ii) why the IR-drop along with appropriate hydrodynamic conditions are both required for the onset of oscillations and (iii) what is the role of hydrodynamic conditions and chemical composition of the layer formed at the LCR.