Electrochemical reactions on iron silicide electrodes in alkaline solutions

Abstract

The electrochemical behaviour of 1. (i) mined iron silicide with a nominal composition of FeSi 2 (SIDBEC-DOSCO Mines) 2. (ii) pure FeSi 2 3. (iii) FeSi 4. (iv) EBONEX electrodes has been examined in KOH solutions over a wide range of cathodic and anodic potentials. The potentiodynamic profiles exhibit a structureless hysteresis and thence shed no light on the possible pseudo-faradaic processes that might be involved. Potentiostatic steady-state curves for the hydrogen evolution reaction (h.e.r.) show that the h.e.r. can be carried out at these electrodes at very high rates without affecting their electrochemical stability; overpotential values observed are quite appreciable, however. On the anodic side, oxide growth, rather than the evolution of oxygen, is the favoured process. Also, little activity is detected, at low electrode potentials (<3 V), for the anodic oxidation of HCOO −, CH 3COO −, CH 3OH, NH 2-NH 2 and Cl −. When the electrochemical reactions are forced at high rates through a galvanostatic arrangement, oxide growth to very high electrode potentials is indicated in all solutions except those containing chloride ions which exhibit a linear ‘Tafel region’ around 5.0 V ( vs Hg HgO ) presumably associated with the chlorine evolution. The mined FeSi 2 electrodes exhibit the highest electrochemical activity probably because of the presence of some chromium (~ 2%) as an impurity. All iron suicide surfaces, in general, appear to be better electrocatalysts for the cathodic and anodic reactions than the commercially-available EBONEX.