In-situ electrochemical scanning tunneling microscopy studies on the oxidation of iron in alkaline solution

Abstract

In situ electrochemical scanning tunneling microscopy (ESTM) was used to study the process of iron oxidation in alkaline solution. Images of the iron surface were taken at a potential of −1350 mV ( Ag AgCl ) after cycling to different more positive potentials. It was shown that there is a correlation between the surface structure and electrochemical reactions occurring at potentials corresponding to different anodic peaks on a cyclic voltammogram. It was found that sweeping to the potential of −1100 mV, corresponding to the appearance of the first anodic peak on the cyclic voltammogram, caused no noticeable reconstruction of the electrode surface. Cycling to the potential of −950 mV, corresponding to the potential range of the second anodic peak, results in a roughening of the iron surface and formation of features characteristic of crystallographic etching. Sweeping to more positive potentials leads to smoothing of surface due to oxidation-reduction reactions of the surface. These results provide support to the interpretation of the first anodic peak on the cyclic voltammogram as oxidation of adsorbed hydrogen, and the second peak as an active-passive transition followed by formation of the passive oxide layer.