Quasi-simultaneous electrochemical/chemical imaging of local Fe2+ and pH distributions on 316 L stainless steel surface

Abstract

Micro-spatial chemical information over the corrosion metal surface detected with conventional single-tube amperometric or potentiometric microelectrodes is relatively single in SECM. In this paper, we investigate a novel all solid-state dual function Pt-Pt/IrOx ultramicroelectrode (UME) for the electrochemical/chemical visualization of the corrosion process of 316 L stainless steel at open-circuit potential in a 6.0% FeCl3 solution using both amperometric and potentiometric modes of SECM. For the same solution, without further changes, we performed quasi-simultaneous probe-imaging of the localized Fe2+ concentration for dissolved metal-ions at the local anodes, including pH changes due to the consumption of protons at the local cathodes. Local anodic and cathodic active sites were detected repeatedly at the same position in all images, which is consistent with SEM results, evidenced the formation of stable pit over the 316 L-SS surface. In addition, line scans extracted from the current and pH scan images distinctly display the apparent distance between local anodic current- and cathodic pH- peak sites is approximate 84 μm, with a height of 15 μm height during 12 h immersion. This sensor is of pivotal importance in future studies of micro-spatial chemical environment at solid-liquid interface.