A fabrication of iridium oxide film pH micro-sensor on Pt ultramicroelectrode and its application on in-situ pH distribution of 316L stainless steel corrosion at open circuit potential

Abstract

An all solid-state pH micro-sensor has been developed using anodic electrodeposition of an iridium oxide (IrOx) film onto a 10μm platinum ultramicroelectrode. The electrochemical growth of the IrOx film was accomplished by 100 potential sweeps at 50mV/s, at different potential ranges of electrochemical deposition, followed by heat treatment at 100°C for 2h. The pH micro-sensor shows quick response to the pH variation, excellent sensitivity, stability and long lifetime in a wide pH range between 1.0 and 13.0. The slope of potential-pH response curve is found to dependent on the Ir(III)/Ir(IV) ratio of in the film, determined by XPS analysis, which is a consequence of scanning potential range during the anodic electrodeposition. The sensor has been employed to explore the localized pH distribution during the corrosion of 316L stainless steel in NaCl solution at open circuit potential and results show that localized anodic and cathodic sites on the 316L stainless steel can be accurately monitored and the pH difference between the cathodic and anodic zones increases from 0.22 to 1.27 with the prolonging of the immersion time.