Surface studies of a chalcogenide glass ferric ion‐selective electrode Part 1: Influence of ferric and hydroxide ions on interfacial kinetics

Abstract

AbstractX‐ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry (SIMS), scanning electron microscopy (SEM) and in situ electrochemical impedance spectroscopy (EIS) have been used to characterize the interfacial chemistry of the chalcogenide glass ferric (FeIII) ion‐selective electrode (ISE). The effects of ferric ions (Fe3+) and hydroxide ions (OH−) on the FeIII ISE have been studied and a mechanism for their action is proposed. It has been shown that an elevated hydroxide ion concentration causes the chalcogenide glass FeIII ISE to experience accelerated corrosion. In particular, XPS detected the formation of various antimony and iron hydroxide/oxide species, whereas SIMS and SEM revealed extensive dissolution of germanium selenide from the chalcogenide glass in the presence of OH−. The EIS measurements demonstrated that the rate of charge transfer is facilitated under extreme alkaline conditions, and this is internally consistent with the XPS/SIMS results. By contrast, EIS and XPS aging studies in ferric ion solution revealed a mild passivation film symbolic of an oxide layer. Extended aging of the chalcogenide glass membrane demonstrated a decrease in the charge transfer impedance, indicative of a breakdown in the passive layer properties. It has been shown that a charge transfer reaction occurs between Fe3+ and Ge2+ selenide sites in the membrane and that the rate of reaction is strongly dependent on temperature. Copyright © 2002 John Wiley & Sons, Ltd.