Mixed-potential Behavior of Nanostructured RuO[sub 2] Sensing Electrode of Water Quality Sensors in Strong Alkaline Solutions at a Temperature Range of 9–30° C

Abstract

Mixed‐potential behavior of the water quality monitoring sensors using nanostructured RuO2 sensing electrode (SE) has been observed in strong alkaline solutions at dissolved oxygen (DO) measurements in the temperature range of 9–30° C. This behavior indicated that a Faradaic oxygen reduction reaction becomes not only a one‐electron process, which is typical for DO measurements at a neutral pH, but rather multi‐step process with superoxide oxygen ions (O2−), OH− and RuO42− ions involvement. The DO sensing characteristics were examined in the pH range of 2.0–13.0. The measured emf at strong alkaline solutions is a mixed potential from the reactions involved RuO42− and OH− ions and DO. Impedance spectroscopy was employed for confirmation the mixed‐potential behavior of the sensor. It was also found during experiments that OH− ions influence the response/recovery rate of the SE reactions as the pH of water increases.