Effect of Oxidization Temperatures and Aging on Performance of Carbonate Melt Oxidized Iridium Oxide pH Electrode

• Published in: Sensors (Basel, Switzerland) Vol. 19; no. 21; p. 4756
• Main Authors: Wang, Penggang, Guo, Tengfei, Zhao, Tiejun, Du, Zhenxing, Jin, Zuquan, Dong, Biqin, Li, Zhe
• Format: Journal Article
• Language: English
• Published: Basel MDPI AG 01.11.2019; MDPI
• Subjects: Atomic force microscopes; Atomic force microscopy; carbonate melt oxidized; Cement hydration; Chemical composition; Electrodes; Glass substrates; Investigations; iridium oxide; Metal oxides; Methods; Microscopy; microstructure; Morphology; Oxidation; oxidation temperature; Oxide coatings; ph electrode; Photoelectrons; Reinforced concrete; Response time; Silicon nitride; Wire; X ray photoelectron spectroscopy; China
• ISSN: 1424-8220; 1424-8220
• DOI: 10.3390/s19214756

Iridium oxide pH electrodes employing the carbonate melt oxidation method were fabricated with oxidation temperatures of 750 °C, 800 °C and 850 °C, respectively. Scanning electron microscope (SEM) and atomic force microscope (AFM) images showed that the oxide film regularized with the increase in oxidation temperatures. The pH response, response time and long-term stability of the electrodes indicated that the electrodes made at 850 °C had the best performance. X-ray photoelectron spectra (XPS) surveys investigated the change in the electrodes’ chemical composition and element oxidation states at 850 °C, and the results showed that the relative content of Ir3+ had increased by 23.9%, and the Ir4+ and Ir6+ had decreased by 10.9% and 13%, respectively, in the surface oxide layer after one month of aging. However, the relative contents of Ir3+, Ir4+ and Ir6+ were almost constant for the inner oxide layer. Meanwhile, the XPS result also indicated that the outer oxide layer of the electrode had a higher hydration degree than the inner oxide layer.