Assessing tungsten-based electrodes coated with W and Ce oxides for pH sensing applications

Abstract

This study assessed tungsten-based materials with and without dispersed CeO₂ for potential use as pH sensors. Specifically, three types of tungsten electrodes were characterized: tungsten electrodes without CeO₂ but with native oxide, tungsten electrodes without CeO₂ that were oxidized, and a tungsten electrode containing dispersed CeO₂ that was oxidized, resulting in a mixture of WO₃, CeO₂, and Ce₂O₃. The characterization was performed using SEM/EDAX, X-ray photoelectron spectroscopy (XPS), and electrochemical techniques. The oxide coatings showed higher oxygen contents compared to native tungsten. XPS confirmed the presence of a thick layer of WO₃ and cerium oxides. The electrodes exhibited good reproducibility and stability in pH measurements. A linear relationship was found between the open circuit potential and pH, with slopes of 44.9, 40.8, and 46.9 mV pH⁻¹ for native oxide, WO₃, and WO₃ with CeO₂ and Ce₂O₃, respectively. The latter showed the highest sensitivity and lowest hysteresis. The response times ranged from 14.5–23.5 s and were faster in acidic solutions. Overall, the inexpensive tungsten-based electrodes demonstrated promising capabilities for pH sensing, but in particular ceriated tungsten electrodes.