Fabrication of thick film sensitive RuO2-TiO2 and Ag/AgCl/KCl reference electrodes and their application for pH measurements

Abstract

In this work thick film potentiometric and conductimetric sensors based on mixed metal oxides RuO2 and TiO2 were fabricated and investigated. For potentiometric sensors, pH sensitive RuO2-TiO2 electrode and a reference Ag/AgCl/KCl electrode were developed and deposited on an alumina substrate by screen printing method. For conductimetric pH measurements, the sensitive RuO2-TiO2 paste was screen printed on the surface of an interdigitated conducting electrode. The results of the potentiometric, impedance spectroscopic, SEM, EDS, XRD and XPS studies of the fabricated sensors were presented and discussed. The thick film pH sensor with both the reference and sensitive electrodes screen printed on the same alumina substrate shows a sensitivity of 56.11mV/pH, close to the theoretical value, a very fast response shorter than 15s, long lifetime and reusability. Its applicability for measurements of pH of water was confirmed. The electrochemical impedance spectroscopy method was used for characterization of the properties of the sensitive RuO2-TiO2 film in a frequency range of 10Hz–2MHz. The sensor conductance was found to show a linear dependence on the pH value in the range of 4–11. Comparison of X-ray photoelectron spectra of the sensors before and after treatment in various solutions revealed some differences in surface composition dependent on pH value. The cost of the fabricated thick film pH sensor was significantly reduced by using for the sensitive electrode besides RuO2 a much cheaper second oxide TiO2, and due to a simple method of the reference electrode preparation.