A NB-DOPED TIO2 SEMICONDUCTOR PH SENSOR FOR USE IN HIGH-TEMPERATURE AQUEOUS-SOLUTIONS

A semiconductor pH sensor using a Nb-doped TiO2 single crystal has been developed for pH measurement in high temperature aqueous solutions. The pH response of this sensor is based on the pH-dependent change in the flatband potential, EFB, of semiconductor electrode. The value of EFB can be obtained by measuring the Mott-Sehottky plot on the semiconductor electrode in a solution. The measurement of the plots has been done on Nb2O5-doped TiO2 single-crystal electrodes with different doping levels in solutions having various composition and pHs at temperatures in the range 298–523 K. It was found that the plots measured using the 0.01 mass percent Nb2O5-doped electrode at a frequency of 10 Hz had good linearity under all experimental conditions used and the relationships between the values of EFB and the solution pHs showed straight lines with the Nernstian slopes (−2.303 RT/F). The pH of pure water at temperatures up to 523 K could be measured by this electrode. The pH response of the sensor was fast, stable, and not affected by redox systems in the solutions. Interfering effects were observed, however, at higher K+ and Na+ concentrations. © 1990, The Electrochemical Society, Inc. All rights reserved.