High temperature and pressure chemical sensors based on Zr/ZrO2 electrode prepared by nanostructured ZrO2 film at Zr wire

A Zr/ZrO2 oxidation electrode was fabricated for in situ measurement of pH values of high temperature aqueous solutions. Combined with a Ag/AgCl reference electrode, the Zr/ZrO2 sensor responded rapidly and precisely to the pH of the solutions over a wide range of temperatures. The Zr/ZrO2 electrode was made by oxidizing Zr metal wire with a Na2CO3 melt to produce a thin film of ZrO2 on the Zr wire surface. The nanostructure of the ZrO2 thin film was characterized using high-resolution transmission electron microscopy (HRTEM) observations. The nature of the nanostructured ZrO2 thin film on the Zr of the Zr/ZrO2 electrode plays a vital role in the construction of Zr/ZrO2 chemical sensors, particularly when the electrode is utilized for in situ measurement of the electrochemical parameters of aqueous solutions at high temperatures and pressures.Chemical analyses of the ZrO2 thin films revealed that the Zr/ZrO2 interface is divided into five zones from the outermost zone to the center: (1) prismatic and oxygen-rich ZrO2 zone; (2) ZrO2; (3) oxygen-rich Zr; (4) oxygen-bearing Zr; and (5) Zr metal. Especially, the outermost oxygen-rich ZrO2 zone of the films is composed of nanometer-sized monoclinic crystals.