Development of Dissolved Hydrogen Sensors for High Temperature Water Systems

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For in situ measurements of the concentration of hydrogen in aqueous solutions at elevated temperatures, a newly designed hydrogen sensor, which is based on an electrochemical cell employing a yttria-stabilized zirconia (YSZ) solid electrolyte and a noble metal working electrode, has been developed. The hydrogen response of the sensor has been examined at temperatures as high as 300℃. The principal findings of this work are summarized as follows :1. YSZ oxygen sensors equipped with Ag powder or thin film electrodes were fabricated. The thin film electrodes were prepared by ion-beam-sputter (IBS) deposition. The sensors showed a fast, Nernstian response to changes in oxygen partial pressure at temperatures of 200℃ to 300℃, indicating that both the Ag powder and thin film electrodes can be used as an internal reference electrode of hydrogen sensor.2. Hydrogen sensors equipped with painted or IBS-deposited Pt and Pd were fabricated and the response to hydrogen in NィイD22ィエD2HィイD22ィエD2 gas … More mixtures was examines. The response rate in the gas mixtures was faster for sensors employing thin IBS-Pt and -Pd electrodes compared with those employing thick painted electrodes. However, the hydrogen electrode reaction in aqueous solutions was not affected by the difference in the preparation method of the electrodes. The corrosion resistance of Pt in high temperature aqueous solution was higher than that of Pd.3. Hydrogen sensors employing a YSZ tube, a Ag-OィイD22ィエD2 internal reference electrode, and a hydrogen-sensitive Pt working electrode covered with a PTFE diffusion membrane has been fabricated and the response to hydrogen in aqueous solutions was examined at temperatures over the range of 200℃ to 300℃. The sensors displayed rapid and Nernstian responses to changes in hydrogen concentration in the temperature range of 250℃ and 300℃. Oxygen in solution had little effect on the potential of the sensor, when the concentration of oxygen is lower than that of hydrogen. The potential of the sensor was independent of the solution pH. Less