Proton conducting ceramics for potentiometric hydrogen sensors for molten metals

Tritium monitoring in lithium-lead eutectic (Pb-15.7Li) is of great importance for the performance of liquid blankets in fusion reactors. Also, tritium measurements will be required in order to proof tritium self-sufficiency in liquid metal breeding systems. On-line hydrogen (isotopes) sensors must be design and tested in order to accomplish these goals. Potentiometric hydrogen sensors for molten lithium-lead eutectic have been designed at the Electrochemical Methods Lab at Institut Quimic de Sarria (IQS) at Barcelona and are under development and qualification. The probes are based on the use of solid state electrolytes and works as proton exchange membranes (PEM). In this work the following compounds: BaZr_0.9Y_0.1O₃, BaCe_0.6Zr_0.3Y_0.1O_3-α, Sr(Ce_0.6-Zr_0.4)_0.9Y_0.1O _3-α and Sr₃Fe_1.8Co₂O ₇ have been synthesized in order to be tested as PEM H-probes. Potentiometric measurements of the synthesized ceramic elements at 500 C have been performed at a fixed hydrogen concentration. The sensors constructed using the proton conductor elements BaZr_0.9Y_0.1O₃, BaCe_0.6Zr_0.3Y_0.1O_3-δ and Sr₃Fe_1.8Co_0.2O_7-δ exhibited stable output potential and its value was close to the theoretical value calculated with the Nernst equation (deviation around 60 mV). In contrast, the sensor constructed using the proton conductor element Sr(Ce_0.6- Zr_0.4)_0.9Y_0.1O_3-δ showed a deviation higher than 100 mV between experimental an theoretical data.