Electrochemical Response of Sr(Ce0.9Zr0.1)0.95Yb0.05O3-α high-Temperature Hydrogen Sensors
Authors: Hinojo Antonio , Pallarès Enric , Colominas Sergi , Abella Jordi 
Published: July 2021

In future fusion reactors, tritium and deuterium will be used as a primary fuel. Currently, the most important research and development project about nuclear fusion energy is ITER (International Thermonuclear Experimental Reactor). To produce the fusion reaction, tritium will be generated inside the core using a breeding blanket. One of the suggested blankets is based on the use of molten lithium–lead eutectic alloy (Pb-15.7Li) [1]. This blanket will be flowing around the reactor core and while the fusion reaction occurs, energy is released and collected with an external heat exchanger system.
Due to its short half-life (12.3 years), there are not natural tritium sources. Therefore, it must be obtained in situ and continuously in the breeding blanket. This hydrogen isotope can be produced by bombarding lithium with fast neutrons, which escape from the generated and confined plasma in the toroid-shaped vacuum chamber of a tokamak, to yield tritium and helium (6Li + n → 4He + 3H + 4.8MeV) [2]. Hence, dynamic tritium concentration measurement is of major interest for nuclear fusion reaction engineering and experimental proof of tritium self-sufficiency in liquid metal breeding systems. Consequently, it is necessary a measuring system that allows determining tritium concentration in high-temperature conditions.
Electrochemical sensors based on solid-state proton conductor ceramics can be used for that purpose. These materials have attracted significant interest because of their chemical and physical durability, especially at elevated temperatures. These electrolytes are perovskite-type materials with electrical carriers, positive holes, excess electrons, oxide ion vacancies, and interstitial protons, which interact with oxide ions. Under this approach, new methods of synthesis are being studied in order to obtain ceramic materials of higher quality and purity able to offer better measurement signals.
In the present work, the proton-conducting perovskite Sr(Ce0,9-Zr0,1)0,95Yb0,05O3-α was synthesized by two different methods. On one side, a conventional sol-gel method, using citric acid as a complexing agent, was employed [3]. On the other hand, the second method used was the glycine method, which is based on the combustion of glycine with the precursor's nitrates. Using the glycine method, it could be obtained a ceramic porous foam that improved the sintering process. Both synthesized materials were characterized using X-Ray Diffraction and SEM-EDS analysis.
Finally, the obtained ceramic materials were properly sintered and shaped in order to construct electrochemical hydrogen sensors. Amperometric measurements were performed at 500°C and 600°C using different hydrogen concentrations and the response of the two sensors was compared.
References
[1] E. Mas de les Valls, L.A. Sedano, L. Batet, I. Ricapito, A. Aiello, O. Gastaldi, F. Gabriel, Lead-lithium eutectic material database for nuclear fusion technology, J. Nucl. Mater. 376 (2008) 353–357, https://doi.org/10.1016/j.jnucmat.2008.02.016

[2] H. Mei, Q. Wu, J. Chen, B. Zhang, Y. Liu, Equivalent determination of tritium production in liquid blanket of fusion reactor using lithium isotopic abundance analysis, Fusion Eng. Des. 112 (2016) 89–92, https://doi.org/10.1016/j.fusengdes.2016.07.015

[3] E. Juhera, S. Colominas, J. Abellà, Amperometric hydrogen sensors for application in fusion reactors, Fusion Eng. Des. 124 (2017) 901–904. https://doi.org/10.1016/j.fusengdes.2017.01.049