Description du sujet de thèse

State of the art: Since the 2000s, proton-conducting ceramic oxides have attracted increasing interest. The operation of these cells, called Protonic Ceramic electrochemical Cells (PCCs), is based on the proton conduction of a ceramic electrolyte in the temperature range of 400 – 600°C. In this temperature range, thermodynamic efficiencies are comparatively higher than at low temperatures and the aging of the materials is relatively moderate due to a lower operating temperature than in other anionically conductive systems. AMO3-type compounds (A = Ba, Sr; M = Ce, Zr, perovskite structure) are the most studied materials currently in the field of PCC electrolytes. In these compounds, the substitution of the metal cation M by a trivalent cation (Y, Yb, Gd, In, Sc, etc.) makes it possible to enhance the diffusion properties of hydrogen within the crystal lattice of the material. To date, BCZY-type compounds with the chemical formula BaCe0.9-xZrxY0.1O3-δ exhibit the best proton conductivity properties at 600°C among perovskite structure oxides. Subject: The work carried out during this doctorate will be based on the PVD deposition skills of the FEMTO-ST institute and on the high-temperature electrochemical characterization skills of the DLR. The performance and qualities of the cells will be determined by complex impedance measurement and electrochemical tests in single-cell mode. Three main aspects will be addressed. The first will concern the development of the best sequence for producing PCC cells from standard materials using Tape Casting, Screen printing, Spray deposition techniques at the electrode level provided by the HADES project consortium and PVD mastered by the FEMTO-ST institute at the ionic conductor level. This will involve preparing 25 mm diameter button cells, called generation 1, then moving on to the scaling stage to reach a diameter of 50 mm or square cells of 50 mm x 50 mm. Sintering and heat treatment sequences will be developed in accordance with the production sequence to obtain a suitable architecture: dense electrolyte and porous electrodes with good quality interfaces. Particular attention will be paid to the interdiffusion phenomena inherent in the production of these cells. The second part will focus on the manufacturing of generation 2 cells developed with materials and architectures determined by the chemical partners of the HADES project. The shaping and heat treatment sequence developed for generation 1 cells will allow for faster optimization of generation 2 cells. Finally, the third part will consist of conducting electrochemical tests under real operating conditions on the most relevant structures for electrochemical hydrogen pumping applications (so-called symmetrical cell architecture) and/or electrolysis (asymmetrical cell architecture), in particular by carrying out long-term tests of several hundred hours which are well mastered by the DLR, and to carry out a performance diagnosis using characterization methods such as electrochemical impedance spectroscopy and associated simulation tools (Distribution of Relaxation Times & Equivalent Circuit Modeling). During these three study phases, structural and microstructural characterizations will be conducted before and after the electrochemical tests.

Contexte de travail

In the context of the energy transition, the use of hydrogen as a vector appears to be an essential solution. Systems using proton-conducting ceramic materials will occupy a leading position due to their high operational flexibility and high efficiency. As part of the Franco-German call for projects of May 6, 2024, entitled "Development of the hydrogen pathway for the future energy mix," supported by the ANR and the BMBF, one of the five selected projects focuses on the fabrication of electrochemical cells based on proton-conducting ceramic materials for the production of hydrogen from the decomposition of renewable ammonia. This thesis, jointly funded by the FEMTO-ST Institute and the German Aerospace Center (DLR) in Stuttgart, is part of this project, whose acronym is HADES (Hydrogen through Ammonia Decomposition from Energy Storage).

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