Analysis of degradation mechanisms in solid oxide cells by transmission electron microscopy and atomic probe tomography

Context and problematic: High-temperature electrolysis is currently considered one of the most promising technologies for the production of low-carbon hydrogen [1]. The electrolysis reaction takes place in a solid oxide cell (SOC) in which water molecules dissociate to form hydrogen and oxygen under the action of an electric current and a supply of heat. A SOC consists of a dense electrolyte sandwiched between two porous electrodes. The hydrogen electrode (cathode) is a nickel and yttrium stabilized zirconia (Ni-YSZ) cermet in which the water reduction reaction takes place at the triple phase boundaries between the porosity and the electronic (Ni) and ionic (YSZ) conductors. The YSZ electrolyte, which is stable over a wide range of operating conditions, provides the transport of oxygen ions between the two electrodes. The oxygen electrode (anode) is typically a strontium-doped lanthanum cobalt ferrite, La_0.6Sr_0.4Co_0.2Fe_0.8O₃ (LSCF). This oxide exhibits satisfactory catalytic activity and good mixed ionic and electronic conduction. To further improve cell performance, it has recently been proposed to replace this material with a PrOx praseodymium oxide impregnated into a gadolinium-doped ceria (GDC) backbone [2].

Today, these high-temperature electrochemical devices are subject to severe durability constraints. With the current technology, performance degrades by about 2 to 3% after 1000 hours of operation, increasing the energy consumption of the process [3]. To maintain high hydrogen production efficiency, the degradation rate must be limited to a few tenths of a percent (0.5%/1000 h) [4]. Today, the main performance losses are attributed to the degradation of the two electrodes [5]. However, a better understanding of the degradation mechanisms is still needed to improve the electrode stability. This requires detailed characterizations of changes in the microstructure and chemical composition of the electrode components. However, the degradation mechanisms involve complex and interrelated phenomena occurring at the atomic scale. It is therefore necessary to carry out physicochemical and microstructural characterization at this scale.

Objectives and work plan:

In this context, it is proposed to use transmission electron microscopy (TEM) and atomic probe tomography (APT), which are two complementary techniques allowing advanced material characterizations at the atomic scale. A preliminary study has shown that these two techniques can provide very insightful information on the microstructure and stability of the electrodes [6] (Figure 1).

The PhD student will use the various advanced electron microscopy techniques available at the CEA-Grenoble Nano-characterization platform (PFNC) which is equipped with several advanced TEMs. In particular, the student will perform energy dispersive spectroscopy (EDS) and electron energy loss spectroscopy (EELS) analyses at the atomic scale using the latest microscope acquired by the PFNC. The EELS spectra recorded on the new direct detection camera will provide information on the oxidation states of the various elements in the electrode that play a key role in electrochemical reactions.

In addition, complementary characterizations carried out on the new CNRS/SIMAP APT will provide three-dimensional information, which are particularly useful for studying the complex nanostructure of the electrode materials. The correlation of these two techniques will make it possible to obtain quantitative information while avoiding the artefacts inherent in each technique.

The results of these characterizations will be discussed and analyzed using models already available at CEA/Liten. This work should lead to a better understanding of the degradation mechanisms of high temperature electrolysis cells. 

[1] J. Laurencin and J. Mougin in High temperature steam electrolysis: Fundamentals of Solid-State Electrochemistry in SOEC, In ‘Hydrogen Production by electrolysis’, Edited by Agatha Godula-Jopek, Wiley (2015)

[2] C. Nicollet, A. Flura, V. Vibhu, A. Rougier, J.-M. Bassat, J.-C. Grenier, “An innovative efficient oxygen electrode for SOFC: Pr6O11 infiltrated into Gd-doped ceria backbone”, Int. J. Hydrogen Energy, 41 (2016) 15538

[3] J. Mougin, Hydrogen production by high temperature steam electrolysis, Chap. 8 in Compendium of Hydrogen Energy, Vol. 1 : Hydrogen production and purification, V. Subramani, A. Basile, T.N. Veziroglu (eds), Woodhead Publishing Series in Energy, Elsevier, 2015.

[4] Strategic Research and Innovation Agenda, Hydrogen Europe, Oct. 2020

[5] S.J. McPhail,S. Frangini, J. Laurencin, E. Effori, A. Abaza, A. K. Padinjarethil, A. Hagen, A. Léon, A. Brisse, D. Vladikova, B. Burdin, F. Rita Bianchi, B. Bosio, P. Piccardo, R. Spotorno, H. Uchida, P. Polverino, E. A. Adinolfi, F. Postiglione, J.-H. Lee, H. Moussaoui, J.Van herle, Addressing planar solid oxide cell degradation mechanisms: A critical review of selected components, Electrochemical Science Advances 2 (2022)  e2100024

[6] G. Sassone, O. Celikbilek, M. Hubert, K. Develos-Bagarinao, T. David, L. Guetaz, I. Martin, J. Villanova, A. Benayad, L. Rorato, Julien Vulliet, Bertrand Morel, A. Leon, J. Laurencin, Effect of the operating temperature on the degradation of solid oxide electrolysis cells, J. Power Sources, 605 (2024) 234541

The work will be carried out at CEA/Liten, which is a leading research center on new energies, and CNRS/SIMAP, a leading laboratory of Grenoble University in science and engineering of materials.

The candidate must have a master in solid-state physics or material engineering and a strong interest in material characterization.