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As it plays a key role on the performances and durability of solid oxide cells, the electrode microstructure has to be finely characterized and modelled. In this frame, a plurigaussian random field model and an original sphere packing algorithm have been developed to simulate a large variety of electrode microstructures. The two stochastic geometrical models have been validated on various electrode reconstructions obtained by synchrotron X-ray holotomography including the microstructures of thin functional layers and a thick current collector. Afterwards, semi-analytical microstructural correlations have been proposed and validated on a large dataset of representative synthetic microstructures. These equations allow establishing the links between the microstructural properties controlling the performances (Triple Phase Boundary lengths density and specific surface areas) to the 'basic' geometric attributes of the electrode (composition, porosity and particle size distribution). These correlations have been used to model the loss of active TPBl due to the Ni agglomeration.

Microstructural evolution of a Solid Oxide Electrolyser Cell (SOEC) La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) anode is investigated using 3D reconstruction techniques both on a reference and a long-term tested cell. In this framework, reconstructions have been obtained from focused ion beam-scanning electron microscopy and synchrotron X-ray nano-tomography techniques. Microstructural properties extracted from the 3D reconstructions exhibit a slight evolution during the test. Synchrotron X-ray Absorption Spectroscopy (XAS) was also performed, and a modification of the cobalt oxidation state is found. LSCF conductivity decrease due to the change in Co mixed valence has been discussed. Evolutions of both morphological parameters and electrical conductivity were introduced in an in-house micro model to evaluate their impacts on the electrode degradation.

A methodology has been proposed to analyze the electrochemical degradation of the ASC configuration. This methodology, based on the measurement of the cell response by impedance spectroscopy, has been applied to study the cell performances degradation, (i) when the anode is re-oxidized under an ionic current, and (ii) upon direct methane reforming. In the first case, a thin cermet layer growing from the anode/electrolyte interface has been oxidized and then reduced. This 'redox' cycle has been repeated until the complete degradation of the cell. It has been found that the impedance diagram's evolution is consistent with a delamination between the ACC/AFL interface. In the second case, the cell has been operated under methane conditions known to favour the coking. The analysis of the impedance diagrams has shown a degradation of the current collection. This result has been found to be consistent with the location of carbon deposit inside the cell.

The purpose of this work has been focused on the calculation of the stress field inside planar anode supported cells. The cell fracture has been estimated through the statistical approach of Weibull. After elaboration, a high residual compressive stress has been calculated in the thin electrolyte layer. A slight tensile stress has been pointed out in the anode in a region close the anode/electrolyte interface. For high electrolyte thickness (>20 um), this tension leads to low survival probabilities of the anode. At SOFC operating temperature, the elaboration stress is partially relaxed. In this condition, the thermal cycling between the room temperature to the SOFC operating one should not induced any cell degradation. The first cermet re-oxidation step has been also analyzed. This study has shown that the cathode is damaged as soon as the anodic expansion reaches values between 0.05-0.09 %. The electrolyte fracture has been predicted to occur for anodic expansion ranging between 0.12-0.15 %.