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Microstructural evolution in the electrodes plays an important role in the durability of Solid Oxide Cells (SOCs). The metallic phase in the fuel electrodes made of Nickel and Yttria-Stabilized Zirconia (Ni-YSZ) is not stable in operation as it has a high mobility and a rather low wettability to YSZ. To enable long term durability prediction and improve the anode performance, it is necessary to understand its microstructural evolution under different operating conditions. This contribution presents a 3-D geometrical model based on morphological operations. 3-D microstructures of as reduced and aged electrodes were reconstructed by X-ray nanotomography and used to assess the relevance of the model verification. The low computational time of the morphological model allows generating a large database of numerical microstructures for the study of the impact of Ni evolution on the microstructural properties.

A model based on the Phase Field approach has been developed to simulate the local fracture in porous electrode microstructures. The model capacity to predict the crack nucleation and propagation has been studied with theoretical considerations. For the model validation, micro-compression tests have been performed on porous YSZ micro-pillars. As expected, the compressive fracture strength has been found to decrease with the material porosity. Moreover, a transition in fracture mode has been detected from a brittle behavior toward a local damage when increasing the porosity. It has been shown that the model is able to reproduce correctly the experimental results. The validated model has been used to simulate the fracture of the YSZ backbone induced by the Ni re-oxidation in a typical Ni-YSZ cermet. The generation and localization of the micro-cracks have been discussed according to the degree of Ni re-oxidation and the local morphology of the electrode microstructure.

A dynamic physically based model has been developed to unravel the relationships between the overall Solid Oxide Cells response and the reaction mechanisms taking place in the electrodes. This tool combines modules at three different length-scales: electrode microstructures, active functional layers, and single repeat unit. It allows computing the cell polarization together with the distribution of the local current densities, overpotentials, and gas composition. It has been shown that the synthetic electrode model reproduces accurately the real microstructure, which has been checked by comparison with 3D reconstructions. The microscale electrode models have been validated using polarization curves and impedance spectra measured in symmetrical cells. Finally, tests were conducted at different temperatures and inlet flow rates to validate the integrated multiscale approach. For this purpose, a special setup was developed to measure the local current densities in standard cells. A good agreement was found between the experimental and simulated data.

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.

Solid oxide cells with classical Ni-YSZ hydrogen electrodes were operated in fuel cell and electrolysis mode in order to assess the impact of the initial microstructure on the electrochemical and microstructural stability of the cermet. The pristine and aged electrodes have been reconstructed by synchrotron X-ray holotomography. The gradients in microstructural properties have been determined in the vicinity of the electrode/electrolyte interface and in the bulk of the electrodes. Significant Ni depletion was detected only in the electrochemically active region of the aged cells operated in electrolysis mode, while the volatilization is rather limited for the other samples. Besides, substantial Ni agglomeration was confirmed for all aged cermets. The electrode stability was found to depend on the initial electrode microstructure. The microstructural properties have been introduced in multi-scale models to estimate the impact of Ni evolution on the cell performance and to analyze the underlying causes of volatilization and agglomeration.

Solid oxide cells (SOCs) have attracted a growing attention thanks to their high efficiency and ability to operate in both electrolysis (SOEC) and fuel cell (SOFC) modes. Despite its great potential, the current SOC technology faces significant cell degradation during long-term operation. The degradation phenomena are still not well understood as they involve complex and intricate processes arising at different length scales. Additionally, it has been shown that the degradation rate under SOEC operation is generally higher than in SOFC mode. To address this issue, durability tests were performed in SOEC mode at 750, 800 and 850 °C for 2000 h at -1 A cm-2in 10/90 vol.% H2/H2O and dry air. The electrochemical performance of the cells was assessed using electrochemical impedance spectroscopy. In addition, advanced characterization techniques with nanometer and atomic resolution have been used to study material degradation after long-term testing.

Solid oxide cells (SOCs) are high temperature energy-conversion devices, which have attracted a growing interest in the recent years. Indeed, this technology presents a high efficiency and a good reversibility in fuel cell (SOFC) and electrolysis (SOEC) modes. Nevertheless, SOCs durability is still insufficient due to performance degradation during operation. In this context, a physics-based model has been proposed to investigate the impact of operating conditions on the electrodes reaction mechanisms and cell performance. This multiscale model has been developed considering a typical cell composed of a dense electrolyte in Y0.16Zr0.84O1.92(8YSZ) sandwiched between an oxygen electrode in La0.6Sr0.4Co0.2Fe0.8O3-δ-Ce0.8Gd0.2O2-δ(LSCF-GDC) and a hydrogen electrode made of Ni-YSZ. The model has been validated on global and local polarizations curves in SOFC and SOEC modes, and electrochemical impedance spectra at the open circuit voltage (OCV). The different contributions arising in the impedance spectra have been identified and discussed.

Solid oxide electrolysis cells (SOEC) are a promising energy conversion technology for the production of green hydrogen via steam electrolysis. However, performance loss remains a bottleneck for large-scale commercialization. Here, we investigate the different types of degradation occurring in a state-of-the-art cell composed of La0.6Sr0.4Co0.2Fe0.8O3-Ce0.8Gd0.2O2 (LSCF-GDC) composite for the oxygen electrode, GDC for the barrier layer, Y0.16Zr0.84O1.92 (8YSZ) for the electrolyte and Ni-YSZ for the fuel electrode. Electrochemical impedance spectra measured before and after operation at 750 °C for 2000 hours at -1 A cm-2 in SOEC mode revealed no significant evolution for the oxygen electrode contribution. To investigate potential degradation of this electrode, we performed multi-modal chemical imaging based on synchrotron X-ray diffraction (µ-XRD) with a resolution at the micrometer-scale. In addition, we monitored the evolution of the chemical composition and chemical environment before and after ageing using laboratory X-ray photoelectron spectroscopy (XPS). All these analyses revealed a slight evolution of the crystal lattice parameter in the oxygen electrode and the inter-diffusion layer. It was also found that Sr segregation accelerates with ageing. However, more severe ageing conditions and/or longer ageing durations are required in order to observe an effect on the performance.

A set of long-term tests have been carried out in fuel cell and electrolysis modes on typical Ni-YSZ//YSZ//LSCF-CGO cells. In similar operating conditions, the degradation rates were found to be higher in electrolysis than in fuel cell operation. To explain such results, both Ni agglomeration and LSCF destabilization have been investigated by coupling advanced post-test characterizations and modelling. Thanks to 3D electrode reconstructions, it has been found that Ni coarsening upon operation is not sensitive to the polarization, even if the agglomeration explains a significant part of the cell degradation. At the contrary, post-test analyses have revealed that Sr diffusion and formation of SrZrO3 at YSZ/CGO interface occur mainly during electrolysis operation, whereas the process is very limited in fuel cell mode. Therefore, the higher degradation rates measured in electrolysis mode could be related to the higher rate of LSCF demixing.

A long-term test of 2000 h has been carried out on a typical solid oxide cell in electrolysis mode at −1 A.cm−2and 750 °C. The 3D reconstructions of the pristine and aged cermet have revealed a strong Ni depletion at the electrolyte interface. To explain this result, an electrochemical and phase-field model has been developed to simulate the Ni migration in Ni/YSZ electrode. For this purpose, a mechanism has been proposed that takes into account the impact of polarization on the Ni/YSZ wettability. In this approach, it assumes that the Ni/YSZ interfacial energy is changed by the concentration of oxygen vacancies in the electrochemical double layer. Thanks to the model, the Ni migration has been computed in the same condition than the experiment and complemented by a simulation in reverse condition in SOFC mode. In good agreement with the experiment, the simulations have revealed a strong Ni depletion at the electrolyte interface after operation under electrolysis current. On the contrary, a negligible Ni redistribution with a very slight Ni enrichment has been predicted at the electrolyte interface after SOFC operation. These results tend to prove the relevance of the mechanism.

A 31-year-old female patient with a previous history of Carney complex and surgical resection for cardiac myxoma and bilateral adrenalectomy at 18 years old and 10 and 11 years old, respectively, was referred to our department with a diagnosis of recurrent biatrial myxomas incidentally discovered on echography. A magnetic resonance imaging (MRI) confirmed the diagnosis of a tumor protruding into the left ventricle, and the patient underwent a surgical resection of a large left atrial mass and a right-sided atrial small tumor. Diagnosis of bilateral atrial myxomas was confirmed by histologic studies. Postoperative outcome was uneventful, and the patient was discharged at the 7th postoperative day. Few months later, she reported trivial clinical symptoms suspecting a cervical radiculopathy. MRI confirmed the presence of a compressive cervical spinal cord tumoral mass at the C2-3 level leading to perform a surgical exeresis of the tumor. Histology showed a spinal melanotic schwannoma. This case highlights the risk of unexpected ubiquitary tumor locations and the importance of a rigorous transversal multidisciplinary follow-up to prevent severe complications in patients with Carney complex.

A model describing the operation of a Mixed Ionic Electronic conductor (MIEC) has been developed. The main mechanisms and transport phenomena are taken into account. Thanks to a 3D reconstruction obtained by nano-holotomography on a sample prepared with a Plasma Focused Ion Beam (PFIB), the real electrode microstructure has been used into the model. The role of electrode microstructural properties on performances has been estimated through a sensitivity analysis. As the reactive pathways are different in both polarizations, the impact of morphological properties is not the same according to the operating mode. The electrode specific surface area has an effect on the performances and the ratio of the volume fraction to the tortuosity factor of the solid phase has an impact on the electrode response only in cathodic polarization.

A calendar of September 2007 jazz performances in Paris, France, is presented, including Lisa Kirchner, Pat Marino, and Patrick Saussois.