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Solid Oxide Fuel Cells (SOFCs) are a promising technology that can provide efficient and clean energy production. The general barriers hindering their market entry are durability, i.e. resistance to aging, and costs. In parallel to the deeper insight into the different degradation sources and improved understanding of ageing factors and their interactions, work towards higher accuracy for the assessment and monitoring of real-world fuel cell ageing in necessary. The requirements for operational stability formulate the parameter “degradation rate” (DR). Most often long term durability tests are performed at constant current load and the decrease of the voltage is used for its definition. In this work a new approach based on analysis of the volt-ampere characteristics, named Differential Resistance Analysis (DRA), is presented. It operates with the differential resistance, i.e. with the derivative of the voltage in respect to the current (dU/dI = Rd) which is more sensitive to small deviations and thus increases the sensitivity of the analysis. Two performance indicators are derived (Rd, min and ∆U*) with differing selectivity: ∆U* is more sensitive to activation losses and Rd, min - to transport hindrances. The application of the DRA is demonstrated on examples from measurements in fuel cell and in reverse (fuel cell/electrolyzer) mode, as well as on modeling data. The results show that the method is at least 10 times more sensitive to DR evaluation in comparison with the classical approach.

International audience; The present work proposes to explore how the presence of a periodic pattern at electrode/electrolyte interfaces of a SOFC could impact the electrochemical performances, from theoretical and experimental points of view. The model results demonstrate that a patterned interfaces along with an electrolyte having a thickness smaller than the dimensions of the pattern, lead to a strong increase of the exchange surface, hence to the exchange currents (up to 64%) with respect to flat interfaces. With the use of laboratory standard ceramic processes, this architecturation was experimented on YSZ-Ni self supported anodes on top of which a thin YSZ electrolyte was deposited. The first electrical tests for such a cell with a non-optimized thickness show an increase of the current density with respect to a cell with flat interfaces, from 130 to 300 mA cm-2 at 0.7 V, that is even higher than anticipated by the modeling.

International audience; Nowadays, the valorization of biomass, biowastes and by-products is among the key issue to be considered in the development of renewable energies from bioresources. Accurate analysis and characterization of these feedstocks is a crucial aspect in the understanding of their behaviour for further use. This chapter is focused on different characterization techniques which are commonly used up-to-date. They are classified in different categories: Sampling and storage; Proximate analysis; Ultimate analysis; Thermal analysis, Physical characterizations; Physico-chemical characterizations; Structural and textural characterizations; and Mechanical characterizations. For each of them, a general description of the technique is presented, followed by useful information on machines and experimental conditions such as sample preparation, sample pre-treatment, gas atmosphere, temperature program etc. Finally, examples, results treatment and exploitations will be provided to illustrate. This chapter provides an insight on generic and advanced characterization techniques for complex materials, such as biomass, biowastes and related bio-products, that will be again discussed along the handbook in the other chapters.

International audience; Solid co-products from biochemical, chemical and thermochemical processes of biomass and biowaste have gained momentum in utilization as secondary raw materials. These solids are carbon-based or mineral-based materials, and for their suitable use in a number of fields, various properties should be determined. This chapter addresses advanced techniques used to determine physical and chemical properties of these solid residues. For each technique, the basics and protocols are described. Post-treatment procedures and interpretation of the results obtained are also provided for some residues.

International audience; The catalytic activity of pyrolysis chars from bio-waste was investigated for the cracking of model tar compounds (ethylbenzene and benzene). Two pyrolysis chars were produced at 700 °C from (1) used wood pallets (UWP), and (2) a 50/50 dry% mixture of food waste (FW) and coagulation-flocculation sludge (CFS). Steam activation at 850 °C was used to study the influence of the porous structure. While coke deposition is known to be responsible for the deactivation of carbonaceous chars and metal catalysts during tar cracking reactions, the deactivation of complex materials such as bio-waste chars has scarcely been studied. For this reason, special attention was paid on the relationships between the physicochemical properties of the chars, the operating conditions, and the deactivation mechanisms. To this aim, the cracking tests were performed over a wide temperature range: 400–650 °C for the ethylbenzene cracking, and 850–950 °C for benzene cracking. After the ethylbenzene cracking tests at 650 °C, the characterisations performed with SEM, BET, FTIR and Raman revealed that coke deposition was responsible for the char’s deactivation. The high specific surface area of activated chars explained their higher catalytic activity, and mesoporous catalysts were proved to be more resistant to coke deactivation than microporous catalysts. For these reasons, the higher ethylbenzene conversion (85.8%) was reached with the activated char from food waste and sludge (ac.FW/CFS). For benzene cracking at higher temperature (850 and 950 °C), the chars from food waste and sludge (FW/CFS) were the most active catalysts, despite their deactivation by the melting, diffusion and sintering of the inorganic species. This original deactivation mechanism, reported for the first time, led to the formation of an inorganic layer composed of P and Ca species at the char surface, with some areas rich in KCl and NaCl. Non-activated char from food waste and sludge (c.FW/CFS) was surprisingly proved to be more resistant to deactivation by inorganic species than the activated char (ac.FW/CFS) during the benzene cracking tests at 950 °C. This extended catalytic activity was explained by the activation of the non-activated char (c.FW/CFS) with the CO2 contained in the syngas which simultaneously developed the porosity and created new available active sites. This study marks a step forward in the understanding of the relationships between the deactivation mechanisms, the physicochemical properties of the chars, and the cracking temperature. Finally, a proposal for process integration is presented to consider the possibility to valorise the chars as catalysts to decompose the tar generated in the same pyro-gasification process.

International audience; This study aims at understanding the structural changes occurring in the carbonaceous matrix of wood-based chars during their thermal conversion. Although chars are routinely characterized by porosity measurements or scanning electron microscopy, the composition and structure of the carbonaceous matrix is often not investigated. Here, advanced characterization using X-ray synchrotron microtomography, transmission electron microscopy, Raman spectroscopy and X-ray diffraction provided a precise description of the char properties, allowing for an accurate discussion of their catalytic properties. Two chars were produced by slow pyrolysis of wood waste (400 and 700 °C) and a third one was fabricated by activation under steam at 850 °C of the char obtained at 700 °C. The results show that the pyrolysis temperature and the activation performed did not affect the macrostructure of the chars and that the pores were interconnected at the macroscopic scale. However, at 700 °C, the micro- and nanostructures were modified: short-range organized graphene fringes were observed. The activated char showed a homogeneous microstructure similar to that of its precursor. Besides, the ratio of graphene-like structures, the local organization of graphene sheets, and the imperfections in graphene-like sheets were clearly improved by the post-treatment. To our knowledge, this is the first time that such an approach, combining various tools, is applied for the study of pyrolysis chars.

International audience; Syngas from thermochemical conversion of waste or biomass is a renewable energy carrier that may contain pollutants – such as tar – that should be removed before further syngas utilisation. Chars have proved to be promising catalysts for tar cracking, but the influence of the physico-chemical properties on their reactivity is still unclear. This work aimed to better understand the structure and the composition of the mineral species of pyrolysis char, as well as their catalytic role in tar cracking. For this purpose, a characterisation of the minerals has been performed at bulk, surface (studied at micro and nano-scale) and crystallite scale. Pyrolysis chars were produced from wastes generated on cruise ships – namely used wood pallets (UWP), food waste (FW) and coagulation flocculation sludge (CFS) – having different mineral amount and content. Ethylbenzene was used as surrogate of light aromatic hydrocarbons in a tar cracking process. The results showed that ethylbenzene was converted into lighter gases meaning that the chars were efficient for this. Ethylbenzene conversion at 650 °C was found to be significantly higher with the char from a mixture of sludge and food waste (c.FW/CFS) compared to that of wood-based char (c.UWP): 71 wt.% against 45 wt.%, respectively. The combination of multi-scale and complementary techniques has highlighted that the higher catalytic activity of this char was mainly attributed to the mineral content. Well dispersed mineral particles with various morphologies and natures were observed on the surface of c.FW/CFS using Scanning and Transmission Electron Microscopy (SEM and TEM). Especially, Ca, Al and P were the main mineral species identified using XRFS and SEM. These mineral species in form of oxides and hydroxyapatite were considered to be the main active mineral components for tar cracking. Oxides were identified using EDX-analysis. XRD analysis highlighted the presence of crystalised particles of hydroxyapatite (Ca5(PO4)3(OH)), while Raman spectroscopy revealed that these particles were embedded in the carbon matrix.

International audience; Novel ionic conductors were prepared by substituting Ca2+ and Sr2+ for Gd3+ in Gd3GaO6. A microwave-assisted combustion technique was used to synthesize these compounds at 900 °C. SEM observations showed that both substituents promote grain growth during sintering. XRD proved that the Gd3-x(Ca,Sr)xGaO6-x/2 solid solutions are formed up to x = 0.10. Below 600 °C, the level of conductivity under wet Ar is higher than that of measured under dry atmospheres, thereby demonstrating the contribution of proton defects to the overall conductivity. The highest level of proton conduction, i.e. σ600°C = 1 × 10−3 S cm−1, was measured for Gd2.9Sr0.1GaO5.95 at 600 °C in wet Ar. At higher temperatures, only oxygen ions contribute to the conductivity. At 800 °C, a total oxide-ion conductivity of σ800°C = 1 × 10−2 S cm−1 was measured for the highest substitution level, i.e. x = 0.10. In both temperature ranges, activation energy associated with ionic transport decreases with the Me content as a result of an increase in grain size. Stability tests were successfully achieved as the structure of materials remains unchanged after different treatment under severe conditions. Conductivity measurements under varying oxygen partial pressures demonstrated that materials are purely oxide-ion conductors up to pO2 = 1 × 10−5 atm. At higher pO2, a p-type contribution appears.

International audience; This paper reports impedance studies of a dual membrane fuel cell - an innovative design based on the idea for a junction between an oxygen ion conducting cathode/electrolyte part and proton conducting anode/electrolyte part through a mixed oxygen ion and proton conducting porous membrane. Thus oxygen, hydrogen and water are located in three independent chambers. This concept allows avoiding all the severe pitfalls connected to the presence of water at electrodes in both SOFC and PCFC. The performed measurements of the 3 compartments and the data analysis are improved by introducing some specialized approaches and techniques, which are discussed. The impedance contribution in the proof of the new concept is also presented.

The acceptor-substituted BaSn0.875M0.125O3-δ (M = Sc, In, Y, and Gd) proton conductors were prepared by a wet chemical method. The effects of dopant nature on the structure, hydration energy and proton conduction have been investigated. Analysis of XRD data showed that all compounds present a cubic perovskite structure (space group: P m 3 − m ). Thermogravimetry analysis showed that the significant mass of water was gained in wet Ar during measurements, and the most negative hydration energy is observed for Sc-substituted BaSnO3 (−86 kJ/mol). However, Y-substituted BaSnO3 exhibits the highest proton conductivity at low temperature under wet Ar, such as the total conductivity is 4.8 × 10−4 S/cm at 600 °C.

Des materiaux tels que les apatites a base d'oxydes de lanthane et de silicium ou des perovskites conductrices protoniques, potentiellement utilisables au sein de piles a combustible, presentent une grande resistance au frittage. Celle-ci limite d'autant plus leur utilisation au sein de piles a combustible, surtout s'ils doivent etre employes comme electrolytes. Plusieurs strategies peuvent etre envisagees pour remedier a ce probleme parmi lesquelles l'emploi de nouvelles methodes de frittage ou le choix d'une methode de synthese efficace (permettant par exemple de diminuer la taille des grains ou de limiter celle des agregats souvent redhibitoires au moment du frittage). Nous presentons ici les resultats de frittage par Spark Plasma Sintering (appele par la suite SPS) en les comparants a ceux obtenus par frittage conventionnel haute temperature. Les materiaux etudies ont des compositions derivees des phases La 9,33 □ 0,67 Si 6 O 26 et BaZr 0,9 Y 0,1 O 2,95 □0,05 pour lesquelles des problemes de frittage ont ete rencontres. Nous insisterons sur les particularites des materiaux obtenus par SPS en termes de structure et microstructure et des consequences sur les proprietes de transport anionique.

International audience; Images of a hematite-based epoxy coating are obtained by scanning electron microscopy (SEM). At the scale of a few micrometers, they show aggregates of hematite nano-particles organized along thin curved channels. We first segment the images and analyze them using mathematical morphology. The heterogeneous dispersion of particles is quantified using the correlation function and the granulometry of the embedding (epoxy) phase. Second, a two-scales, 3D random microstructure model with exclusion zones is proposed to simulate the spatial distribution of particles. This simple model is parametrized by four geometrical parameters related to the exclusion zones solely. The microstructure is numerically optimized, in the space of morphological parameters, on the granulometry of the embedding epoxy phase and on the microstructure correlation function, by standard gradient-descent methods. Excellent agreement is found between the SEM images and our optimized model. Finally, the size of the representative volume element associated to the optimized microstructure model is compared with that of the SEM images.

In the high current density regime, the performance of SOFCs is limited by concentration overpotentials, which are particularly significant at the anode side where a competition occurs between incoming hydrogen and outgoing water. In standard SOFCs where the anode is made of YSZ and Ni, this becomes crucial when the demand for reactants exceeds the capacity of the porous cermet anode to supply them by gas diffusion mechanisms. A delicate compromise should be found between maintaining a high level of activation in the anode, i.e. high density of triple phase boundaries (TPB), favored by a distribution of small interconnected pores with high tortuosity and small grains size, and high gas permeability, favored by a distribution of large interconnected pores with low tortuosity, while the percolation of both electronic and anionic conductivity phases is maintained. The present work aims at determining experimentally anodes gas permeability as a function of the experimentally determined percolation, tortuosity and volume fraction of the pores, assuming that the diffusion of gases is described by the Darcy Law. Anodes with varying porosity ensured by different quantities of the pore former were obtained by cold pressing and sintering. SEM image analysis, mercury intrusion porosimetry and permeability measurements for different gases were performed. The obtained results show that permeability increases with the volume fraction of the pore former. However, non-linearity as a function of the gases molecular weight is observed and discussed as a function of the mean free path and thus of possible mixed Darcy and Knudsen diffusion.

The route for the increase in SOFC performances is many-fold: i/ in the low current density domain, through the enhancement of the catalytic properties of the electrodes, i.e. via a higher Triple Phase Boundary (TPB) density, hence a higher exchange current and a lower activation overpotential, ii/ in the ohmic loss region, through lower resistance, i.e. via thickness reduction, materials with a higher conductivity, iii/ in the high current density region, via the optimization of the electrodes microstructure, i.e. the control of the porosity, of the tortuosity and percolation of phases. Taking ideas from the batteries community, where the conceptual design of electrodes is much more mature, the present work proposes to explore how the corrugation of electrode/electrolyte interfaces impacts the performances. This approach was applied to the anode/electrolyte interface of a SOFC based on standard compositions, YSZ (or YDC) for the electrolyte, and YSZ (or YDC) + nickel for the anode. The corrugation of surfaces was obtained through the patterning of this interface with different geometries (flat, pyramids, shallow and deep ellipsoids) at the 10-100 µm scale by cold pressing, templating or serigraphy. Thin electrolyte layers have been deposited on top of these architectures by Atomic Layer Deposition (ALD). In parallel, an electrochemical model was carried out and implemented by considering masses and charges conservation, gas transport and electrochemical reaction kinetics throughout the interface in FEM (finite element method) with COMSOL Multiphysics. The results showed a 25 % increase in the total current density for a certain ellipsoid geometry.

International audience; The oxide-ion and proton conduction properties of RE3NbO7 (RE = La, Gd, Y, Yb, Lu) compounds were investigated. For the bigger rare-earth cation, i.e. La3+, the compound crystallises in a weberite-type structure and the oxide-ion conductivity is low owing to the lack of intrinsic oxygen vacancies. Consequently, the resultant proton incorporation and conductivity in La3NbO7 are also low. For small rare-earth cations, i.e. from Gd3+ to Lu3+ and for RE = Y, materials adopt a fluorite-like structure confirmed from X-ray powder diffraction. In this latter case, materials include intrinsic oxygen vacancies leading to a higher oxygen conductivity. For these compounds, a proton incorporation takes place at low temperature under wet conditions giving rise to proton conductivity. Nevertheless, both oxygen and proton conductivities are low in these materials, which can be explained by the ordering of oxygen vacancies observed by Transmission Electron Microscopy.

International audience; In-substituted BaSnO 3 (BaSn 1Àx In x O 3Àδ , x ¼ 0:125, 0.25 and 0.50) compounds were prepared by a gel polymerization method. Their microstructure, hydration energy and electrical properties were investigated. Single phases were confirmed by X-ray dif-fraction analysis over the whole range of substitution, and were identified as cubic perovskite-like structure. The grain size and conductivities of samples measured under dry and wet atmospheres increase significantly with indium content as such, 1À2 μm for BaSn 0:875 In 0:125 O 3Àδ (x ¼ 0:125) and 20 μm for BaSn 0:50 In 0:50 O 3Àδ (x ¼ 0.50). The highest proton conductivity at 600 ○ C, ¼ 9:5 Â 10 À4 SÁcm À1 , is obtained for BaSn 0:5 In 0:5 O 2:75 (x ¼ 0:50). Barium stannates with chemical formula derived from BaSnO 3 has recently been proposed as protonic conductors with potential applications in fuel cells. 1À6 It was shown that Y-substituted BaSnO 3 materials exhibit high proton conductivity in wet atmospheres. 5,6 Nevertheless, barium stannate based compounds exhibit a strong aversion against densification, i.e. the relative density reaches only about 90% with difficulty although sintered at 1600 ○ C for 12 h. 5,6 Such a high sintering temperature possibly results in barium volatilization leading to the decrease of proton conductivity, and also makes this oxide difficult to integrate electrochemical devices. 7,8 In the literature, the In element has received much less attention than the rare earth elements as a substituant for proton-conducting perovskites. 9À21 Matsumoto et al. 22 reported that electrical performances of BaCe 0:90 In 0:10 O 3Àδ are much more lower than those of the counterparts substituted with other trivalent dopants (Y, Tm, Yb and Sc). Zhang et al. 20 pointed out that the proton concentration and electrical properties of BaCe 0:80Àx Sm 0:20 In x O 3Àδ decrease when the indium content increases. However, Giannici et al. 21 reported that a high content of vacancies can be created by the substitution of Sn 4þ for In 3þ in BaSnO 3. Shober et al. 2 also point out that BaSn 0:5 In 0:5 O 2:75 (x ¼ 0:50) go along with high proton defects, then exhibits a high level of grain conductivity, nevertheless it is relatively unstable in severe reducing atmospheres. The literature showed that in substitution in BaCeO 3 plays a beneficial role on the stability and sinterability of proton-conducting perovskites in CO 2 atmosphere. 9,20 Moreover, indium as a second substituent improve the sinterability of BaZr 0:9 Y 0:1 O 3Àδ while yttrium enhance the proton conductivity. 18 In this paper, the effect of the substitution of Sn 4þ for In 3þ in BaSnO 3 on the micro-structure, water hydration and electrical properties has been investigated. BaSn 1Àx In x O 3Àδ (denoted x ¼ 0:125, 0.25 and 0.50 as BSIn125, BSIn25 and BSIn50 in the following) powders have been synthesized by a gel polymerization route from an aqueous solution containing cation salts. 5,6,23 The resultant precursors were heat-treated at 1200 ○ C for 4 h to obtain §

In this study, the synthesis, structural and electrical properties of BaSn 0.75 M 0.25 O 3− δ (M = Fe, Sc, In, Y, Gd, Sm, Nd and La) compounds have been investigated. Single phase powders of these materials were successfully synthesized by a gel polymerization route and sintered to obtain dense pellets. X-ray diffraction reveals that all compounds crystallise in a cubic perovskite like-structure (space group: Pm 3 ¯ m ) at room temperature. However, cell parameters of the substituted compounds do not evolve in accordance with the substituent radius, i.e. an abnormal drop was observed for elements with a large radius, i.e. Sm, Nd and La. A possible interpretation could be the partial incorporation of substituents into the Ba-site. The site incorporation selectivity of substituents into the Ba- and Sn-sites was investigated based on the study of lattice parameters and empirical defect models. Experiments show that the thermal expansion coefficients and electrical properties have no specific correlation with the nature of the substituent.

International audience; The effects of ZnO additive on the phase formation, microstructure and electrical conduction of Y-doped BaSnO3 have been investigated. The single-phase and dense BaSn0.75Y0.25O3−δ compound with 4 mol% ZnO additive was successfully prepared after sintering at 1300 °C, which significantly reduces the sintering temperature. The conductivities measured under dry and wet air atmospheres reveal that the bulk conductivity of BaSn0.71Y0.25Zn0.04O3−δ is much lower than that of BaSn0.75Y0.25O3−δ. However, ZnO as a sintering aid does not affect the bulk conductivity. The total conductivity of BaSn0.75Y0.25O3−δ with ZnO as the sintering aid is slightly higher than that of unmodified BaSn0.75Y0.25O3−δ, and reaches 2.4 × 10−3 S cm−1 at 621 °C. Therefore, this material can be used as a proton-conducting electrolyte for intermediate temperature solid oxide fuel cells.

International audience; Ba2SnYO5.5 nanopowders were synthesized by a gel polymerization method. In this process, a gel containing Ba, Sn and Y cations has been obtained by the polymerization of acrylic acid using N,N′-methylene bis-acrylamide as a cross-linking reagent and hydrogen peroxide as an igniting reagent. The gel was calcined at 1200 °C, giving rise to the Ba2SnYO5.5 single-phase nanopowders with the grain size ranging from 50 nm to 70 nm. Nanopowders were sintered at 1150 °C by spark plasma sintering (SPS) to obtain dense nanostructure materials (> 95%) containing grains whose size ranges between 70 nm and 100 nm. Nanostructured Ba2SnYO5.5 shows a good chemical stability in wet atmosphere. However, its protonic conductivity decreases compared with that of microcrystallin Ba2SnYO5.5 ceramics.

IDEAL-Cell is a new concept of a high temperature fuel cell operating in the range 600-700 °C. It is based on the junction between the anode part of a PCFC and the cathode part of a SOFC through a mixed H+ and O2- conducting porous ceramic membrane. This concept, extensively described in the present paper, aims at avoiding all the severe pitfalls connected with the presence of water at the electrodes in both SOFC and PCFC concepts. Spark Plasma Sintering samples were designed specifically for proving the IDEAL-Cell concept. The first electrochemical results obtained at 600 °C under hydrogen on millimeter thick samples show that IDEAL-Cell behaves like a high temperature fuel cell. It is estimated that the overall efficiency of this new concept should greatly surpass that of standard SOFCs and PCFCs and that the material constraints, especially in the case of interconnect materials, should significantly decrease.

International audience; Atomistic simulations have been used to investigate energetic aspects of defects in pure and doped BaSnO3, in close comparison with experimental data. Semiempirical potentials were used to determine the solution energies of trivalent cation on either A or B site of the perovskite structure. Density functional theory calculations were also performed to gain further insight into the redox properties of this material. Both approaches give a complete view of the way doping atoms will be inserted inside the BaSnO3 structure. For instance, we calculated with good precision the evolution of cell parameters with dopant nature and concentration. Then, by taking into account dopant vacancy interactions, we also show that the oxygen vacancy preferentially locates close to the dopant in the case of small size dopant while stays at the second neighbor position in the case of bigger dopant. These calculations also show that In and Y are the dopants giving the most homogeneous energetic map for oxygen vacancy movements and might thus be anticipated as the best acceptor-like dopants for enhanced anion conduction properties. Finally, we calculated an oxygen ion migration activation energy of 0.65 eV.

International audience; This work explores experimental procedures for tape-cast proton conducting ceramic fuel cells (PCFC) based on Yttrium-doped Barium Cerate (BCY10). The work is based on several years experience on aqueous tape-casting applied to the shaping of YSZ-based SOFC: however, water-based tape casting of BCY10 appeared to be impracticable for reasons associated with the high basicity of this material that results in rapid hydrolysis when in contact with water. Organic tape casting was therefore developed for BCY10, but only on Electrolyte (BCY10)/Anode (BCY10 + NiO) half cells since up to now no cathode material is available. Planar 20 mm diameter circular half-cells were obtained with the aid of a small load on top of the bi-layer to counterbalance the inevitable warping of the samples. Back-scattered SEM and X-Ray computer-controlled microtomography showed sedimentation of some large grains in the green tapes which are believed to have formed by a mechanism associated with a porosity gradient. The deformation occurring during sintering was modelled taking into account the elastic, thermal, viscoplastic and sintering components of the total deformation. 2D and 3D Finite Element numerical simulations showed that the driving force for deformation is associated with this porosity gradient.

Oxy-apatite materials La 9.33 + x Si 6 O 26 + 3 x /2 are thought as zirconia-substitutes in Solid Oxide Fuel Cells due to their fast ionic conduction. However, the well-known difficulties related to their densification prevent them from being used as such. This paper presents strategies to obtain oxy-apatite dense materials. First, freeze-drying has been optimized to obtain ultrafine and very homogeneous La 9.33 + x Si 6 O 26 + 3 x /2 (0 ≤ x ≤ 0.67) nanopowders. From these powders, conventional and Spark Plasma Sintering (SPS) have been used leading to very dense samples obtained at temperatures rather lower than those previously reported. For instance, SPS has allowed to prepare fully dense and transparent ceramics from 1200 °C under 100 MPa. The microstructure and transport properties of such samples have been then evaluated as a function of sintering conditions and lanthanum content. It will be show that for lanthanum content higher than 9.60 per unit formula, the parasitic phase La 2 SiO 5 appears leading to a degradation of conduction properties. We also show that grain boundaries and porosity (for conventionally-sintered materials) seem to have blocking effects on oxygen transport. The highest overall conductivity values at 700 °C, i.e. σ 700 °C = 7.33.10 − 3 S cm − 1 , were measured for La 9.33 Si 6 O 26 material conventionally-sintered at 1500 °C which contains bigger grains' size by comparison with σ 700 °C = 4.77.10 − 3 S cm − 1 for SPS-sintered materials at the same temperature but for few minutes. These values are associated with activation energies close to 0.83–0.91 eV, regardless of sintering condition, which are commonly encountered for anionic conductivity into such materials.

An alternative route to acrylamide gel polymerisation is presented for the preparation of oxide nanopowders. Within this method, cations first dissolved in an aqueous solution are subsequently trapped inside a 3D chelating gel beforefast-drying, which leads to a stable precursor. In this study, we have prepared compositions corresponding to a wide range of state-of-the-art fuel cells materials such as: Zr0.85Y0.15O1.875, Ce0.9Gd0.1O1.95, Nd1.95NiO4+x, GdBaCo2O5+x, Ba0.5Sr0.5Co0.8Fe0.2O3–x and La0.75Sr0.25Cr0.5Mn0.5O3. Thermogravimetry and differential thermal analysis studies have been performed to determine the best calcination conditions. After calcination, the resulting powders have been characterised by X-ray diffraction, FEG-scanning electron microscopy and TEM. The synthesised powders are of nanometric crystallite size and have flake-like aggregates; pure phases are obtained at low temperature. We made this method more attractive by using a nontoxic polymer and a nonexplosive initiator. This route allows the easy preparation of more than tens of grams of nanometric powders in one batch. Finally, since this process is largely independent of the formula of the compound, it can easily be extended to other kinds of oxides such as ferroelectric, CMR (colossal magnetoresistance) or gas sensor compounds.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

International audience; The hydration properties of Lanthanum-doped barium stannate have been studied using density functional calculations. The interaction energy between elementary defects (proton-dopant and oxygen vacancy-dopant) have been calculated in charged states corresponding to p-type conditions. Surprisingly, the most attractive energies are not found for first-neighbor relative positions. The geometric distortions and the electronic densities of state in the different configurations involved are presented. With these data, two simple models are used to estimate the energy of the hydration reaction.

Lanthanum silicate oxyapatites, ion-conducting materials presenting a strong aversion against densification, have been obtained in the form of dense transparent ceramics, by combining the beneficial use of freeze-drying and spark plasma sintering methods.

The EVOLVE cell, named after a running FP7 project, is an innovative SOFC concept that integrates advanced materials, providing multiple functionalities (electrochemical activity, ion or/and electron conduction, gas diffusion…), and an inventive anode current collector made of a NiCrAl preoxidized foam impregnated with a conductive perovskite. Therefore, this anode combines the beneficial characteristics of MSC and ASC technologies, and strong improvements in terms of reliability and durability (inter-diffusion, Ni coarsening and agglomeration, sulphur tolerance, mechanical robustness and chemical stability under redox cycling in temperature) are expected. In order to enhance the electrode efficiency, the 3D microstructure needs to be precisely described at the microscopic scale by a morphology model. An optimized microstructure (controlled pores size, morphology and connectivity, grains size distribution, 3D tortuosity and 3D percolation of phases, volume fraction of phases, final thickness of components …) is closely related to the starting parameters (nature and quantity of starting powder, binder, shaping aids…) and to the control of the shaping process parameters (sintering treatment and atmosphere). It should meet the best compromise between a good electrocatalytic activity and a low ohmic resistivity while ensuring a stisfactory long term thermomechanical stability on the life time of the device. Based on a mathematical morphology approach applied on symmetrical LST/CGO anode layers, the present work aims at showing how a morphology model can be establised and 3D microstructural data relevant for shaping and performances can be derived from back-scattered electrons (BSE) SEM observations. For each sample, a series of images were used as input information for the microstructural modelling. All the original images were first filtered to remove the noise, thresholded and finally a series of morphological operators (openings, surface openings, closings and reconstruction with markers) were applied to remove artefacts. A 3D pluri-Gaussian model has been generated from 2D images, and then computed to predict volume fraction of the 3 phases, 3D tortuosity, gas permeation and ionic conductivities. These results were used for the optimization of the shaping process that includes the integration of the metal foam.

7 pages; International audience; New oxygen ion conductors have been prepared by substituting Ga3+ for Ge4+ in Nd4GeO8, Zn2+ and Mg2+ for Ga3+ in Nd3GaO6, and Ca2+ and Sr2+ for Nd3+ in Nd3GaO6. A combustion technique using ethylenediamine tetraacetic acid has been developed to synthesize these materials at ~900 C, leading to powders with spherical particles of about 100-200 nm. The green pellets obtained through the combustion-synthesized powders could be sintered to ~98% at 1250 C. It was found that Nd4Ge1-xGaxO8-x/2 are formed up to x = 0.10, Nd3Ga1-xMxO6-x/2 (M = Zn, Mg) up to x = 0.03, and Nd3(1-x)M'3xGaO6-3x/2 up to x = 0.03 and 0.015 for M' = Ca and Sr, respectively. These relatively small substitution rates induce a significant increase in oxygen ion conductivity (800C = 0.2 × 10-2 S cm-1 for Nd4Ge0.9Ga0.1O7.95; 800C = 0.5 × 10-2 and 0.4 × 10-2 S cm-1 for Nd3Ga0.97M0.03O5.985 with M = Zn and Mg, respectively, and 800C = 0.6 × 10-2 and 0.7 × 10-2 S cm-1 for Nd2.91Ca0.09GaO5.955 and Nd2.955Sr0.045GaO5.9775, respectively) with respect to pure Nd4GeO8 (800C = 2.8 × 10-4 S cm-1) and pure Nd3GaO6 (800C = 2.7 × 10-4 S cm-1).

The structural, dynamical and dielectric properties of the cubic phase of perovskite barium stannate BaSnO3, a potential candidate as protonic conductor for solid oxide fuel cells, have been investigated by the means of first-principles density functional calculations, and the structural and electrical properties have been explored at low temperature. From density functional perturbative calculations, the phonon modes, the Born effective charges and the dielectric tensor are derived and analyzed, at zero pressure. The phonon band-structure of the cubic phase does not exhibit unstable modes, in good agreement with x-ray diffraction, which shows that BaSnO3 remains perfectly cubic down to 10 K. The dielectric response in BaSnO3 as measured and calculated is lower than in titanate and zirconate perovskites.

This work is dedicated to the development of a numerical model to optimize the anodeelectrolyte interface geometry for improving the electrochemical performance of a SOFC cell in a 3- Dimensional SOFC simulation process. A SOFC repeated unit composed of anode, electrolyte and cathode is taken as a modeling target. The model is implemented by considering electron and ions conservation, gas transport and electrochemical reaction kinetics in FEM (finite element method) software COMSOL Multiphysics. Four different interface geometries—flat, pyramid, ellipsoid and cube, which are predicted to show better electrochemical performance due to increased TPBs and less activation resistance, are investigated to find the best morphology according to their simulated performance. Results reveal that the cubic interface case achieves the highest current density at fixed 0.7V cell operating voltage, 63.55% higher than the flat reference interface. Distribution of different electrochemical variables is also obtained in each condition, giving valuable information for further optimization.