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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; 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.

The Ln4[Ga 2(1-x) Ge 2x O 7+x □ 1-x ]O 2 (Ln = La, Nd, Gd; x ≤ 0.4) compounds have been prepared first by solid-state reaction and then by a new regenerative sol-gel method which allows their sintering. They exhibit a Cuspidine-like structure. Upon substituting Ge 4+ for Ga 3+ , the Cuspidine structure is maintained up to x = 0.4. For x ≥ 0.15 a 1D modulation of the structure was observed and analyzed as driven by composition. The Ge 4+ substitution for Ga 3+ with concomitant filling of oxygen vacancies is beneficial to the anionic conductivity which increases rather regularly with x to reach 10 -3 S/cm at 800 °C for x = 0.4 and Ln = Nd. Conductivity measurements on Ln4[Ga 2(1-x) Ge 2x O 7+x □ 1-x ]O 2 (Ln = La, Nd, Gd) compounds with a fixed Ge content (x = 0.2) show a clear increase of the activation energy when the ionic radii of the Ln 3+ cation decreases. La and Nd compounds exhibit similar conductivities, significantly larger than that of the Gd counterpart.

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.

The Nd4[Ga2(1−x)M2xO7+x□1−x]O2 (M=Ti, Ge) compounds have been prepared by solid state reaction. Nd4(Ga2O7□)O2 and Nd4(Ti2O8)O2 both exhibit a cuspidine-like structure and they form a complete solid solution. Upon substituting Ge for Ga, the cuspidine structure is maintained up to x=0.3. Although both Ti and Ge substitutions for Ga induce a concomitant filling of oxygen vacancies, opposite effects are observed on the oxide ion conductivity: Ti plays a detrimental role whereas the Ge improves the conductivity. A possible interpretation is that additional oxygen atoms are trapped in the coordination polyhedron of Ti4+ whereas they are forced to increase the coordination number of Ga3+ when Ge4+ is introduced in the structure. The highest conductivity at 800 °C, σ≈0.5×10−3 S/cm, is obtained for Nd4[Ga1.8Ge0.2O7.1□0.9]O2.

International audience; Recently a new design of solid oxide fuel cell (SOFC) named dual membrane fuel cell (dmFC) has been introduced and proved. It is based on the introduction of three independent compartments for hydrogen, oxygen and water, which eliminate the dilution of the fuel or the oxidizer respectively in the SOFC construction or in its proton conducting (pSOFC) modification. Due to the registered sufficient mixed ionic conductivity of BaCe0.85Y0.15O2.925 (BCY15), a simplified modification in respect to shaping technology and construction is introduced. It's performance is better than the one of pSOFC cell produced with the same material and shaping procedure: 76 mW/cm2 (dmFC thickness 1.1 mm) against 71 mW/cm2 (pSOFC thickness 0.66 mm) at 700 °C. Impedance measurements carried out down to 1 mHz ensure information about the water formation and behaviour in the separate central membrane compartment of the dmFC design, which brings to performance improvements, registered also in electrolyser mode of operation.

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.

This paper presents results for the conductivity of BaCe0.85Y0.15O2-δ (BCY15) measured by electrochemical impedance spectroscopy in wet hydrogen and in Air, as well as test results from the application of the material in a new dual membrane fuel cell configuration (“IDEAL Cell”), in which the water is produced and evacuated through a separate chamber. The conductivity of dense BCY15 in wet hydrogen atmosphere at 700 °C is 2.0 10-2 S/cm. The measured values in air are of the same order. Preliminary tests of the material in the new cell design, where the three types of conductivity (protonic, oxide ion and mixed) are used in different cell compartments, are successfully performed.

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.

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).