Anode supported single chamber solid oxide fuel cells operating in exhaust gases of thermal engine

International audienceThis project deals with the development and the electrochemical characterization of anode supported single chamber SOFC in a simulated environment of thermal engine exhaust gas. In the present work, a gas mixture representative of exhaust conditions is selected. It is composed of hydrocarbons (HC: propane and propene), oxygen, carbon monoxide, carbon dioxide, hydrogen and water. Only oxygen content is varied leading to different gas mixtures characterized by three ratios R = HC/O2. Concerning the cell components, a cermet made of nickel and an electrolyte material, Ce0.9Gd0.1O1.95 (CGO) is used as anode and two cathode materials, La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF) and Pr2NiO4+δ (PNO), are evaluated. The prepared cells are investigated in the various gas mixtures for temperatures ranging from 450 °C to 600 °C. Ni-CGO/CGO/LSCF-CGO cell has delivered a maximum power density of 15 mW cm−2 at 500 °C with R = HC/O2 = 0.21, while lower power densities are obtained for the other ratios, R = 0.44 and R = 0.67. Afterwards, LSCF and PNO cathode materials are compared and LSCF is found to deliver the highest power densities. Finally, by improving the electrolyte microstructure, some cells presenting a maximum power density of 25 mW cm−2 at 550 °C are produced. Moreover, up to 17% of initial HC are eliminated in the gas mixture

Neodymium electrowinning into copper-neodymium alloys by mixed oxide reduction in molten fluoride media

The possibility of neodymium electrowinning from neodymium oxide using a reducing agent (RA) produced in-situ by solvent reduction was investigated in molten LiF⿿CaF2⿿Li2O between 900 °C and 1040 °C. Nd2O3 galvanostatic electrolyses were performed and reaction products were analyzed by SEM, XRD and electron-probe microscopy. Metallic neodymium was not directly obtained, due to several limitations for Nd2O3 reduction: low electrical conductivity, unfavourable Pilling⿿Bedworth coefficient and formation of a dense insulating CaO layer on the sample surface. Consequently, the reduction of a pellet made of a neodymium oxide-metallic oxide mixture was carried out as an alternative pathway. Nd2O3-CuO reduction led to metallic neodymium production in the form of liquid Cu-Nd alloys. A reaction mechanism was proposed based on these experimental results

Manual for use of Al-containing residues in low-carbon mineral binders

Our society can no longer be imagined without its modern infrastructure, which is inevitably based on the use of various mineral and metallic materials and requires a high energy consumption. Parallel to the production of materials, as well as the production of electricity, huge amounts of various industrial and mining residues (waste/by-product) are generated and many of them are sent to landfill. The European Union (EU) aims to increase resource efficiency and the supply of ”secondary raw materials“ through recycling [1], inventory of waste from extractive industries [2], and waste prevention, waste re-use and material recycling [3]. Much of the industrial and mining waste is enriched with aluminium (Al) and therefore has a potential to replace natural sources of Al in mineral binders with a high Al demand. However, the use of industrial residue in mineral binders requires an extensive knowledge of its chemical composition, including potential hazardous components (e.g. mercury), mineral composition, organic content, radioactivity and physical properties (moisture content, density, etc.). This manual addresses the legislative aspects, governing the use of secondary raw materials in construction products, description of the most common Al-containing industrial and mining residue (bauxite deposits, red mud, ferrous slag, ash and some other by products from industry), potentiality for their reutilisation and its economic aspects, potential requirements/barriers for the use of secondary raw materials in the cement industry and a description of belite-sulfoaluminate cements, which are a promising solution for implementing the circular economy through the use of large amounts of landfilled Al-rich industrial residue and mining waste cement clinker raw mixture. This manual was prepared by partners of the RIS-ALiCE project. It provides a popular content, which targets relevant stakeholders as well as the wider society. Moreover, it offers education material for undergraduate, master and PhD students.Other links: [http://www.zag.si/dl/manual-alice.pdf

Récupération du platine contenu dans les piles à combustible basse température par voie hydrométallurgique Platinum Recovery from used PEMFC by hydrometallurgy

La récupération du platine contenu dans la couche catalytique des piles à combustible est nécessaire pour viabiliser cette technologie vers le secteur industriel. Dans cette étude la voie purement hydrométallurgique a été privilégiée au procédé de récupération pyrométallurgique, évitant la destruction des autres constituants de la pile (membrane, …) et limitant la formation de gaz toxique. Le procédé mise en œuvre est constitué d'une étape de lixiviation à partir d'un mélange HCl/HNO3, suivie par la précipitation d'un sel de platine (NH4)2PtCl6 pouvant soit servir à la synthèse d'un nouveau catalyseur soit à l'obtention de platine métallique. Sur l'ensemble de la chaîne un rendement de récupération de plus de 80 % a pu être obtenu mettant en avant le potentiel de cette stratégie. <br> The recovery of platinum in the catalyst layers of PEMFCs (proton exchange membrane fuel cells) is required to allow a transfer in industry. In this study, hydrometallurgical route was preferred to pyrometallurgical process, reducing both the destruction of the other components of the cell (membrane, …) and the formation of hazardous gas. In this work, the process includes a leaching step from a diluted aqua regia solution, followed by a precipitation step of platinum under the (NH4)2PtCl6 form. This salt can be used either for the synthesis of a new catalyst or to obtain a metallic platinum. Considering these steps the recovery efficiency has been found to be over 80 %, which bring out the potential of this strategy

Récupération du platine contenu dans les piles à combustible basse température par voie hydrométallurgique

La récupération du platine contenu dans la couche catalytique des piles à combustible est nécessaire pour viabiliser cette technologie vers le secteur industriel. Dans cette étude la voie purement hydrométallurgique a été privilégiée au procédé de récupération pyrométallurgique, évitant la destruction des autres constituants de la pile (membrane, …) et limitant la formation de gaz toxique. Le procédé mise en œuvre est constitué d'une étape de lixiviation à partir d'un mélange HCl/HNO3, suivie par la précipitation d'un sel de platine (NH4)2PtCl6 pouvant soit servir à la synthèse d'un nouveau catalyseur soit à l'obtention de platine métallique. Sur l'ensemble de la chaîne un rendement de récupération de plus de 80 % a pu être obtenu mettant en avant le potentiel de cette stratégie

Dispersions d'alumine en milieu aqueux (préparation de suspensions concentrées et mise en forme d'objets par coagulation)

De nouveaux procédés d'élaboration de pièces céramiques de formes complexe, doivent être développés pour s'affranchir des limitations des procédés habituels.Dans ce contexte,le projet qui a conduit ce travail de thèse vise à produire des pièces céramiques directement à la forme et aux cotes finales.Le procédé proposé consiste à couler dans un moule non poreux une suspension très concentrée en poudre et parfaitement fluide,et à consolider la pièce à l'intérieur du moule par coagulation de la suspension,ces deux étapes s'appuyant sur la théorie D.L.V.O au sujet de la stabilité des particules.La stabilisation électrostatique de l'alumine a dans l'eau par ajout d'acide ou de base est influencée par la nature chimique des ions présents dans le milieu.Les contre-ions les plus destructurants vis àvis du solvant tel que CIO4 ou les tétraalkylammonium,conduisent aux dispersions les moins visqueuses.Du fait des effets de dissolution de l'alumine en milieu acide ou basique, la mise en suspension au moyen d'un dispersant anionique est préférée.Le sel de sodium de l'acide 4,5-dihydroxy-1,3-benzènz dizulfonique (1,2(OH)2C6H2 4.5(SO3Na)2.H2O), commercialement appelé Tiron se révèle très efficace en faible concentration (1,3.106 mol.m2) pour stabiliser l'alumine à pH=9 et préparer des suspensions d'une concentration égale à 60% en volume.En utilisant des molécules dérivées du Tiron,le rôle de chaque substituant ainsi que le mécanisme de dispersiondu Tiron ont été identfier en confrontant des mesures d'adsorption et les propriétés électrocinétiques des suspensions.L'étape de coagulation repose sur la réaction de décomposition thermique, de l'acétate d'aluminium (Al(OH)(CH3COO)2) introduit dans la suspension avant le coulage.Des études sur la cinétique de la réaction et sur les propriétés rhéologiques des suspension permettent de déterminer les conditions optimales d'utilisation de cet additif.Par ailleurs, il est montré que la production d'ions trivalents Al3+ dans le milieu induit la désorption du dispersant et augmente considérablement la force ionique, favorisant ainsi la déstabilisation de la suspension.Enfin, la fabrication de pièces de forme complexe confirme les atouts et la potentialité de ce procédé.LIMOGES-ENSCI (870852305) / SudocSudocFranceF

Sintering Ce-TZP/alumina composites using aluminum isopropoxide as a precursor

International audienceA homogeneous 12Ce-TZP/30 vol% Al$_2$O$_3$ composite material has been manufactured by pressureless-sintering in air green compacts of a powder mixture incorporating aluminum isopropoxide as an organic precursor. Densification of the composite material occurs by grain boundary diffusion and is controlled by the diffusion of Ce cations

Influence of debinding and sintering conditions on the composition and thermal conductivity of copper parts printed from highly loaded photocurable formulations

International audienceMetal 3D printing based on the photopolymerization reaction (Digital Light Processing DLP) of an organic matrix in which metal particles are embedded is a developing technology. This technology requires a step of resin removal and densification by sintering to obtain a metal part. This process has been applied to copper. Photocurable formulations with a high loading rate of copper powder of 60 vol.% were developed and suitable for DLP printing with thicknesses>25 µm. Debinding and sintering cycles were investigated on specimens fast cured by gamma irradiation to save materials and time. A debinding in air at 400 °C and sintering in hydrogen lead to a C content of 0.018 wt.%, similar to the raw copper powder and slightly higher oxygen content. The low thermal conductivity of 250 W·m-1·K-1 highlighted the harmful effect of phosphorus from the powder and photoinitiators such as BAPO. The C and O contents and the thermal conductivity measured on copper parts printed by DLP confirm the results obtained on specimens cured by gamma irradiation

Anode-supported single-chamber SOFC for energy harvesting from exhaust gases of thermal engine

National audienceSolid oxide fuel cells operating in mixed gas atmospheres (Air /hydrocarbon mixture), the so-called single chamber SOFCs (SC-SOFCs), are based on the same working principle as the conventional “two-chambers” SOFCs, but the absence of sealing between the two compartments provides an easier operation. This configuration has several advantages over conventional SOFCs. Indeed, new cell geometries, stack assembly and miniaturization of cells are more easily conceivable, opening the way to new applications such as energy recovery in the exhaust gas by conversion of unburned hydrocarbons into electricity. This forward-looking energy recovery system could be applicable to automotive vehicles as well as to plants. Yano et al. and Nagao et al. in 2008 demonstrated the feasibility of such a device by investigating a stack of 12 cells, electrolyte supported Ni-SDC/YSZ/LSM SC-SOFCs, incorporated at the exit of a scooter engine. However, optimization of the system including architecture, gas mixture and materials modification may lead to enhanced performances.In this study, a gas mixture closer to real exhaust conditions has been selected. It is composed of hydrocarbons (HC: propane and propene), oxygen, carbon monoxide, carbon dioxide, hydrogen and water. Only oxygen content has been varied leading to different gas mixtures characterized by the ratio R=HC/O2. Concerning the cell components, a cermet composed of nickel and the electrolyte material, Ce0.9Gd0.1O1.95 (GDC) is used as anode and two cathode materials, Pr2NiO4+δ (PNO) and La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF), have been selected. Anode support is prepared by tape casting; then electrolyte material is screen-printed on top of the green tape previously cut into 22.5 mm diameter discs. Cathode and gold mesh screen printing and sintering conclude cell preparation. These cells have then been tested in various gas mixtures for temperatures ranging from 400°C to 600°C. Ni-GDC/GDC/LSCF-GDC cell operation has delivered a maximum OCV of 706 mV and a power density reaching 16mW/cm² at 500°C with R=HC/O2=0.21. The performances of 22.5 mm diameter cells in various configurations will be presented as well as preliminary results on larger cells (5*5cm2) both in single cell and stack configuration

Anode-supported single-chamber SOFC for energy recovery from exhaust gases of thermal engine

International audienceSolid oxide fuel cells working in a mixed gas atmosphere (fuel and oxidant), the so-called single chamber SOFCs (SC-SOFCs), have been increasingly studied in the past few years. The absence of sealing between the two compartments provides an easier operation than a classical two-chambers SOFC. Hydrogen-air mixtures are not commonly used under single chamber conditions because of their high reactivity and risk of explosion. Therefore, hydrocarbons are preferentially used as fuel. The single chamber configuration has several advantages over conventional SOFCs: new cell geometries, stack assembly and miniaturization of cells are more easily conceivable. These advantages open the way to new applications such as energy recovery in the exhaust gas by conversion of unburned hydrocarbons into electricity, for that purpose, cells would be embedded at the exit of the engine. This forward-looking energy recovery system could be applicable to automotive vehicles as well as to plants. Yano et al. and Nagao et al. in 2008 demonstrated the feasibility of such a device by investigating a stack of 12 electrolyte supported Ni-SDC/YSZ/LSM SC-SOFCs incorporated at the exit of a scooter engine. However, optimization of the system including architecture, gas mixture and materials modification may lead to enhanced performances. In this study, a gas mixture closer to real exhaust conditions has been selected. It is composed of hydrocarbons (HC: propane and propene), oxygen, carbon monoxide, carbon dioxide, hydrogen and water. Only oxygen content has been varied leading to different gas mixtures characterized by three ratios R=HC/O2. Concerning the cell components, a cermet composed of nickel and the electrolyte material, Ce0.9Gd0.1O1.95 (GDC) is used as anode and two cathode materials, Pr2NiO4+δ (PNO) and La0.6Sr0.4Co0.2Fe0.8O3-δ(LSCF), have been selected. Anode support is prepared by tape casting; electrolyte material is then screen-printed on top of the green tape previously cut into 22.5 mm diameter discs. Half cells are co-sintered at 1400°C for 6 hours. Cathode and gold mesh screen printing and sintering conclude cell preparation. These cells have then been tested in the three gas mixtures for temperatures ranging from 400°C to 600°C. Ni-GDC/GDC/LSCF-GDC cell operation has delivered a maximum OCV of 706 mV and a power density reaching 16mW/cm² at 500°C and R=HC/O2=0.21. These results are close to 20 mW/cm², the power density obtained at higher temperature (800°C) by Yano and Nagao during their single cell tests in a R=HC/O2=0.8 gas mixture composed of 4000 ppm of hydrocarbons (methane, ethane, propane and butane) and 5000 ppm of oxygen. In the present project, cathode materials will be compared regarding the cell performances and some improvements are in progress concerning more particularly the cell microstructure