Fine insight on high temperature hydrogen attack initiation and morphology on case studies

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Spacers to improve performance and porosity of graphene based polymer electrolyte fuel cells

Graphene has been suggested as a potential support material to replace commercial carbon black due to its carbon corrosion resistance. However, graphene-based electrodes typically perform poorly in MEA testing due to restacking of the graphitic sheets. In this study we investigate the introduction of carbon black and their effects on the porosity and current density of graphene-based supports

Caractérisation de l\u27état d\u27engagement de l\u27azote au cours du process de transformation d\u27aciers calmés à l\u27aluminium - Conséquences sur les propriétés d\u27emboutassibilité après recuit continu.

L\u27utilisation des tôles d\u27acier bas carbone clamés aluminium dans l\u27industrie automobile impose des exigences en terme de comportement mécanique, en particulier pour pouvoir être embouties. Cette thèse a pour but de mieux comprendre le rôle de l\u27azote lors des recuits continus. Pour connaître cet effet, il faut, tout d\u27abord, pouvoir caractériser et quantifier les différents états de l\u27azote (N en solution ou N précipité). Nous avons donc mis au point une méthode de dosage de l\u27azote en solution par mesure de Pouvoir Thermo-Electrique (PTE). Les résultats ont été comparés à ceux obtenus par d\u27autres techniques. Les dosages par PTE se sont avérés fiables et plus aisés à mettre en uvre. Il faut également connaître l\u27état de précipitation de l\u27azote aux différentes étapes de la chaîne de fabrication de l\u27acier, en particulier lors du bobinage. Ainsi, des cinétiques de précipitation de l\u27azote, par PTE, ont montré que tout l\u27azote a précipité en 10 min à 700 degrés C. Des études en MET ont mis en évidence 2 types de nitrures : (Al,Cr)N de structure NaCl et AIN de structures wurtzite. Il semblerait que le laminage à chaud soit une condition nécessaire à la formation des précipités de (Al,Cr)N. Nous avons par le suite, mis en évidence les influences respectives de l\u27azote et du carbone sur la recristallisation. Pour cela, plusieurs traitements thermiques sur tôle à chaud ont été effectués afin d\u27obtenir divers états de précipitation de l\u27azote et du carbone. Il s\u27est avéré que le carbone joue un rôle primordial et l\u27azote un rôle secondaire sauf lorsqu\u27il est engagé sous forme d\u27(Al,Cr)N. Dans ce cas, l\u27azote confère alors une très bonne aptitude à l\u27emboutissage s\u27il est couplé à une faible quantité de carbone en solution solide au court du recuit

Tonalités et couleurs du style dans le « Voyage en Italie » de Chateaubriand

Guetaz Alain. Tonalités et couleurs du style dans le « Voyage en Italie » de Chateaubriand. In: Bulletin de l'Association Guillaume Budé, n°1, avril 1998. pp. 67-86

Advanced Fuel Cell Catalyst based on Graphene

International audienceCarbon blacks supported Pt, currently widely used as electrocatalysts in Polymer Electrolyte Membrane Fuel Cells (PEMFC) are thermochemically unstable in PEMFC operating conditions. This is especially true at the cathode side where, on top of relatively elevated temperature (80°C) and acidic conditions, both the potential and the relative humidity may be high. The resulting carbon oxidation is partially responsible for the PEMFC performance decrease observed over time. Hence, long term durability still needs to be improved in order to consider PEMFC as credible alternatives to conventional power sources for automotive, stationary or portable applications.Much effort have been directed to identify and synthesize alternative carbon materials as catalyst supports for PEMFCs. One strategy to decrease carbon support corrosion is to use carbon with high extent of graphitization, which is supposed to decrease defect sites on the carbon structure, where carbon oxidation starts [1], [2]. However high graphitic content of carbon can be a brake for particle nucleation and dispersion. Among the different forms of carbon, graphene, a monolayer of graphite, has attracted increasing attention because of its unique two-dimensional (2D) single sheet of sp2 carbon in a hexagonal arrangement. Graphene possesses unique properties, such as high charge-carrier mobility (up to 105 cm2 V-1 s-1), super conductivity, ambipolar electric field effect, high mechanical strength (130 GPa), quantum Hall effects at room temperature, and high surface area (2,600 m2 g-1). These properties make graphene ideal for a wide potential applications such as in nanoelectronics, electrode support for catalysts in electrochemical energy systems, chemical and biological sensors, composite materials and biotechnology.Although graphene exhibits an attractive range of properties as catalyst supports for fuel cells (FC), they suffer from a serious issue. Integration of such catalyst in catalyst layer (CL) is complex due to the high cohesive van der Walls attractions between graphene sheets, named also pi-stacking of graphene layers, leading to serious blocking of the active surface area. To overcome this phenomena, one solution consists to add spacers or additives in graphene sheets such as carbon black, carbon nanotube and urea have been reported to be intercalated into Pt/graphene or with several applications in FCs [3]. In this work, platinum catalysts were synthetized on Graphene support, nanocharacterised, processed in ink and incorporated in fuel cell. Several techniques of MEA fabrication were used: CCB (catalyst coated backing), CCM (catalyst coated membrane) or CCM by decal (transfert on inert substrate). We investigated these new active layers at the cathode side in term of electrocatalytic performance and compared the electrochemical properties of these hybrid materials with a commercial Pt/C catalyst using carbon blacks as carbon support. Moreover, the use of additive was also studied to enhance performance by aerate active layer and avoid pi-stacking of graphene layer.The goal of the project is to demonstrate that the use of GRM based carbon supports can be promising in effectively reducing the carbon corrosion and then increase lifetime of the cell. Accelerated stress test has been done in 25cm² fuel cell setup on both AST for carbon support and fuel cell Dynamic Load Cycle, FC-DLC cycles.The GrapheneCore3 European program funds this work.References[1] Lu, Y; Applied Catalysis B: Environmental 199 (2016) 292-314.[2] Yadav, R.; Industrial & Engineering Chemistry Research 57 (2018) 9333-9350.[3] Suter, T. A. M. et al. Nanomaterials 11, 2530 (2021)

Development of exacerbated load cycles as AST for PEMFC stacks and validation by in-situ and ex-situ characterizations

International audienceProton Exchange Membrane Fuel Cell (PEMFC) technologies are considered as a promising and clean energy supply for both transportation and stationary applications. State of art components present performance enabling integration of stacks in actual systems and vehicles. However, durability still needs to be improved as well as overall system cost still needs to be reduced to enable large scale competitive deployment. Assessment of components and stacks durability is thus essential from early stage of development until implementation into systems. To this end, the intention of the European project ID-FAST was to support the development of accelerated stress tests (AST) for automotive application to be validated first on single cells and then on specific stack designs. The methodology selected was to consider as a starting point the performance losses and degradation phenomena induced by ageing tests following a load profile and operating conditions representative of real drive cycles [1]. Next step was to define modified load cycles enabling to exacerbate the degradation and voltage losses induced, while keeping same mechanisms involved thus allowing to reach similar level of performance after a shorter ageing period and less cycles applied

Advanced Fuel Cell Catalyst based on Graphene

International audienceCarbon blacks supported Pt, currently widely used as electrocatalysts in Polymer Electrolyte Membrane Fuel Cells (PEMFC) are thermochemically unstable in PEMFC operating conditions. This is especially true at the cathode side where, on top of relatively elevated temperature (80°C) and acidic conditions, both the potential and the relative humidity may be high. The resulting carbon oxidation is partially responsible for the PEMFC performance decrease observed over time. Hence, long term durability still needs to be improved in order to consider PEMFC as credible alternatives to conventional power sources for automotive, stationary or portable applications.Much effort have been directed to identify and synthesize alternative carbon materials as catalyst supports for PEMFCs. One strategy to decrease carbon support corrosion is to use carbon with high extent of graphitization, which is supposed to decrease defect sites on the carbon structure, where carbon oxidation starts [1], [2]. However high graphitic content of carbon can be a brake for particle nucleation and dispersion. Among the different forms of carbon, graphene, a monolayer of graphite, has attracted increasing attention because of its unique two-dimensional (2D) single sheet of sp2 carbon in a hexagonal arrangement. Graphene possesses unique properties, such as high charge-carrier mobility (up to 105 cm2 V-1 s-1), super conductivity, ambipolar electric field effect, high mechanical strength (130 GPa), quantum Hall effects at room temperature, and high surface area (2,600 m2 g-1). These properties make graphene ideal for a wide potential applications such as in nanoelectronics, electrode support for catalysts in electrochemical energy systems, chemical and biological sensors, composite materials and biotechnology.Although graphene exhibits an attractive range of properties as catalyst supports for fuel cells (FC), they suffer from a serious issue. Integration of such catalyst in catalyst layer (CL) is complex due to the high cohesive van der Walls attractions between graphene sheets, named also pi-stacking of graphene layers, leading to serious blocking of the active surface area. To overcome this phenomena, one solution consists to add spacers or additives in graphene sheets such as carbon black, carbon nanotube and urea have been reported to be intercalated into Pt/graphene or with several applications in FCs [3]. In this work, platinum catalysts were synthetized on Graphene support, nanocharacterised, processed in ink and incorporated in fuel cell. Several techniques of MEA fabrication were used: CCB (catalyst coated backing), CCM (catalyst coated membrane) or CCM by decal (transfert on inert substrate). We investigated these new active layers at the cathode side in term of electrocatalytic performance and compared the electrochemical properties of these hybrid materials with a commercial Pt/C catalyst using carbon blacks as carbon support. Moreover, the use of additive was also studied to enhance performance by aerate active layer and avoid pi-stacking of graphene layer.The goal of the project is to demonstrate that the use of GRM based carbon supports can be promising in effectively reducing the carbon corrosion and then increase lifetime of the cell. Accelerated stress test has been done in 25cm² fuel cell setup on both AST for carbon support and fuel cell Dynamic Load Cycle, FC-DLC cycles.The GrapheneCore3 European program funds this work.References[1] Lu, Y; Applied Catalysis B: Environmental 199 (2016) 292-314.[2] Yadav, R.; Industrial & Engineering Chemistry Research 57 (2018) 9333-9350.[3] Suter, T. A. M. et al. Nanomaterials 11, 2530 (2021)

Development of exacerbated load cycles as AST for PEMFC stacks and validation by in-situ and ex-situ characterizations

International audienceProton Exchange Membrane Fuel Cell (PEMFC) technologies are considered as a promising and clean energy supply for both transportation and stationary applications. State of art components present performance enabling integration of stacks in actual systems and vehicles. However, durability still needs to be improved as well as overall system cost still needs to be reduced to enable large scale competitive deployment. Assessment of components and stacks durability is thus essential from early stage of development until implementation into systems. To this end, the intention of the European project ID-FAST was to support the development of accelerated stress tests (AST) for automotive application to be validated first on single cells and then on specific stack designs. The methodology selected was to consider as a starting point the performance losses and degradation phenomena induced by ageing tests following a load profile and operating conditions representative of real drive cycles [1]. Next step was to define modified load cycles enabling to exacerbate the degradation and voltage losses induced, while keeping same mechanisms involved thus allowing to reach similar level of performance after a shorter ageing period and less cycles applied

Étude de la cinétique de précipitation des nitrures d’aluminium dans un acier bas carbone

Afin de déterminer une technique fiable de dosage des nitrures d’aluminium dans les aciers calmés aluminium, nous avons comparé différentes techniques : les dosages par PTE, par hydrogène à chaud, par dissolution électrochimique suivie d’une minéralisation, par dissolution électrochimique suivie d’une attaque sodique et le dosage de Beeghly. Ces techniques permettent de quantifier soit l’azote en solution solide, soit l’azote précipité. Nous avons étudié différents états de précipitation d’AlN : trois états durant la cinétique de précipitation à 700°C et deux états de réchauffage (1130 et 1250°C). Nous en avons déduit que les trois premières techniques semblent fiables alors que le dosage de Beeghly ne donne de bons résultats que pour les précipités formés à haute température