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Cation Contamination Redistribution throughout the PEMFC MEA: Towards the Establishment of Regeneration Protocols
No full textInternational audienceProton exchange membrane fuel cells (PEMFCs) are a promising technology for automotive applications. The membrane electrode assembly (MEA) remains the most vulnerable element in fuel cells due to its membrane composed of perfluorosulfonic acids. Over the lifetime of the PEMFC, cation contamination occurs from corrosion of fuel cell stack components such as bipolar plates and could be concentrated at particular locations. These cations can migrate from the bipolar plate into the electrode and the membrane. Indeed, due to their affinity toward sulfonic groups, they tend to replace protons affecting membrane conductivity. In addition, some ionic species such as iron cations are commonly known as catalysts for the Fenton reaction responsible for the chemical degradation of the membrane.In this work, we investigate the local effect of ferric contamination and its diffusion through electrochemical tests and post-mortem analyses. A membrane is strategically contaminated by Fe3+ ions, then assembled into MEA using a hot-pressing method. A segmented cell monitors the ferric ion impact on local cell performance and impedance parameters at different operating conditions. After in-situ tests, MEA’s membrane and gas diffusion electrodes (GDE) are separated for analysis. Then, iron species are quantified to visualize the migration of Fe3+ in both in- and through-plane directions.Post-mortem analysis suggests that at high local contamination, a part of cations is leached from the contaminated regions of the membrane after a PEMFC operating (Figure 1). In terms of cation distribution, post-mortem analyses reveal a preferential diffusion of Fe3+ perpendicular to the gas diffusion channels and in the flow direction of H2. On a local scale, performances of contaminated channels are affected especially at low hydration levels Besides the in-plane diffusion the propagation of cations from the membrane to electrodes has been detected, at rates approaching 25% of total contamination. The impact of the Fe3+ migration on radical scavenger diffusion is discussed. Our results provide useful information about cation diffusion in complex systems such as MEAs and gives us some hints on recovery protocols to extend lifetime of fuel cells
Polyester-based Polymer Electrolytes with an Extended Electrochemical Stability Window for Solid-State Lithium Metal Batteries
No full textInternational audiencePolymer electrolytes (PEs) have been developed to circumvent the safety issues of the organic liquid electrolytes which are flammable and volatile. Many polymers such as polyetheres, polycarbonates, fluoropolymers etc.1 have been investigate with different lithium salts. However, only few of them could provide good ionic conductivity in solvent/plasticizer-free conditions. Poly(ethylene oxide) (PEO)-based materials are one of the most important PEs for lithium-ion batteries due to their flexible structures and ability to dissolve the lithium salts resulting in PE with high conductivity at temperature above their melting point. Nevertheless, the PEO-based PEs are facing critical challenges when applied with high energy density batteries. On one hand, the PEO-based PEs suffered from the oxidation of the ether bond at ~ 4 V vs. Li+/Li which does not meet the voltage window of high energy positive electrodes such as LiNixMnyCo1-x-yO2 (NMC) and LiMnxFe1-x PO4 (LMFP) and thus these PEs are usually reported with only LiFePO4 (LFP) positive electrodes.2 Therefore, developing polymer electrolytes with wider electrochemical stability window (ESW) and high ionic conductivity is one of the major tasks to realize solid-state Li-metal batteries with high energy density. The replacement of PEO-based PEs with polyester-based PEs3,4 could be a promising candidate to improve the voltage limitation. In this work, we report solid-state PE based on crosslinked poly(butyl malonate) (CPBM) and lithium salts. The polymalonate polymers was crosslinked with an in-situ Michael addition reaction, yielding a 3D network with tunable crosslinking degree. As compared to PEO-base PEs, the fully amorphous and self-standing CPBM-based PEs exhibited comparable conductivities but much higher Li transfer numbers (>0.6) and limiting current density (~0.7 mA cm-2), which is ideal for efficient ion transport. Moreover, these PEs showed a wide electrochemical stability window up to 4.7 V vs. Li/Li+. The good electrochemical stability of CPBM-based PEs was confirmed by long-term cycling stability in both Li stripping/plating tests and full cells with LFP and LMFP electrodes at high current densities. We believe that polymalonate-based PEs could be a promising choice to overcome the voltage limitation of PEO-based PEs and realizing safe lithium metal batteries with high performance.References1 Li, J. et al. Adv. Energy Mater. 11, 2003239 (2021)2 Yang, X. et al. Energy Environ. Sci. 13, 1318–1325 (2020)3 Chen, L. et al. Chem. Mater. 31, 4598–4604 (2019)4 Yu, X. et al. ACS Energy Lett. 7, 3791–3797 (2022
How are scientific knowledge and risk management of glacial and periglacial processes influenced by Alpine catastrophic events ?
No full textInternational audienceMass movements of glacial and periglacial origin intensify with the climate crisis. Consequently, attempts are being made to inventory these events by hazard type or region. The scientific literature increasingly focuses on understanding causes, failure mechanisms, and propagation of recent and past events. Less attention is given to the characterisation of comprehensive risk management.We have therefore created an Alpine database of ice avalanches, GLOFs, debris flows, rock falls and rock avalanches that have threatened valleys in the last centuries. The selected events are those that required advanced scientific research and/or risk management in order to better understand glacial and periglacial processes. Our research aims to contextualize the events temporally, as they occur at given time and climate, and spatially, the high Alpine regions being distributed over different countries. We have also adopted a social approach since the events exist as elements perceived and interpreted by societies. Since a phenomenon becomes an event if society considers it to be a risk, we can ask ourselves how it is considered by society. Through a geochronology derived from the database (c. 200 events selected in more than 120 watersheds), we try to understand how glacial and periglacial hazards are perceived and considered from the risk management perspective. Over the past 20 years, this management at national and international levels has intensified, moving from a local approach to a wider, organized, and multi-disciplinary approach
Measurement of Exclusive --argon Interactions Using ProtoDUNE-SP
No full textInternational audienceWe present the measurement of --argon inelastic cross sections using the ProtoDUNE Single-Phase liquid argon time projection chamber in the incident kinetic energy range of 500 -- 800 MeV in multiple exclusive channels (absorption, charge exchange, and the remaining inelastic interactions). The results of this analysis are important inputs to simulations of liquid argon neutrino experiments such as the Deep Underground Neutrino Experiment and the Short Baseline Neutrino program at Fermi National Accelerator Laboratory. They will be employed to improve the modeling of final state interactions within neutrino event generators used by these experiments, as well as the modeling of --argon secondary interactions within the liquid argon. This is the first measurement of --argon absorption at this kinetic energy range as well as the first ever measurement of --argon charge exchange
Peatland trees record strong and temporally stable hydroclimate information in tree-ring δ 13 C and δ 18 O
No full textInternational audienceAbstract. Peatland trees are valuable archives of paleoclimatic information; however, gaps persist in understanding the relationships between tree growth, peatland hydrology, and hydroclimate variables. While previous research in peatlands has mainly focused on tree-ring widths (TRW), yielding inconclusive results, the potential of stable carbon (δ13C) and oxygen (δ18O) isotopes in tree rings remains unexplored. In this study, we develop TRW, δ13C, and δ18O chronologies of Scots pine trees located in a Swedish peatland and a reference site on bedrock with a mineral soil layer. We assess their responses to hydroclimate conditions and evaluate their potential for reconstructing hydroclimate variations. Our findings show significant differences in mean TRW and δ13C values between the peatland and reference sites. Moreover, while TRWs do not exhibit distinct common patterns between sites, both δ13C and δ18O site chronologies show uniform year-to-year variations across all sites. Some discrepancies for TRW and δ13C site chronologies emerge, however, regarding multi-decadal trends. While the climate sensitivity of TRW is weak and non-homogenous, the δ13C and δ18O peatland and reference chronologies contain robust and consistent signals, with a maximum sensitivity to water table, precipitation, and vapor pressure deficit (VPD) variations during summer. Both δ13C and δ18O chronologies show stable relationships with three key hydroclimate variables over time. In conclusion, while TRWs from living peatland pines at our sites have limited potential to record high-frequency hydroclimate information, δ13C and δ18O chronologies can serve as excellent proxies for the reconstruction of past hydroclimate changes
De la glace souterraine au-delà des limites de la cryosphère. Fonctionnement glaciologique et usages de la Grande Glacière du Parmelan (massif des Bornes, France)
No full textInternational audienceWithin the cryosphere, ice caves are among the least well-known features. These caves have morphologies that create micro-climatic conditions favorable for the development or maintenance of perennial ice accumulations. Very little research has been conducted in France on these forms of permafrost, which can be described as “azonal.” The aim of this research is to use a multi-method approach to understand the glaciological and thermal dynamics over the course of a year, as well as the uses and paleoenvironmental potential of a mid-altitude ice cave in the Alps: the Grande Glacière du Parmelan (1605 m a.s.l., Bornes Massif, Haute-Savoie, France). A topographic survey using terrestrial laser scanning revealed the current presence of at least 8,800 m³ of ice, within which wood has been dated (14C) to between 1260 ± 30 BP and 120 ± 30 BP, highlighting the potential role of ice caves as paleoenvironmental archives. While the ice of the Grande Glacière was a renewable and exploited resource in the past, monitoring has shown losses in thickness ranging from several centimeters to several decimeters within a single year, despite some local accumulations of seasonal ice. Connected to the underlying karstic network (known as a ‘dynamic’ ice cave), which tends to warm, and with an average annual temperature of around 0 °C, the Grande Glacière appears to be close to a tipping point.Au sein de la cryosphère, les glacières sont parmi les objets les moins bien connus. Il s'agit de grottes ou de gouffres dont la morphologie permet des conditions micro-climatiques favorables au développement ou au maintien d'accumulations de glace pérennes. Très peu de recherches ont été effectuées sur le territoire français sur ces formes de permafrost que l' on peut qualifier d'azonal. Cet article entend comprendre, à travers une approche multi-méthode, les dynamiques glaciologiques et thermiques sur une année ainsi que les usages et le potentiel paléoenvironnemental d'une glacière de moyenne altitude dans les Alpes : la Grande Glacière du Parmelan (1605 m d'altitude, massif des Bornes, Haute-Savoie, France). Un levé topographique par balayage laser terrestre a montré la présence actuelle d'au moins 8800 m 3 de glace à l'intérieur de laquelle des bois ont été datés ( 14 C) entre 1260 ± 30 BP et 120 ± 30 BP, rappelant le rôle potentiel d'archives paléo-environnementales des glacières. Si la glace de la Grande Glacière a été une ressource renouvelable et exploitée par le passé, le suivi a montré des pertes d' épaisseur pluricentimétrique à pluridécimétrique en une année, malgré quelques accumulations locales de glace saisonnière. Connectée au réseau karstique sous-jacent (glacière dite « dynamique ») qui tend à la réchauffer et présentant une température moyenne annuelle autour de 0 °C, la Grande Glacière semble proche d'un point de bascule
Electronic transport simulations of Ni/graphene, hBN, MoSe2 /Ni vertical junctions
No full textInternational audienceWe simulate the electronic and transport properties of metal/two-dimensional material/metal vertical heterostructures, with a focus on graphene, hexagonal boron nitride and two phases of molybdenum diselenide. Using density functional theory and non-equilibrium Green’s function, we assess how stacking configurations and material thickness impact important properties, such as density of states, potential barriers and conductivity. For monolayers, strong orbital hybridization with the metallic electrodes significantly alters the electronic characteristics, with the formation of states within the gap of the semiconducting two-dimensional materials. Trilayers reveal the critical role of interlayer coupling, where the middle layer retains its intrinsic properties, thus influencing the overall conductivity. Our findings highlight the potential for customized multilayer designs to optimize electronic device performance based on two-dimensional materials
Comparison of Automated ERT stations (A-ERT) for continuous monitoring electrical resistivity in polar and mountain permafrost regions
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Boron doped nanocrystalline silicon: understanding a tricky material for high performance heterojunction solar cells
No full textInternational audienceThe best silicon heterojunction (SHJ) solar cells show the potential of nanocrystalline silicon (nc-Si:H) to improve their performance on both the emitter and BSF (back surface field) sides. However, in production, nc-Si:H presents several challenges, particularly in terms of deposition rate, reproducibility and stability of layers and interfaces. This work presents a comprehensive study using advanced characterization of the properties of (p) nc-Si:H films grown in an industrial scale equipment. We have focused on studying different thicknesses and the impact of annealing on our layers, although we need very thin nc-Si:H layers to avoid parasitic absorption and reduce deposition time. Above 40 nm nc-Si:H seems to crystallize and stabilize its properties, while below this thickness we deal with a transition phase with evolution in crystalline fraction and properties giving a more unstable material. On the other hand, blisters appeared on layers with thicknesses over 60 nm due to hydrogen accumulation and material stress. Understanding the material properties can serve not only for SHJ but also for TCO-free recombination junction in tandems using nc-Si:H layers
Comprendre la filière « lait d’équidé »
No full textInternational audienceLe lait de jument et d’ânesse séduit de plus en plus par ses qualités nutritionnelles et ses usages variés, allant de l’alimentation infantile aux cosmétiques. Le nombre de producteurs de lait d’équidés augmente doucement depuis les années 2000.Mais qui sont réellement les producteurs derrière cette filière encore peu connue ?Comment ceux-ci construisent des modèles d’exploitation, et quels sont ces modèles ?Cette webconférence propose un panorama riche à travers les résultats d’une étude menée par l’IFCE, complétée par les données du réseau équin et le témoignage concret d’un exploitant. Se basant notamment sur divers échanges (discussions, entretiens) et observations de terrain avec les professionnels, elle abordera les enjeux techniques, économiques et éthiques de la production, les profils des éleveurs engagés, ainsi que les stratégies choisies pour vivre de cette activité. Elle mettra en avant l’expérience précise d’un producteur, pour un ancrage certain dans la réalité vécue. L’occasion de mieux comprendre les spécificités et le potentiel de cette filière émergente