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Implementing MOF-derived Nickel Catalysts as Anion- Exchange Membrane Fuel Cell Anode
No full textInternational audienceDue to their acidic environment, the present generation of proton-exchange membrane fuel cells (PEMFC) requires precious metal catalysts, in particular platinum, which is an obstacle to their large-scale deployment. In contrast, anion-exchange membrane fuel cells (AEMFCs) operate at high pH, facilitating the use of sustainable precious metal free catalysts. While high performance has been reached with platinum-group-metal (PGM) free cathodes in AEMFCs, the replacement of PGM-based anodes by PGM-free ones is a challenge. Nickel-based catalysts are the most promising PGM-free hydrogen oxidation reaction (HOR) catalysts in alkaline medium, but nickel suffers from early surface oxidation at potentials above 0.1 V vs. the reversible hydrogen electrode, which in turn blocks the HOR. In order to mitigate the surface oxidation of nickel at HOR potentials, two main approaches are studied in the literature: optimization of nickel intrinsic properties by alloying with other earth abundant elements, or core@shell nanostructuration of nickel by a protective carbon shell. We will report on recent results obtained with this second approach, and the preparation of core@shell Ni@NC catalysts, comprising a nitrogen-doped carbon shell, via the annealing of Ni-based MOFs. The latter were obtained either by autoclave or by a solvent-free mechanochemical synthesis. Our observations confirm the significant effect of pyrolysis atmosphere (NH3, H2, N2 and combinations) on the HOR activity. Other synthesis parameters will be shown to play a key role on the MOF structure and morphology as well as on the HOR activity of final materials. The materials were characterized by X-ray diffraction, electron microscopy, nitrogen adsorption, X-ray photoelectron spectroscopy (XPS), and electrochemical techniques, including AEMFC tests. The presentation will correlate the material’s structure to their activity and stability. In particular, it will be shown that Ni-based anodes require a specific break-in protocol to show any performance in AEMFC
Investigating the densification of Li6PS5Cl solid electrolyte through multi-scale characterization techniques
No full textInternational audienceLi 6 PS 5 Cl (LPSCl) has recently gained attention as a promising solid-state electrolyte for batteries. However, the mechanisms underlying the "cold sintering" process in LPSCl remain poorly understood. In this study, we performed in situ densification of LPSCl while simultaneously measuring electrochemical impedance spectroscopy and micro-tomography to gain deeper insights into "cold sintering" process and to correlate the ionic conduction with the three-dimensional microstructure of the solid electrolyte. We observed that the large (secondary) particles are fracturing, while the grain boundary (GB) conductivity is improving due to better contact between grains. We have found that during the pressure application (up to 510 MPa from 76.2 MPa) at room temperature, the conductivity increases 2.45 times (up to 1.66 mS cm -1 ). From an in-depth electrochemical impedance and quasielastic neutron scattering (QENS) investigation, we show that the conductivity enhancement primarily arises from improved GB contact, with the bulk material remaining largely unaffectedthat is, unsintered. However, the Li + conductivity is not limited by bulk but by GB resistance. The electrolyte's conductivity without any GB contribution is estimated from QENS results with the Nernst-Einstein equation to be 5.3 mS cm -1 , giving us the maximum conductivity that could be reached with shaping without modifying the bulk of the material
GW250114: Testing Hawking’s Area Law and the Kerr Nature of Black Holes
No full textInternational audienceThe gravitational-wave signal GW250114 was observed by the two LIGO detectors with a network matched-filter signal-to-noise ratio of 80. The signal was emitted by the coalescence of two black holes with near-equal masses m_{1}=33.6_{-0.8}^{+1.2}M_{⊙} and m_{2}=32.2_{-1.3}^{+0.8}M_{⊙}, and small spins χ_{1,2}≤0.26 (90% credibility) and negligible eccentricity e≤0.03. Postmerger data excluding the peak region are consistent with the dominant quadrupolar (ℓ=|m|=2) mode of a Kerr black hole and its first overtone. We constrain the modes' frequencies to ±30% of the Kerr spectrum, providing a test of the remnant's Kerr nature. We also examine Hawking's area law, also known as the second law of black hole mechanics, which states that the total area of the black hole event horizons cannot decrease with time. A range of analyses that exclude up to five of the strongest merger cycles confirm that the remnant area is larger than the sum of the initial areas to high credibility
Fabrication of visualized NO gas sensing system operable at near room temperature
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Identifying malaria epidemic periods in Togo by health district and target group: a generalised additive model approach
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Evaluation of commercial pure conductive copper pastes by screen printing for a-Si:H/c-Si heterojunction solar cells
No full textInternational audienceThis paper investigates the feasibility of using commercial copper (Cu) pastes as an alternative to silver (Ag)-based pastes in the metallization of silicon heterojunction (SHJ) solar cells. While SHJ technology has emergedas a promising option for high-efficiency solar cells, the reliance on Ag presents significant challenges due to itsscarcity and cost. This study identifies that the tested cells printed using Cu pastes demonstrate inferior overallperformance compared to full Ag and Ag/Cu pastes. To understand the underlying causes of this performancedisparity, a series of experiments were conducted. Notably, no degradation in cell performance associated withCu-induced defects in silicon was found, even after annealing at 200 °C extended to 40 min. The contact resistivityof the commercial Cu pastes was found to be comparable to that of Ag pastes, with even better performanceunder certain annealing conditions. However, the higher resistance (Rline) of the Cu lines remained a critical issue.Microscopic analysis revealed a significantly smaller cross-sectional area for the analyzed Cu lines printedthrough the same screen openings, although this alone did not fully explain the observed differences in Rline. Annealingunder Ar (a low/no oxidation condition) allowed to reduce by 60 % one Cu paste Rline, staying insufficientto compete with reference Ag-based pastes but emphasizing the influence of oxidation. These preliminaryfindings address the challenges associated with replacing Ag contacts with Cu by screen printing in the metallizationof SHJ solar cells
Unveiling the relationship between the energy released during thermal runaway of Li-ion cells and their stored electrical energy
No full textInternational audienceThe use of lithium-ion (Li-ion) batteries has rapidly increased due to improvements in performance, durability, and cost-effectiveness, driven by the growth of electric vehicles (EVs), renewable energy storage, and portable electronics. High energy density, long cycle life, and low self-discharge rate are key factors behind this evolution. However, the safety of Lithium-ion batteries remains a major concern due to the potential risk of thermal runaway, which can result in fast heat release, the ejection of particles and gases, and possibly fire and explosion. Therefore, the reliable characterization of thermal runaway energy and gas volume release is essential for incorporating thermal runaway mitigation into the design phase of battery modules. In this study, 29 thermal runaway tests of large-capacity prismatic and pouch NMC cells were analysed to generate thermal runaway energy and gas volume release. It was found that thermal runaway energy, when normalized by the electrical energy of the cell at the time thermal runaway occurs, was constant during all the tests performed under vacuum and inert atmosphere. The constant was equal to 1.25. Similarly, the normalized number of moles generated during thermal runaway remained constant at 4.9 x 10-3 mol·kJ-1. When the tests were conducted in air, the large quantity of oxygen available led to additional combustion and energy release. The normalized thermal runaway energy increased to 5.0, while the normalized number of moles decreased to 4.2 10-3 mol·kJ-1. The two conditions-under vacuum and in air- represent the two cases limiting the access of air in a typical battery module configuration, therefore the data presented in this work can be useful for evaluating thermal runaway propagation and casing integrity in a battery module during the design phase
Kinetics of Hydrogen Absorption in Individual α-Phase Palladium Nanoparticles
No full textInternational audiencePalladium hydrogen is a useful model in the study of both hydrogen absorption for energy storage, and lattice gas systems for fundamental thermodynamic models.Using in situ time-resolved X-ray nanodiffraction at the fourth generation Extremely Brilliant Source of the European Synchrotron (ESRF-EBS), the kinetics of hydrogen absorption in individual α phase Pd nanoparticles is examined. Hydrogen absorption kinetics in a gas reactor and an electrochemical cell are compared. Combining the individual nanoparticle X-ray measurements with chronoamperometry measurements, the kinetics of the ensemble of Pd nanoparticles on the glass carbon substrate is compared with kinetics at the single nanoparticle level. Hydrogen absorption in α phase Pd in the electrochemical system is found to be slower than that of the gas system. Furthermore, the absorption in the electrochemical system slows down as the electrochemical potential is lowered. This slow down is found to be directly related to the increasing hydrogen absorption per step in electrode potential. Furthermore, differences between absorbed-quantity normalized absorption times is seen between the hydrogen and deuterium absorbates. Sieverts's law of absorption is also shown to hold for individual Pd nanoparticles in the α phase.</div
Un fort séisme récent dans les Alpes du Sud ?
No full textLettre d'information N°4, mai 2025, https://www.epos-france.fr/valorisation/lettre-dinformation-epos-france/L’analyse d’images aériennes a mis en évidence un escarpement continu sur environ 3 km de long au col de Lombarde (proche de la station d’Isola 2000 dans les Alpes du Sud). Dans le cadre de l’action FACT (Faille Active en France,Epos-France), 2 tranchées paléosismologiques ont été réalisées le long de l’escarpement et sont en cours d’analyse. Les premiers résultats laissent supposer un paléoséisme avec une magnitude de l’ordre de 6,5-7 dans les dernières dizaines de milliers d’années
Search for light pseudoscalar boson pairs produced from Higgs boson decays using the 4 and 22 final states in proton-proton collisions at = 13 TeV
No full textInternational audienceA search for a pair of light pseudoscalar bosons (a) produced in the decay of the 125 GeV Higgs boson is presented. The analysis examines decay modes where one a decays into a pair of tau leptons and the other decays into either another pair of tau leptons or a pair of muons. The a boson mass probed in this study ranges from 4 to 15 GeV. The data sample was recorded by the CMS experiment in proton-proton collisions at a center-of-mass energy of 13 TeV and corresponds to an integrated luminosity of 138 fb. No excess above standard model (SM) expectations is observed. The study combines the 4 and 22 channels to set upper limits at 95% confidence level (CL) on the product of the Higgs boson production cross section and the branching fraction to the 4 final state, relative to the Higgs boson production cross section predicted by the SM. In this interpretation, the a boson is assumed to have Yukawa-like couplings to fermions, with coupling strengths proportional to the respective fermion masses. The observed (expected) upper limits range between 0.007 (0.011) and 0.079 (0.066) across the mass range considered. The results are also interpreted in the context of models with two Higgs doublets and an additional complex singlet field (2HD+S). The tightest constraints are obtained for the Type III 2HD+S model. In this case, assuming the Higgs boson production cross section equals the SM prediction, values of the branching ratio for the Higgs boson decay into a pair of a bosons exceeding 16% are excluded at 95% CL for a boson masses between 5 and 15 GeV and 2, with the exception of scenarios in which the a boson mixes with charm or bottom quark-antiquark bound states