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Elucidating Pt/C and ionomer aggregation dynamics in the manufacturing of fuel cell catalyst layers: a discrete element method approach
No full textInternational audienceThe production of fuel cells is bottle-necked by the prohibitive cost of one component – the catalyst layer. The goal of manufacturers has been to minimise Pt loading and maximise the electrochemical efficiency, at scale. A mesoscale model is sought-after, to describe the influence of common manufacturing parameters on the microstructure of fuel cell catalyst layers. In this work we propose a novel end-to-end mesoscale modeling workflow to capture the spatial aggregation of carbon support particles against an ionomer-based binder. We use the Discrete Element Method (DEM) to capture the co-aggregation of the carbon-support and binder, as a function of their inter-particle Derjaguin–Landau–Verwey–Overbeek (DLVO) interactions. This model provides insights in the variance in ionomer aggregation as a function of solvent composition. We observe a decrease in ionomer secondary aggregation with decreasing water content. This variance in the local catalyst – ionomer distribution was studied using various micro-structural descriptors
Mineralogical Changes and H2 Generation Yield During Hydrothermal Alteration of a Magnetite‐Siderite Assemblage
No full textInternational audienceTo date, the generation of natural hydrogen (H 2 ) from the alteration of Fe II ‐bearing minerals has mainly been studied through serpentinization in (ultra)mafic rocks. This study explores Banded Iron Formations (BIF), which are rich in Fe II minerals, as a potential source for H 2 . We conducted a hydrothermal experiment at 200°C with a combined magnetite‐siderite assemblage, two major components of BIF. The experiment, designed with a high water‐to‐rock ratio and a gas phase (W‐R = 300) enabled to assess mineral transformations during the alteration. Thermodynamic simulations were finally conducted, to explore H 2 ‐generating yields in more realistic geological scenarios (no gas phase, lower W‐R). Our experimental findings show that H 2 is produced through complete siderite dissolution and magnetite precipitation. Concomitantly, non‐stoichiometric primary magnetite (Fe II /Fe III < 0.5) did not enhance H 2 yield; instead, it acted as a sink for dissolved Fe 2+ , sequestrating about 10% of the iron from siderite without oxidation to recover a more ideal stoichiometry. This suggests that abundant, non‐stoichiometric magnetite in natural settings may reduce H 2 generation yields. Mass balance calculations indicate that 83% of the expected H 2 generated was unaccounted for, consistent with suspected CO 2 reduction and formation of dissolved organic compounds in the fluids. Thermodynamic simulations at varying W‐R ratios (from 300 to 1) reveal that H 2 yield ranges widely (39 mmol–73 μmol H 2 per kg of siderite), since lower W‐R prevent from siderite dissolution and enhance H 2 consumption via carbon reduction. These findings imply that low W‐R ratios in BIF ‐and other siderite‐bearing lithologies, may limit H 2 resources
New Sulfur-Containing Gel Polymer Electrolytes for Sodium–Metal Batteries
No full textInternational audienceA novel sulfurated telechelic bis(methacrylate) monomer was synthesized and evaluated for its potential use in photopolymerization to yield gel polymer electrolytes (GPEs). The difunctional monomer was obtained via a two-step synthesis by the radical bismonoaddition of telechelic sulfurated dithiol onto allyl alcohol followed by the methacrylation of the resulting diol. It was prepared in 60% overall yield and thoroughly characterized by FTIR, Raman, and NMR spectroscopies. Several photopolymerizable formulations were then proposed by combining telechelic bis(methacrylate) with sodium bis(fluorosulfonyl)imide and tetraethylene glycol dimethyl ether. Upon UV initiation, a series of soft GPE films of various thicknesses were obtained and analyzed by FTIR spectroscopy. Their physicochemical, thermal, and preliminary electrochemical properties were then systematically studied. The resulting GPEs exhibit very low glass transition temperatures (−80 to −40 °C) and high electrical conductivity (1.2 × 10–4 S·cm–1) at room temperature, with electrochemical stability up to 4.5 V vs. Na+/Na. Sodium plating-stripping experiments in Na/GPE/Na symmetric cells show stable polarization voltage curves with no significant fluctuations, indicating homogeneous sodium deposition and dissolution up to a current density of 0.2 mA/cm2. These preliminary and promising results support the potential application of the developed GPEs in sodium batteries
Insights into the role of the covalent Ni–O bonds in LiNiO 2 positive electrodes: a correlative hard X-ray spectroscopy study
No full textInternational audienceThe interest in Ni-rich layered oxide positive electrode materials has been increasing due to their wide applicability particularly in electric vehicles as high capacity and high energy density electrode materials. However, the Ni–O bond array which builds the overall framework and plays a critical role in the charge compensation mechanism of the material requires deeper understanding. This work presents a correlative approach elucidating the role of the local highly covalent Ni–O bonds in a LiNiO2 (LNO) model material. Pristine and electrochemically obtained LNO positive electrodes are analyzed using ex situ X-ray diffraction (XRD) and extended X-ray absorption fine structure (EXAFS) to compare the average and local structural evolution upon Li+ ion de-intercalation. Insights from Ni K-edge X-ray absorption near-edge structure (XANES) and non-resonant Ni Kb X-ray emission spectroscopy (XES) spectra are combined to track the electronic environment of Ni. X-ray Raman scattering (XRS) spectra at the Ni L2,3-edges and O K-edge provide direct bulk electronic information with regard to the interplay between Ni 3d and O 2p states. The overall findings imply that O plays a significant role in the charge compensation process, contributing to the substantial negative charge transfer from the O 2p orbitals, because of the covalency in the Ni–O bonds inside the NiO2 framework within the edge-sharing NiO6 octahedra. The utilization of complementary X-ray spectroscopy techniques clarifies the intricate electronic environment of LNO, which is helpful in understanding Ni-rich positive electrode materials and offering new insights into their covalent nature
Li-Mg alloys as anode for Li batteries in liquid electrolytes: Preparation, shaping, characterization and parametric electrochemical study
No full textInternational audienceLithium-metal batteries offer significant energy density advantages over classical Li-ion technology but their practical implementation is hampered by the poor reversibility of the lithium deposition/stripping processes. To solve this issue, Li-Mg alloys have already been considered as possible alternative and are examined in greater details herein. Homogeneous Li-rich alloys (β-phase) with controlled composition (5–13 at.%Mg) were fabricated and electrochemically reacted with Li to explore the kinetics of the Li-driven β−α phase equilibrium. We showed that the (de)lithiation of the β-phase that occurs at ∼0 Volt vs Li+/Li°, and therefore the most interesting, is strongly limited with the early appearance of Mg-rich α-phase at higher voltages. We demonstrated that this β-domain can be largely extended by using moderate cycling temperature (40 °C), low current density, high initial Li/Mg ratio and rest sequences. Post-cycling observations reveal that repeated (de)alloyings proceed without dendritic growth but rather involve the continuous growth of a porous surface film at the expense of the dense Li-Mg alloy resulting in a sudden drop in capacity when the electrode is becoming completely porous. By limiting the capacity, it is possible to control the progression of this porous layer, improve the efficiency of the Li plating-stripping process, and thus achieve a thousand cycles (0.8 mA.cm-2, 0.8 mAh.cm-2). In full cells, better reversibility is spotted for LiFePO4/Li17Mg compared to LiFePO4/Li cells provided that cycling rate is not pushed over ∼1.2 mAh.cm-2. Overall, we hope these results will provide useful insights for the design of lithium alloy electrodes to improve lithium-metal batteries
Rapid Enantiomeric Ratio Determination of Multiple Amino Acids Using Ion Mobility-Mass Spectrometry
No full textInternational audienceChiral analysis is becoming increasingly important across various scientific fields, including chemistry, pharmaceuticals, biosciences, and more recently, metabolomics. In this context, a high-resolution and high-throughput method was developed for the simultaneous determination of the enantiomeric ratio (er) of seven pairs of amino acid (AA) enantiomers (Arg, Gln, His, Met, Pro, Tyr, and Trp) using flow injection analysis coupled with ion mobility-mass spectrometry (FIA-IM-MS) technology. Specifically, the Single Ion Mobility Monitoring (SIM 2 ) mode on a TIMS-Tof TM instrument enabled the rapid relative quantification of chiral compound mixtures. A linear model accurately described the relationship between enantiomeric ratio and IM-MS response for Arg, Gln, and Pro enantiomers, as evidenced by high R 2 values and unbiased residuals. In contrast, non-linear trends were observed for His, Tyr, and Trp, where a quadratic model significantly improved the fit. However, the linear model was retained for Met, despite an R 2 of about 0.98, due to its comparable performance and simplicity. Measurement accuracy was confirmed with very good recovery rates for er values of 0.95 and 0.99 across all AAs. Finally, the potential of the FIA-SIM 2 -MS approach in chiral analysis was demonstrated, particularly its ability to provide a reliable and efficient high-throughput tool for accurate er determination
Layered Vanadium Phosphates as Electrodes for Electrochemical Capacitors: Part III. Inducing Fast Faradaic Reactions with Cu 2+ Ions in the Interlayer Space
No full textInternational audienceA novel synthesis approach for Cu 0.16 VOPO 4 ·2.5H 2 O material is reported, consisting of VOPO 4 layers incorporating water molecules and Cu 2+ ions within the interlayer space. The inclusion of Cu 2+ ions leads to significant changes in the previously reported electrochemical properties of VOPO 4 ·2H 2 O. Indeed, copper ion insertion leads to a reduced interlayer space, a higher surface area, and, consequently, to a higher specific charge. Moreover, the appearance of new fast faradaic reactions is depicted from the presence of new redox peaks in cyclic voltammograms. The capacity of this material is 93 Cg −1 in 3 M LiOH, 114 Cg −1 in 3 M NaOH, and 126 Cg −1 in 3 M KOH at a scan rate of 5 mVs −1 . It was determined that an intercalation process takes place across the entire operational range in all three electrolytes, even at scan rates as high as 500 mVs −1 . Additionally, electrochemical impedance spectroscopy (EIS) was used for a more comprehensive understanding of the electrochemical role of the interlayer Cu 2+ cations. EIS enables us to propose a new mechanism of electron transfer between VOPO 4 layers and Cu 2+ ion layers, which extends to neighboring layers, thus explaining the fast kinetic of the related faradaic reactions
Effects of co-exposure to benzo-a-pyrene and cerium dioxide nanoparticles on human lung and placental barriers
No full textInternational audienceCerium dioxide nanoparticles (CeO2 NPs) are emerging pollutants widely used for their catalytic properties in diesel fuel and cigarettes. Human exposure to CeO2 NPs rarely occurs in isolation. Benzo-a-pyrene (BaP), a polycyclic aromatic hydrocarbon co-emitted from diesel engines, tends to adsorb onto CeO2 NPs in contaminated environments. To better understand their combined effects on both the lung and placental tissues which arecritical-barriers for the fetus, we coated CeO2 NPs with BaP at two different ratios, mimicking environmental exposure. We characterized the physicochemical properties of BaP-coated NPs in bronchial and placental culture media, assessed coating stability and BaP desorption. We evaluated the biological impact of BaP-coated CeO2 NPs son primary normal human bronchial epithelial cells and purified villous cytotrophoblasts from term human placentas. We compared the response of BaP-coated NPs with that observed under parallel co-exposure, and to individual exposures to BaP and CeO2 NPs. Bronchial cells exhibited toxicity at lower doses under co-exposure by parallel addition compared to BaP-coated NPs. Cytochrome P450 (CYP1A1) induction varied between tissue barriers, exhibiting a BaP dose-dependent response in both tissue models but coating-independent response in trophoblasts, whereas bronchial cells showed a stronger response to BaP adsorbed on CeO₂ NPs. These findings highlight how BaP, when stably associated with CeO2 NPs, exerts modulated effects depending on the tissue,potentially altering its metabolic kinetics and thus its biopersistence. This study underscores the importance ofconsidering particle-bound pollutants when evaluating the health impact of airborne particulate matter, as thismore accurately reflects environmental exposur
Ions at electrochemical interfaces: From explicit to implicit molecular solvent descriptions
No full textInternational audienceWe investigate the interplay between electronic screening inside a metal and screening by a polar molecular solvent, focusing on their impact on the charge induced by an ion and the solvent structure at the interface. To that end, we consider atomistically resolved electrodes within the Thomas–Fermi model of screening and describe the molecular solvent either explicitly via classical molecular dynamics or implicitly using molecular density functional theory (MDFT). In particular, we examine the effect of screening by tuning the Thomas–Fermi screening length lTF, the ion charge by considering Na+ and Cl−, and the solvent nature by studying water and acetonitrile. Consistent with our previous findings without solvent, lTF significantly affects the charge distribution inside the metal. However, lTF has no significant impact on the interfacial solvent structure, suggesting that its effect on the charge distribution induced inside the metal by the ion is essentially due to how the metal responds to the (same) external charge distribution, including the solvent, even though the coupling between both sides of the interface may play a secondary role. Furthermore, MDFT accurately reproduces fine details of the interfacial solvent structure around the ion at a fraction of the computational cost of MD simulations. These results highlight the relevance of MDFT as a powerful tool to model electrochemical systems at the molecular level
Human‐Centered Holographic Assistant using Computer Vision to Interact with Battery Manufacturing Machinery in a Predictive Manner
No full textInternational audienceThis work focuses on a novel human‐centered digital assistant combining Mixed Reality (MR), Computer Vision, and Machine Learning regression to guide professionals and students on how to operate and correctly parameterize battery manufacturing machinery. This article aims to provide a proof of concept of the digital assistant, for a process involving an operator interacting with a semi‐manual electrode calendering machine and examining how the intended calendering parameters will impact the electrode properties after calendering. The operator performs his/her actions while the digital assistant automatically detects the parameters entered by him/her on the machinery. Then, the digital assistant provides real‐time predictions to the operator, helping him/her in decision‐making through a minimalistic holographic interface minimizing visual hindrance. The ergonomics of the solution is optimized by acquiring feedback from users with various experience levels and evaluating their performance. As the necessity for advanced energy storage solutions rises, there is a strong need for modern training and guidance tools that aid in complex battery manufacturing processes at the prototyping stage, involving both semi‐manual and automatic activities. Thanks to MR, the digital assistant has strong potential to improve manufactured electrode and cell qualities by emphasizing the egocentric perspective along the battery cell prototyping process