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Élucidation de la dynamique des porteurs et de l’ingénierie des interfaces dans le Sb₂S₃ : Vers une photoanode efficace pour l’oxydation de l’eau
No full textInternational audienceConjugation of low‐cost and high‐performance semiconductors is essential in solar‐driven photoelectrochemical (PEC) energy conversion. Sb2S3 is a wide‐bandgap (≈1.7 eV) semiconductor with the potential to deliver a maximum photocurrent density of 24.5 mA cm−2, making it highly attractive for PEC water splitting applications. However, bulk Sb2S3 exhibits intrinsic recombination issues and low electron–hole separation, posing a limit to photocurrent generation. This study clarifies the carrier dynamics by ultrafast spectroscopy measurements and proposes the design of a heterojunction between Sb2S3 and SnO2, with suitable band‐edge energy offset. The SnO2/Sb2S3 heterojunction enhances the charge separation efficiency, resulting in improvement of the photocurrent. The SnO2/Sb2S3 photoanode, fabricated entirely by vapor deposition processes, demonstrates photoelectrochemical water oxidation with a photocurrent density up to ≈3 mA cm−2 at 1.38 V versus RHE.</p
opXRD: Open Experimental Powder X-Ray Diffraction Database
No full textInternational audiencePowder X-ray diffraction (pXRD) experiments are a cornerstone for materials structure characterization. Despite their widespread application, analyzing pXRD diffractograms still presents a significant challenge to automation and a bottleneck in high-throughput discovery in self-driving labs. Machine learning promises to resolve this bottleneck by enabling automated powder diffraction analysis. A notable difficulty in applying machine learning to this domain is the lack of sufficiently sized experimental datasets, which has constrained researchers to train primarily on simulated data. However, models trained on simulated pXRD patterns showed limited generalization to experimental patterns, particularly for low-quality experimental patterns with high noise levels and elevated backgrounds. With the Open Experimental Powder X-ray Diffraction Database (opXRD), we provide an openly available and easily accessible dataset of labeled and unlabeled experimental powder diffractograms. Labeled opXRD data can be used to evaluate the performance of models on experimental data and unlabeled opXRD data can help improve the performance of models on experimental data, for example, through transfer learning methods. We collected 92,552 diffractograms, 2179 of them labeled, from a wide spectrum of material classes. We hope this ongoing effort can guide machine learning research toward fully automated analysis of pXRD data and thus enable future self-driving materials labs
Mechanistic insights on hydrazones synthesis: a combined theoretical and experimental study
No full textInternational audienceHydrazone derivatives of isoniazid have demonstrated potential as anti-tubercular agents. While previous studies have predominantly focused on their biological activity, existing literature lacks both experimental and computational studies on the mechanisms and kinetics of their syntheses. This study aims to address this gap by employing a combined computational and experimental approach to investigate the hydrazone synthesis from isoniazid and isophthalaldehyde through competitive-consecutive reactions. Density functional theory (DFT) calculations were performed to explore the possible reaction pathways and their energy profiles in both the gas phase, and with solvation. Experimental kinetic studies were conducted in a jacketed batch reactor using ethanol/water and dry acetonitrile to support the computational findings by assessing the impact of solvents on reaction dynamics. The computational results indicate that water has a catalytic effect on the reaction, not only by assisting in the rate-limiting step but also by avoiding high-energy isomerizations, required in its absence. Experimental kinetics in dry acetonitrile demonstrated a very slow reaction rate, while the ethanol/water system achieved higher conversion rates in the same amount of time, aligning with the computational findings. Experimentally determined activation energies closely matched the value predicted computationally
Partially fluorinated derivatives as a powerful tool for the restoration of blanched easel paintings
No full textInternational audienceThe use of specific coatings has considerable importance in the field of cultural heritage conservation. The blanching of easel paintings is a worrying phenomenon induced by excessive humidity and porous structures, often obscuring the image beneath a white haze. The research available in the literature describing solutions to solve this problem is extremely limited. In this research, new oligoamides containing hydroxyl and/or amino groups, i.e., partially fluorinated oligodiethylene succinamide-L-tartaramide (DSTF) and oligodiethylene succinamide (DSF), were designed to give high affinity with the polar components present in paint films through noncovalent interactions, and have reduced environmental impact compared to the previously proposed perfluoroamide (DC6G900). These innovative products represent one of the few solutions proposed for this area of application. Their syntheses were carried out via condensation and subsequently ring-opening reaction of the short-fluorinated epoxy compound, 3-perfluorohexyl-1,2-epoxypropane (EC6F). The short-fluorinated chain has a dual effect; it improves surface performance by lowering surface tension while simultaneously reducing environmental impact compared to the perfluoro source previously used. The performance of the two new fluorinated oligoamides (DSTF, DSF) on blanched easel paintings was investigated through a series of tests, from the macroscopic to the microscopic scale. The new fluorinated oligoamides dramatically decreased the luminance value (almost restoring the value of the un-blanched sample) in comparison with the other tested compounds (ESTF, ESF, DF and DC6G900 as a reference). This result is ascribed to the ability of the compounds to fill the pores of the blanched surfaces, as demonstrated by the morphological study using a Field emission gun -Scanning electron microscopy. In addition, preliminary investigations showed that all the tested compounds, can be removed from the treated mock-ups using 2-propanol or 2,2,2-trifluoroethanol, giving promising results concerning the removal of the restoration treatments
Niobium Bronzoids as Negative Electrodes: Synthesis, Structure, and Electrochemical Properties of Li 2 Nb 4 P 2 O 16 and Na 2 Nb 4 P 2 O 16
No full textInternational audienceIn this study, sodium- and lithium-based phosphate niobium bronzes and bronzoids with the general formula Ax(PO2)2(NbO3)m (where A = Na/Li and m = 4), specifically Na2Nb4P2O16 and Li2Nb4P2O16, are investigated. The crystal structure of Na2Nb4P2O16 is revisited using a combination of laboratory and synchrotron powder X-ray powder diffraction. It is found to crystallize in the P21/a space group (different from the previously reported P21 space group), with lattice parameters a = 13.2503 (6) Å, b = 5.3498 (2) Å, c = 19.0807 (7) Å, β = 109.9574 ° (3) and V/Z = 317.833 (9) Å3. Additionally, we synthesized and determined the crystal structure of Li2Nb4P2O16 for the first time, introducing it as a lithium-based phosphate niobium bronzoid. It crystallizes in the Pc21n orthorhombic cell with lattice constants a = 6.7031 (4) Å, b = 5.1936 (2) Å, c = 17.4260 (8) Å, and V/Z = 303.324 (5) Å3. As negative electrodes in Li batteries, Li2Nb4P2O16 and Na2Nb4P2O16 exhibited average discharge capacities of 386 and 277 mAh/g, respectively, at C/15 in a voltage window of 3.0-0.1 V
Effect of Gold Substrate on the Interface between Graphene Monolayer and an Ionic Liquid
No full textInternational audienceThe unique properties of graphene make it an ideal material for electrochemical studies, particularly of the electrochemical double-layer. However, experimental studies generally require depositing graphene on substrates like gold, that may affect the electronic structure of the electrode and thus the ions adsorption properties. This study explores the impact of gold substrates on graphene electrochemical behavior using molecular dynamics. Two systems were compared: graphene on gold (Gr@ Au) and standalone graphene (Gr), with ionic liquid ([EMIM]-[TFSI]) as the electrolyte. The model accounts for the different metallic behavior of graphene and gold under the various applied potentials. Despite a similar electrolyte structure, the interfacial capacitance is affected, which can be attributed to different charge distributions within the electrode. The variations of the van der Waals and Coulomb energies also show some differences in the presence of gold, in particular for low potentials
Investigation of crystallites in CVD diamond films and their impact on stress distribution
No full textInternational audienceDiamond is potentially the best candidate for many applications in electronics, quantum technologies, optics, mechanics, thermal management, or biomedical field, owing to its uniquecombination of physical and chemical properties. Nevertheless, it requires the production of very high quality diamond layers which can be limited crystallites. Indeed, these microstructures having different morphologies and orientations, they disrupt diamond growth uniformity andgenerate localized stress fields that degrade diamond properties [1]. Understanding the morphology and stress propagation associated with crystallites is thus essential forimproving the quality of CVD diamond. It is the main purpose of this study which focuses on the characterization of crystallite morphology and related stress fields. By varying growth parameters like CH4/H2 ratios,nitrogen concentrations, and growth temperatures, the conditions affecting the formation of crystallites will be identified and the direct impact stress distribution and overall film quality will be evaluated. In this aim, different samples will be prepared by laser cutting and polishing after growth in orderto obtain cross-sections with smooth surfaces suitable for the characterization of crystallites and the visualization of stresses propagation by birefringence as illustrated in Figure 1. Scanning Electron Microscopy (SEM) will be also performed to analyze the size, shape, and spatial distribution of crystallites. Raman spectroscopy will be used to map the local stress fields around crystallites and determine zones of tensile or compressive stress [2]. Additionally, photoluminescence (PL) will be carried out to assess preliminary effects on nitrogen-vacancy (NV) centers formation. These findings will provide a base-level understanding of crystallite-induced stress and its implication on diamond quality. This work will allow identifying growth conditions that promote orinhibit crystallite formation and developing strategies to minimize their impact on stress propagation, thus enabling the production of "quantum-grade" CVD diamond films. References 1. Ren, Y et al. Materials 2024, 17, 13112. Yukako Kato, Hitoshi Umezawa, Shin-ichi Shikata, Tokuyuki Teraji. Diamond and Related Materials,Volume 23,2012,Pages 109-111
Stability and Mitochondrial Localization of a Highly Cytotoxic Organogold(III) Complex with Diphosphine Ancillary Ligand in Lung Cancer Cells
No full textInternational audienceWe present a comprehensive study on the chemical reactivity in gas phase, with amino acids and peptides and in cell, the anticancer activity and localization of a series of seven cationic biphenyl gold(III) complexes with aryl, alkyl and chiral diphosphine ancillary ligands. Despite some structural differences, all the complexes similarly featured high stability toward reduction or ligand exchange in cell‐free conditions. The biphenyl Au(III) complex including the 1,2‐diphenylphosphinoethane (dppe) ligand manifested the same high stability in cellular setting, as attested by a combination of cryo‐Synchrotron Radiation‐X‐Ray Fluorescence (cryo‐SR‐XRF) nano‐imaging and cryo‐Synchrotron Radiation‐X‐ray Absorption Spectroscopy (cryo‐SR‐XAS) measurements. Tandem cryo‐SR‐XRF elemental mapping and confocal fluorescence microscopy demonstrated the selective accumulation of the dppe complex in mitochondria. This represents the first study of the speciation and distribution of an organogold(III) complex in cancer cells
Understanding and Enhancing the Cycling Stability of Layered Double Hydroxides with Intercalated Ferrocene Anions for Energy Storage Application
No full textInternational audienceIn this work, the layered double hydroxide (LDH) Mg 2 Al(OH) 6 was intercalated with redox active ferrocene carboxylate anions in order to implement charge storage capability to the interlayer spaces of the LDH structure. Two sets of anions, namely mono‐ and dicarboxylic ferrocene, were intercalated to produce two different active materials: MgAl‐FcMono and MgAl‐FcDi. The electrochemical investigation of these two materials was performed in two model electrolytes: 1 M LiTFSI in H 2 O and Pyr 13 TFSI. In the aqueous electrolyte, the first charge reaches the full theoretic capacity of ca. 60 and 40 mAh g −1 for both materials. However, significantly less capacity is stored and delivered during subsequent cycles. In‐situ UV/vis experiments identified the loss as a release of charged ferrocene anions from the LDH during oxidation in the charging process, which is more severe for MgAl‐FcMono. It is possible to prevent this release of redox species by the use of the ionic liquid Pyr 13 TFSI as a high concentrated electrolyte. Subsequently, both materials cycled very steadily with high coulombic efficiency for 150 cycles. This better understanding of the capacity degradation of the LDH‐ferrocene active material is key to improving this new and promising concept of using modified LDHs as active material in energy storage application
Hybrid CIGS‐Cobalt Quaterpyridine Photocathode with Backside Illumination: a New Paradigm for Solar Fuel Production
No full textInternational audienceChalcogenide‐based thin‐film solar cell optimized for rear illumination and used for CO2 reduction is presented. Central to this innovation is a thinner, Cu(In,Ga)S2 chalcopyrite absorber coated with a robust metallic top layer, which potentially surpasses the performance of conventional front‐illuminated designs. Using cobalt quaterpyridine molecular catalyst, photocurrent densities for CO2 reduction exceeding 10 mA/cm2 at 0.0 V vs. RHE under 1 Sun illumination, and ca. 16 mA/cm2 at ‐0.25 V vs. RHE were achieved in voltammetry experiments. Controlled potential electrolysis showed catalytic activity over 20 h with selectivity for CO ranging from > 92% (first 4 hours) to 86% at the end of the experiment. This approach opens limitless possibilities for employing various reduction catalysts, extending far beyond CO2 reduction. It imposes minimal constraints on absorption properties, immobilization methods, and catalyst nature, setting the stage for high‐performance, adaptable PEC devices