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Mitigation of Defect Formation at the NiO x /Perovskite Interface in p-i-n Perovskite Solar Cells
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Tailoring Oxide/MAX Phase Nanocomposites via Low‐Temperature Oxidation for Lithium‐Ion Battery Anodes: Peeking Behind the Electrochemical Mechanism via In Situ Investigations
No full textInternational audienceAbstract This study explores the potential of MAX phase/oxide nanocomposites as negative electrodes for lithium‐ion batteries. The main objective is to enhance the stability and performance of tin oxide‐based electrodes by reducing volume changes upon cycling. The approach involves the synthesis of a Sn‐containing MAX phase (Ti 3 Al 0.3 Sn 0.7 C 2 ) followed by oxidation at different temperatures (600, 700, and 850 °C). Comprehensive characterization reveals that partial oxidation produces nanocomposites containing titanium and tin oxide nanoparticles with different compositions depending on the annealing temperature. The residual presence of the MAX phase contributes to the stability of the electrode, buffering volume changes during cycling. The sample oxidized at 700 °C exhibits the best trade‐off between specific capacity (350 mAh g −1 at 50 mA g −1 ) and reversibility (99.2% Coulombic efficiency), and it delivers a reversible specific capacity of 133 mAh g −1 at 2000 mA g −1 which is superior to the high‐rate performance typically reported for graphite. In situ studies provide insights into the mechanism of (de)lithiation, confirming the reduction of Sn(IV) to metallic Sn and the subsequent formation of Li‐Sn alloys, while the residual MAX remains electrochemically inactive, preserving structural integrity and transport properties
Bromine-rich argyrodites compositions: Enhancing lithium-ion conductivity for improved solid-state battery performance
No full textInternational audienceHalide-enriched lithium argyrodite superionic conductors are considered as promising candidates for all-solid-state batteries due to their soft structure and high ionic conductivity. Challenges remain, including chemical instability and incompatibility with anode materials, and in addition a deeper understanding of the fundamental aspects of ionic transport and performance is required. In this study, we investigated two argyrodite mixed-halide series of compositions, Li6−xPS5−xBrClx and Li5.5PS4.5Br1.5−xClx. By employing a range of techniques including X-ray diffraction (XRD), neutron diffraction, nuclear magnetic resonance (NMR) spectroscopy, electrochemical impedance spectroscopy and machine learning based molecular dynamics, we found that increasing the halide substitution enhances ionic conductivity. Notably, the Li5.4PS4.4BrCl0.6 composition achieves an ionic conductivity of 10 mS/cm, demonstrates superior air stability compared to conventional lithium argyrodites and allows for the fabrication of well-performing all solid-state batteries. Our results reveal that in lithium-poor compositions the lithium environments in the 4a and 4d cages become more alike, facilitating fast long-range lithium-ion transport. This work paves the way for the development of air-stable, high-conductivity sulfide electrolytes, advancing the practical implementation of solid-state batteries
Non-linear elastic-plastic behavior of the invert glass lithium phosphorous oxynitride (LiPON)
No full textInternational audienceMicro and nano-scale mechanical behavior of network/ionic glasses is dictated by their composition and the number of constraints per structural unit. From this perspective, the glass LiPON presents the opportunity for enhancement of the microscale ductility due to its rather unconstrained orthophosphate structure. We use instrumented nanoindentation with different tip geometries to investigate the mechanical response of LiPON glass. The results reveal that the elastic modulus of LiPON is not constant and depends on pressure. With the method utilizing spherical nanoindentation and continuous stiffness measurement (CSM) we determine the yield point of LiPON. We propose the Drucker-Prager type of yield criterion for LiPON and estimate its yield stress in compression as 2.4 GPa. There exists another stress threshold, however, around 490 MPa, at which the elastic deformation becomes non-linear, and this can be mistaken for the yield stress
Photocatalytic Recovery of Noble Metals by Covalent Silyl Polyoxophosphotungstate–Porphyrin Copolymers
No full textInternational audienceThe photocatalytic recovery of noble metals on photosensitive semiconductors such as TiO2 is well-established for forming M/TiO2 but has notable drawbacks. TiO2 suffers from low conversion efficiency due to significant recombination of photogenerated electron–hole pairs. Its wide energy band gap (3.2 eV) also restricts excitation to high-energy UV light, limiting its use with solar energy. This study proposes an efficient alternative using hybrid polyoxometalate (POM)–porphyrin copolymers for the photocatalytic recovery of Ag and Pt under visible light. Copolymeric films composed of hybrid polyoxometalates and porphyrins have been obtained by the electrooxidation of 5,15-(di-p-tolyl)porphyrin (H2T2P) or 2,3,7,8,12,13,17,18-octaethylporphine zinc(II) (ZnOEP) together with Keggin or Wells–Dawson-type organosilyl polyoxophosphotungstate ([PW11Si2O40C26H16N2]TBA3 or [P2W17Si2O62C26H16N2]TBA6). In these films, porphyrin subunits can be excited under visible illumination, acting as photosensitizers that transfer electrons to the polyoxometalate catalysts. Notably, POM–porphyrin films demonstrated high efficiency in Pt(IV) photoreduction over repeated cycles without catalyst degradation
3D Electron diffraction on nanoparticles: minimal size and associated dynamical effects
No full textInternational audienceOver the past decade, advances in electron diffraction (ED) have significantly improved the determination and refinement of crystal structures, making it a viable alternative to traditional X-ray diffraction (XRD), especially for very small volumes, such as nanoparticles (NPs). This work evaluates the application of advanced 3D ED techniques to the analysis of isolated NPs, focusing on their efficacy and limitations in terms of crystal size and accuracy of results. Our investigation begins by addressing the challenges of obtaining 3D ED data for NPs, including sample preparation, instrument capabilities, and the choice of 3D ED methods. We find that 3D ED can provide highly accurate structure refinements for crystals in the 50-100 nm range and is also effective for the analysis of NPs as small as 10 nm. While kinematical approximations often provide accurate refinements similar to those obtained from powder XRD, the accuracy depends on the specific data set and may not always align with traditional reliability indicators.Our study shows that dynamical scattering effects, even in tiny crystals, challenge the assumption that they are negligible in thin crystal scenarios. Addressing these effects through full dynamical refinement significantly improves the accuracy and reliability of the structure determination. This report suggests a paradigm shift in viewing dynamic scattering effects not as mere obstacles but as opportunities to explore crystal structures in greater detail on smaller scales. By embracing these complexities, 3D ED can provide precise and reliable structural insights that are critical to the advancement of nanotechnology and materials science
Panchromatic Gold Alkynyl Complexes with Pyrenyl<i>‐N</i>‐Heterocyclic Carbene Ligand Displaying Anti‐Kasha Behavior
No full textInternational audienceA unique family of alkynyl-gold(I)-complexes (1-6) containing pyrenyl-NHC chromophoric ligand (NHC = Nheterocyclic carbene) has been prepared and fully characterized. The complexes were engineered such that a pyrenyl ligand was introduced to one nitrogen center of the carbene unit while to the other nitrogen center we attached a methyl (1), n-butyl (2), or naphthyl (3-6) group in order to probe their effect on the photophysical properties of our Au-alkynyl complexes. For comparison purposes the cyanide-gold(I) complex ( 7) was prepared and fully characterized. The molecular structures of 3 and 4 and 7 were ascertained by X-ray diffraction study. In stark contrast to the alkynyl complexes, the cyano-Au complex 7 displayed only weak fluorescence highlighting the impact of the -C≡C─Ar unit on their emission properties. The alkynyl complexes displayed different behavior, for instance, complex 1 exhibited excimer emissions originated from the pyrene chromophore while compound 2-6 displayed remarkable multi-emissive properties, mainly 3-6 showing panchromatic behavior with emissions dependent on the excitation wavelengths suggesting anti-Kasha behavior. TD-DFT-calculations were carried out to support interpretation of the experimental results. These remarkable results have not been observed previously, making these molecules important candidates for a wide range of applications in the optical domain.</div
Mannich Reaction of Secondary Benzylzinc Reagents: Synthesis of α,β‐Disubstituted β‐Arylethylamines
No full textInternational audienceThe organometallic multicomponent Manich reaction of secondary benzylzinc compounds is described. These organometallic reagents were efficiently prepared by direct metalation of (1-bromoethyl)benzenes in tetrahydrofuran with zinc dust. Their subsequent multicomponent Mannich coupling with amines and aldehydes allowed the straightforward preparation of a large variety of α,β-disubstituted β-arylethylamines in yields ranging from 13% to 79%. This reaction was found to require the use of a heated mixture of tetrahydrofuran and acetonitrile, tetrahydrofuran being essential to reach good yields and acetonitrile ensuring reproducibility
Evolution, structure and function of L-cysteine desulfidase, an enzyme involved in sulfur metabolism in the methanogenic archeon Methanococcus maripaludis
No full textInternational audienceThe biosynthesis of sulfur-containing molecules, which play essential roles in cell metabolism, often relies on enzymes that mobilize sulfur from cysteine. The function of such enzyme, L-cysteine desulfidase CyuA, which catalyzes L-cysteine decomposition to pyruvate, ammonia, and hydrogen sulfide, remains incompletely understood. Here, we used phylogenetic, genetic, biochemical, spectroscopic, and structural approaches to connect molecular structure to cellular physiology and evolutionary history and elucidate CyuA’s role in sulfur metabolism. We found that Methanococcales and several other archaeal lineages acquired CyuA via horizontal gene transfer from bacteria. In Methanococcus maripaludis , CyuA (MmCyuA) stimulates growth in sulfide-rich conditions and enables slow growth with cysteine as the sole sulfur source. Crystallographic and biochemical data reveal that MmCyuA binds a [4Fe-4S] cluster coordinated by three conserved cysteines; the fourth ligand is a nonconserved cysteine in the wild-type enzyme but is replaced by glycerol or ethylene glycol in a variant. These results enabled modeling of the enzyme–substrate complex, allowing us to propose a detailed mechanism for L-cysteine desulfuration by CyuA, potentially involving a transient [4Fe-5S] species to transfer sulfur from cysteine to various [4Fe-4S]-dependent tRNA sulfuration enzymes. These findings advance understanding of sulfur activation and trafficking related to biosynthetic pathways leading to sulfur-containing compounds
Immobilizing Lead and Healing Surface Defects via Perfluorinated Tertiary Amine Molecules Enables High‐Performance Sustainable Inverted Perovskite Solar Cells
No full textInternational audienceAbstract The intrinsic instability and nonradiative recombination induced by surface defects hinder the further development of p‐i‐n inverted perovskite solar cells (PSCs). Simultaneously, the commercial application of inverted PSCs is limited by environmental unfriendliness resulting from lead leakage. Herein, a universal perfluorination strategy is reported to immobilize lead and passivate surface defects of perovskite films in inverted PSCs. It is demonstrated that perfluorinated perfluorotriethylamine (PFTEA) can form PFTEA·PbI 2 complex with PbI 2 via a strong coordination bond, which is favorable for suppressing lead leakage and promoting defect passivation. Due to much reduced surface nonradiative recombination, the PFTEA‐modulated inverted PSCs deliver a fascinating certified stabilized power conversion efficiency (PCE) of 26.65%, a record efficiency value reported for PSCs using the vacuum flash evaporation technique. Moreover, the PFTEA‐modulated devices maintain 92% of their initial PCE after 1000 h of continuous maximum power point tracking. This work provides a simple and effective avenue to advance the sustainable development of inverted photovoltaic technology through a perfluorination strategy