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Tuning the Diameter of Supramolecular Nanocylinders: Balancing Long and Short Polymer Arms for Optimized Self‐Assembly
No full textInternational audienceNanocylinders find applications in biology, catalysis, and material science due to their high aspect ratio and nanometric diameter, granting them a high specific area. They can be formed by supramolecular assembly in solution of polymers decorated by stickers promoting directional assembly. Controlling the dimensions of nanocylinders impacts their applicative properties. Many strategies exist to tune their length, but much fewer to tune their diameter. We address this point here by synthesizing water‐soluble polymers of different lengths end‐functionalized by hydrogen bonding tris(urea) stickers. It is shown through a combination of light/neutron scattering experiments and cryo‐transmission electron microscopy that short polymer arms (DP ≤ 80) produce thin (d = 10 nm) and long (L > 500 nm) nanocylinders, whereas longer polymer arms (DP ≥ 500), required to significantly increase d, inhibit self‐assembly due to the strong entropic penalty caused by their stretching. A compromise to control d is to mix a few long arms, which increase d, with a sufficient amount of short arms, which alleviate the entropic penalty and maintain high L. This approach proposes a straightforward way to tune the specific area of nanocylinders—a key parameter for applications in catalysis, emulsion stabilization, or interactions with biological materials
From solar cells to solar fuels: assessment of Cu(In,Ga)Se 2 absorbers as photocathode for CO 2 reduction
No full textInternational audienceThis study explores the potential of Cu(In,Ga)Se 2 (CIGS) absorbers, commonly used in high-efficiency solar cells, as photocathodes to improve solar-to-fuel conversion efficiency. CIGS's exceptional light absorption, tunable band gaps, and stability make it an ideal candidate for this application. We examined the performance of bare CIGS and CIGS|CdS pn junctions in photoelectrochemical (PEC) CO 2 reduction, emphasizing the crucial role of interface engineering. Additionally, we assessed the impact of additional ultra-thin functional oxide layers (TiO 2 , NiO, Al 2 O 3 , and SnO 2 ) and inorganic nanostructured co-catalysts (ZnO and Cu 2 O). Our findings reveal that while bare CIGS can reduce CO 2 to CO, the introduction of a pn junction significantly enhances current density and selectivity. A well-optimized photoelectrode based on a CIGS|CdS pn junction can achieve remarkable performance despite its instability, attaining up to 98.5% CO 2 reduction selectivity and photocurrent densities of approximately 8 mA cm -2 at -1.3 V vs SCE under 1-sun illumination. However, protective layers, while improving stability, often led to decreased photocurrent. These insights highlight that combining CIGS absorber layers with appropriate charge transport and catalytic layers is essential for developing efficient and stable PEC systems for CO 2 reduction
Effect of SBPBF₄ addition in acetonitrile- and linear carbonate-based electrolytes: Improving voltage stability and reducing gas evolution in supercapacitors
No full textInternational audienc
O3- vs P2-type Na<sub>x</sub>(Ni,Zn,Mn,Ti)O<sub>2</sub> layered oxides : Comparative study on electrode-electrolyte reactivity and structural stability for cycling performance
No full textSubmitted version of the article before review from the journalInternational audienceSodium layered oxides, having either O3, P2 or P3 stacking, are extensively studied as low-cost cathode materials for high energy Na-ion batteries (NIBs). Previous efforts focused on the optimization of layered oxide compositions resulted in the O3-Na 0.85 Ni 0.38 Zn 0.04 Mn 0.48 Ti 0.1 O 2 and P2-Na 0.67 Ni 0.3 Zn 0.03 Mn 0.52 Ti 0.15 O 2 phases as potential candidates to establish prototype cylindrical 18650 cells with 120-150 Wh/kg specific cell energy. In this study, we focus particularly on the electrode-electrolyte reactivity of these phases, especially at high state of charge (~70% or more) and at high temperatures. Our results indicate that the end-of-charge phase, O1 and O2 formed during complete de-sodiation of O3 and P2, respectively, plays a major role in determining their reactivity. The O1 phase is particularly prone to transition metal migration and oxygen oxidation, having increased reactivity with electrolyte. On the other hand, the P2 layered oxide, while having lower capacity than O3, offers better cycling stability (90% retention after 1000 cycles at 25 °C) due to the greater stability of the O2 end-of-charge structure. These results once again underline the fact that specific capacity should not be the sole metric for determining the most suitable electrode materials for Na-ion or other battery chemistries
Recovery of tantalum from secondary sources by alkaline leachingAdvances in speciation
No full textInternational audienceKeynote for the Ekeberg priz
Recent progress on nonlinear borate single crystals for the design of solid-state laser in the UV range
No full textInternational audienceThe generation of UV light by means of nonlinear optical (NLO) processes from an infrared fundamental beam is indeed a promising path to design all solid-state UV lasers. Such solid-state devices should replace the current excimer lasers and would find many applications (medical surgery, micro photolithography microelectronics etc..). For this purpose, several nonlinear optical crystals must be used, but there are only very few NLO crystals that can achieve the last stage of frequency conversion towards UV, especially when wavelengths below 270 nm are targeted. The presentation will discuss recent progress on NLO borates crystals for solid-state laser conversion in the UV. Two families of crystals with real potential will be particularly discussed: YAl3(BO3)4 (YAB) and Ca5(BO3)3F (CBF) crystals have been developing to compete with the commercial crystals, which are practically used today for UV conversion (LBO, BBO or CsLiB6O10 (CLBO)).Crystal growth and nonlinear optical properties of the two NLO borate families: Ca5(BO3)3F (CBF) and YAl3(BO3)4 (YAB) will be presented. Single crystals of (CBF), can be grown by the flux method [1-3]. These borate compounds were investigated for nonlinear optical applications and were expected to exhibit an extended transparency window in the ultraviolet. CBF crystal allows the generation of UV from birefringent Phase matching Type II-THG of near IR fundamental wavelengths.The borate YAB remains the only one non hygroscopic crystal allowing second harmonic generation of 532 nm solid state laser. YAB crystals grown allows top seeded solution growth (TSSG) method with La2O3-B2O3-LiF as a flux. Both CBF and YAB crystal allow frequency conversion of solid-state laser in the UV range that will be discussed [4-5].References1.G. Chen, Y. Wu, P. Fu, J. Cryst. Growth 292, 449 (2006). https://doi.org/10.1016/j.jcrysgro.2006.04.079 2.K. Xu, P. Loiseau, G. Aka, J. Lejay, Crystal Growth and Design 9(7), 3137 (2009)-https://doi.org/10.1021/cg800958u 3.K. Xu, P. Loiseau, G. Aka, R. Maillard, A. Maillard, T. Taira, Optics Express 16(22), 17735 (2008).4.L. Deyra, S.Ilas, X. Délen, P. Loiseau, F. Balembois, G. Aka, F. Salin, P Georges, Optics Mat. Express 3 (11) 1798. (2013). https://doi.org/10.1364/OME.3.00179
Exploring ALD-SnO₂ Coatings on Stainless Steel as an Alternative to Titanium for PEM Electrolyzer Bipolar Plates
No full textInternational audienceProton exchange membrane (PEM) electrolysis is a promising technology for producing low-carbon hydrogen via water splitting. Currently, the electrolyzer stack represents the main contributor to system capital costs [1]. It is largely due to the use of bare titanium for bipolar plates, which offers high corrosion resistance in acidic and high-voltage environments. However, titanium has notable drawbacks: it is expensive, and its passive oxide layer gradually grows during operation, increasing ohmic resistance and causing a progressive decline in performance [1]. One attractive strategy to overcome these limitations is the application of protective and conductive coatings on low-cost substrates, combining durability and electrical conductivity with reduced material costs.Stainless steel coated with tin oxide via atomic layer deposition (ALD-SnO₂) has emerged as a promising, cost-effective alternative to titanium for PEM electrolyzer bipolar plates. The growth of ALD-SnO₂ has been systematically studied by varying substrate surface finish, reagents chemistry, number of deposition cycles, and deposition temperature. Corrosion resistance was evaluated by chronoamperometry at 2,0 V vs. NHE in H₂SO₄ pH 3, while electrical conductivity performance was assessed through interfacial contact resistance (ICR) and four-point probe resistivity measurements. ALD-SnO₂ coated stainless steel showed good corrosion resistance in short term tests with no dependence on deposition parameters. The ICR results highlight the effect of the substrate surface finish, lower values are obtained for higher surface roughness. Also, a dependance on temperature of deposition for the electrical resistivity is observed. Moreover, ellipsometry and quartz crystal microbalance measurements revealed substrate-assisted growth during the initial ALD cycles, leading to two distinct zones in the final coating. These zones were characterized by X-ray photoelectron spectroscopy, transmission electron microscopy and electrochemical impedance spectroscopy, with particular attention to the interface with the stainless-steel substrate. This study confirms the potential of ALD-SnO₂ coated stainless steel as a durable, high-performance, and cost-effective alternative to titanium for PEM electrolyzer bipolar plates. The crucial role of deposition parameters in controlling the coating functional properties was also points out.[1] M. Carmo et al., Int. J. Hydrog. Energy, 2013, 38(12):4901-4934, https://doi.org/10.1016/j.ijhydene.2013.01.15
Probing the structural and electronic heterogeneity of LiVPO4F and KVPO4F positive electrode materials by combined X-ray absorption and emission spectroscopy
No full textInternational audienceVanadium fluoride phosphates are highly intriguing due to their diverse crystal structures, which significantly influence their electrochemical properties, making them favorable candidates for Li-ion and post Li-ion battery applications. In this study, high-energy resolution fluorescence-detected X-ray absorption near-edge structure (HERFD-XANES) spectroscopy and X-ray emission spectroscopy (XES) are combined to describe and understand the distinctive features of Tavorite-type LiVPO4F and KTP-type KVPO4F, along with their deintercalated homeotypic phases. The HERFD-XANES spectra, featuring the 1s2p resonant inelastic X-ray scattering (RIXS) process at the pre-edge region, provide detailed information on the local structure, while a thorough interpretation of the XES signals, including Core-to-Core (CtC) Kα and CtC Kβ, offers complementary information about local structures and oxidation states, respectively. Furthermore, the occupied and unoccupied electronic states close to the Fermi level are described by combining the information from the XES Valence-to-Core (VtC) Kβ2,5 emission line and the HERFD-XANES pre-edge, respectively. The thorough understanding of these spectral signatures is made possible by the application of ab initio calculations. Overall, this comprehensive analysis of both local geometric and electronic structures provides valuable insights into these materials with distinct crystal structures which are applied as alkali ion positive electrodes
Ion Mobility Mass Spectrometry to Probe Sequences in Supramolecular Copolymers
No full textInternational audienceThe analysis of the microstructure of supramolecular copolymers is difficult because of their dynamic character. Here, benzene‐1,3,5‐tricarboxamide (BTA) co‐assemblies are analysed by ion mobility ‐ mass spectrometry (IM‐MS) to reveal the presence of various sequences. For example, the IM‐MS mobilogram for hexamers composed of 4 units from a first monomer and 2 units from a second monomer is a broad distribution due to the presence of 9 possible isomeric sequences, which can be sorted out based on calculated collision cross‐sections. This approach gives unprecedented information on supramolecular copolymer sequences
Synthesis and Biological Evaluation of a New Biphenyl-Based Organogold(III) Complex with In Vitro and In Vivo Anticancer Activity
No full textInternational audienceDespite recent advances in cancer treatment, there is still a need for novel compounds with antineoplastic activity. Among, 11 biphenyl-based organogold(III) N-heterocyclic carbene (BGC) complexes of the general formula [(C^C)Au(NHC-pyr)X], where (C^C) = 4,4'-diterbutylbiphenyl, X = Cl or phenylacetylide, and (NHC-pyr) is a pyridyl-substituted NHC ligand, the complex BGC4 bearing a 4-CF3-pyridyl substituent and a chloride ligand showed promising antineoplastic activity on the triple negative breast cancer cell line. BGC4 was able to induce cell apoptosis but had no effect on the cell cycle. In vivo, BGC4 reduced the tumor growth rate by increasing the necrosis area and decreasing the mitotic activity. Repeated injections of BGC4 did not induce common side effects. The present investigation shows that BGC4 is a promising antineoplastic candidate. Its potential as a future chemotherapy for the treatment of cancer will be strengthened by evaluating its efficacy in combined treatment with current chemotherapy