Portail HAL ENSCP
Not a member yet
9647 research outputs found
Sort by
Swelling and evaporation determine surface morphology of grafted hydrogel thin films
No full textInternational audienceWe experimentally study the formation of surface patterns in grafted hydrogel films of nanometer-to-micrometer thicknesses during imbibition-driven swelling followed by evaporation- driven shrinking. Creases are known to form at the hydrogel surface during swelling; the wavelength of the creasing pattern is proportional to the initial thickness of the hydrogel film with a logarithmic correction that depends on microscopic properties of the hydrogel. We find that, although the characteristic wavelength of the pattern is determined during swelling, the surface morphology can be significantly influenced by evaporation-induced shrinking. We observe that the elastocapillary length based on swollen mechanical properties gives a threshold thickness for a surface pattern formation, and consequently an important change in morphology
Characterization of Coated Materials for Bipolar Plates in Proton Exchange Membrane Water Electrolyzers by Electrochemical Impedance Spectroscopy
No full textInternational audienceProton exchange membrane (PEM) electrolysis is a promising solution to produce low-carbon hydrogen by water splitting. Currently, stacks are the main cost driver of PEM electrolyzers’ system capital costs [1]. It is mainly explained by the use of bare titanium for the bipolar plates, because of its high corrosion resistance in acidic environment at high voltage. Nevertheless, one drawback of titanium (in addition of its high price) is the growing of its passive oxide layer during operation, which increases ohmic resistance and reduces electrolyzer performance over time [1]. Therefore, one promising approach to replace bare titanium is the use of coatings on low cost substrate. Stainless steel coated by metal oxide made by atomic layer deposition (ALD-MOx) with variation of the deposition parameters (chemistry of reagents, number of cycles and temperature of deposition) were studied by electrochemical impedance spectroscopy (EIS) to investigate their physical and chemical properties (oxide thickness, electrical resistivity, corrosion resistance…) in H2SO4 pH 3 electrolyte. EIS measurements were carried out on bare stainless steel, ALD-MOx coated conductive glass (ITO) and ALD-MOx coated stainless steel. This enabled to investigate the Cr2O3 native oxide of bare stainless steel and ALD-MOx separately, as well as their combination. Measurements at rest potential revealed a non-ideal capacitive behavior (corresponding to a constant phase element) for the different oxides. Various electrical equivalent circuits were compared to fit the experimental data, taking into account various parameters and describing different physico-chemical phenomena (presence of an electrical double layer, influence of the Cr2O3/ALD-MOx interface…). Based on these circuits, different time constant distribution models (surface and normal distribution [2]) were taken into account to calculate the effective capacitance and the oxide thickness (Cr2O3 and ALD-MOx). Comparing the oxide thicknesses calculated from EIS data with those measured by ellipsometry provides a means of validation or refutation of the various assumptions made for fittings and calculations, and contributes to the understanding of the system. Among the time constant distribution models, the Power-Law model [3] was used to characterize the electrical resistivity profile in the oxide coatings. That revealed the improvements brought by the ALD-MOx coatings on the electrical properties of the stainless steel surface. This has been confirmed by resistivity measurements made with the 4-point probe method. It has also been revealed that the native Cr2O3 film has a significant impact on the global electrical performances of ALD-MOx coated stainless steel, underlining the importance of surface preparation before deposition.[1] M. Carmo et al., Int. J. Hydrog. Energy, 2013, 38(12):4901-4934, https://doi.org/10.1016/j.ijhydene.2013.01.151[2] M. Orazem et al., J. Electrochem. Soc., 2013, 160(6):C215-C225, https://doi.org/10.1149/2.033306jes[3] B. Hirschorn et al., J. Electrochem. Soc., 2010, 157(12):C452-C457, https://doi.org/10.1149/1.349956
Structure-activity relationships in catalysts with advanced solid-state NMR of quadrupolar nuclei
No full textInternational audienc
Assessing ultrasonic and optical flow velocimetry in a millifluidic device using oil-in-water emulsions as blood mimicking fluid
No full textInternational audienceBlood-mimicking fluids (BMFs) play a critical role in ultrasonic imaging and Doppler flow studies by replicating the physical and acoustic properties of blood. This study introduces a novel soybean oil-in-water emulsion as a BMF with particle size and deformability akin to red blood cells. Using a millifluidic device, we cross-validated flow profiles through both Doppler velocimetry and optical particle tracking, demonstrating compatibility with theoretical Poiseuille flow models. The millifluidic 1 chip, fabricated via stereolithography, provided an optimized platform for dual optical and ultrasonic assessments. Results showed strong agreement between the two methods across a range of flow rates, affirming the suitability of the emulsion for velocimetry applications. Furthermore, the acoustic properties of soybean oil droplets support their potential as an echogenic and stable alternative to conventional BMFs
Mechanism and Optimization of Ruthenium-Catalyzed Oxalamide Synthesis Using DFT
No full textInternational audienceThe oxalamide skeleton is a common structural motif in many biologically active molecules. These scaffolds can be synthesized via ruthenium pincer complex-catalyzed acceptorless dehydrogenative coupling of ethylene glycol and amines. In this study, we elucidate the mechanism of this oxalamide synthesis using density functional theory calculations. The rate-determining state is identified as the formation of molecular hydrogen following the oxidation of hydroxyacetamide to oxoacetamide. In predictive catalysis exercises, various modifications to the ruthenium pincer catalyst were investigated to assess their impact on the reactivity
Pressure-induced stabilization of 3D hyperhoneycomb Li2(Sn1–xRux)O3
No full textInternational audienceMetal-ordered rock-salt oxides (e.g., AMO2, A2MO3, A3MO4) exhibit diverse functionalities arising from cation ordering, yet their structural evolution is difficult to predict due to the lack of systematic design principles. For A2MO3 compounds, although two-dimensional (2D) honeycomb structures have been widely explored, the three-dimensional (3D) hyperhoneycomb phase is still rare, despite its appeal as a battery cathode and as a Kitaev spin-liquid candidate. Here, we report pressure-induced phase transitions of Li2SnO3, from the ambient-pressure honeycomb phase to a hyperhoneycomb phase at 3 GPa, and subsequently to a Li2PbO3-type phase at 8 GPa. By integrating analyses of octahedral connectivity and Madelung energy, together with machine-learning-assisted molecular dynamics simulations, we established the thermodynamic landscape governing these transitions. Specifically, the hyperhoneycomb structure becomes competitive with the honeycomb structure under pressure and is stabilized by elevated temperatures, whereas the Li2PbO3-type structure stabilizes only at high pressures. This framework rationalizes the entire sequence of observed pressure-induced phase transitions. Furthermore, the hyperhoneycomb phase is accessible across the entire solid solution of Li2(Sn1–xRux)O3, although Ru-rich compositions require higher pressure. Remarkably, the phase-pure hyperhoneycomb x = 0.75 exhibits complete electrochemical lithium deintercalation. Given the prevalence of 2D oxides under ambient conditions, designing hyperhoneycomb phases via pressure highlights a hidden yet attractive chemical space of 3D polymorphs, offering new chemical landscapes and exotic functionalities.</p
Experimental study of biocompatible polycaprolactone composite membranes blended with short oligomers of biosourced triarylmethane-based polyaryletherketone
No full textInternational audienceOur first original goal was to synthesize new poly(aryl ether ketone)s by using successively one of three different triarylmethane monomers. These monomers were respectively produced from benzaldehyde, vanillin, and veratraldehyde by reaction with two molecules of phenol in excess of sulfuric acid. Thus, each monomer was allowed to react with one equivalent of 4,4′-difluorobenzophenone through a typical SNAR polycondensation in dimethylformamide without the help of toluene to afford only short oligomers of each desired poly(aryl ether ketone). After realizing their physico-chemical characterizations, the oligomers were employed as fillers added at 25 wt% to produce original polycaprolactone composite membranes via a classic solvent casting technique using chloroform, followed by the regeneration of used membranes in 2-methylfuran at room temperature. These impermeable membranes were tested for their resistances and exhibited Young's modulus values varying from 80 to 180 mPa. According to the surface wetting characterization, the surfaces of these membranes were clearly hydrophilic proven by values evolving between 63 and 76°. Less hydrophobic than pristine PCL and impermeable to water solution, the properties of our PCL composite membranes convince us to perform biocompatibility tests with cell viability found in a range of value between 71 and 87 % and a cell adhesion control dependent on the type of oligomer filler
Ni-exsolved catalysts from hard templated mesoporous LaNiO3 perovskite for highly efficient NH3 decomposition
No full textInternational audienceLaNiO3 perovskites have been recently studied for H2 production from NH3 decomposition / cracking. So far, this material has had its catalytic performance boosted along the addition of basic doping agents. Nevertheless, little attention has been paid to the potential benefit to gain from its textural properties. In this work, high specific surface area LaNiO3 were prepared through the yet never explored combination of citric acid as complexing agent, SBA-15 as sacrificial hard template (to create mesopores), and exsolution (to expose and activate Ni). After removal of the template, the resulting mesoporous LaNiO3 reached a specific surface area as high as 200 m2/g. In a second step, Ni nanoparticles were exsolved to reach the final catalyst, yielding 89 % NH3 conversion at 550 °C and a GHSV of 30 000 mL/gcata.h, with a stability of at least 72 h. Due to the extended specific surface area of LaNiO3, exsolved Ni nanoparticles were highly dispersed which greatly enhanced the catalytic performance. This catalyst achieved a H2 formation rate of 29 mmol/gcata.min which is higher than any previously reported doped LaNiO3. This work demonstrates the feasibility to produce both noble metal and promoter-free LaNiO3 being particularly active and stable in efficient H2 production from NH3 decomposition
A Remarkable Catalyst-Free Photochemical Alkene Hydrophosphination with Bis(trimethylsilyl)phosphonite
No full textInternational audienc
Highly efficient Hydrogenative depolymerisation of Polycaprolactone to 1,6-hexanediol
No full textInternational audienceWe report here our study on the development of an efficient process to make 1,6-hexanediol from the hydrogenation of polycaprolactone assisted by ethanolysis. Using a ruthenium SNS pincer catalyst, a record high turnover number of 19,600 with 98% yield of 1,6-hexanediol is obtained at 80 o C and 60 bar H2 pressure. The reported method has environmental advantages over the conventional process for the production of 1,6-hexanediol, which emits a significant amount of nitrous oxide greenhouse gas