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International audience; This work focuses on the impact of sulfonated Poly(Ether Ether Ketone) (sPEEK) membrane pretreatments on fuel cell performance, starting from two different batches of Fumapem E730 from Fumatech, acquired in 2019 and in 2020. sPEEK membranes are possible lower cost alternatives to PerFluoroSulfonic Acid (PFSA) membranes for Proton Exchange Membrane Fuel Cells (PEMFC) applications. Before use, they must be pretreated to ensure a complete protonic substitution and removal of residual reagents/solvent: the simplest protocol consists in soaking the membrane in an acid solution followed by a rinsing step in water. In addition to this acidification step, hydrothermal (HT) treatments in water at high temperature for a few hours to a few days were also considered herein, as well as a hydro-alcoholic (HA) step, because of their expected effects on membrane nanostructure. Overall, four different protocols were used. The membrane water uptake, water self-diffusion, proton conductivity, and fuel cell performance-under H2/O2-were measured. It was found that in the best case-membranes from the 2020 batch subjected to HA followed by 72 hours HT pretreatments-the fuel cell performances exceeded those obtained with a PFSA membrane (Nafion XL). This is explained by a higher protonic conductivity, probably resulting from a better sPEEK nano-structuration.

We recently presented the elaboration and functional properties of a new generation of hybrid membranes for PEMFC applications showing promising performances and durability. The strategy was to form, inside a commercial sPEEK membrane, via in situ sol–gel (SG) synthesis, a reactive SG phase able to reduce oxidative species generated during FC operation. In order to understand structure-properties interplay, we use a combination of direct space (AFM/3D FIB-SEM) and reciprocal space (SANS/WAXS) techniques to cover dimensional scales ranging from a hundred to few nanometers. AFM modulus images showed the SG phase distributed into spherical domains whose size increases with the SG uptake (ca. 100–200 nm range). Using contrast variation SANS, we observed that the sPEEK nanostructure is mostly unaffected by the insertion of the SG phase which presents a fractal-like multiscale structure. Additionally, the size of both the particles (aggregates/primary) is much too large to be sequestered in the ionic pathways of sPEEK. These findings indicate that the SG-NPs mainly grow within the amorphous interbundle domains. Noticeable rightward shift and widening of the ionomer peak are observed with the SG content, suggesting ion channel compression and greater heterogeneity of the ionic domain size. The SG phase develops in the interbundle regions with a limited impact on the water uptake but leading to a discontinuity of ionic conductivity. This Fourier and real spaces study clarifies the structure of the hybrid membranes and brings into the question the ideal distribution/localization of the SG phase to optimize the membrane's stabilization.

International audience; We describe a process for transferring a 200 nm thick, 200 mm wide monocrystalline silicon (mono c-Si) thin film from a silicon-on-insulator onto a flexible polymer substrate. The result is a stretchable and flexible ultra-thin semiconductor film that can be subjected to tensile stress experiments. The process uses off-the-shelf 200 mm wafers and standard polymer temporary bonding techniques. The backside substrate and buried oxide are removed using grinding and wet etching processes. No cracks or wrinkles are observed on the film prior to the tensile stress experiments. The stretching of the flexible structure results in up to 1.5% uniaxial tensile elastic strain on the thin mono c-Si film.

Polyamides belong to the major class of engineering polymers with very attractive properties but fail in a brittle manner under stress concentrators. PA6/ABS blends are well-established commercial materials due to their stiffness/toughness balance even when stress concentrators are present. The pair PA6/ABS is immiscible and exhibits poor mechanical properties due to unfavorable interactions, thus, an efficient compatibilization is mandatory for practical applications. Deep understanding of the processing-structure-properties interplays requires multiple characterization techniques to provide insights on the impact of the processing/compatibilization on morphology and phases' distribution. In this work an advanced co-localized AFM-Raman strategy was used to study the compatibilization of PA6/ABS blends with SAN-g-Maleic Anhydride. AFM and TEM allowed nanomechanical analysis and characterization of the blends' morphologies. Co-localized AFM-Raman provided new fundamental insights on the compatibilizer's effect on the PA6's γ polymorphic crystallization. The amount and distribution of this γ phase were found to depend on the blending protocol.

Proton-Exchange Membrane Fuel Cells is a promising emission free energy technology. New generation of hybrid membrane for hydrogen fuel cells were produced from commercial sPEEK membranes, chemically and mechanically stabilized with a Sol-Gel (SG) phase. To study the process-structure-properties relationship of our alternative membranes we coupled Atomic Force Microscopy and Raman microspectroscopy on membranes prepared by cryo-ultramicrotomy without epoxy embedding. This paper demonstrates the powerfulness of co-localized AFM-Raman analysis, revealing the inner structure of hybrid membranes. We obtained quantitative data on the diffusion/condensation of SG precursors inside the sPEEK membrane. Co-localized analyses revealed the formation of skin layers with lower SG concentration on both sides of the membrane. The diffusion of species from the SG phase at the cross-section surface was observed at the first step of fabrication (insufficient SG condensation) and disappeared after hydrothermal treatments (improved SG condensation). The nano-mechanical data revealed a densification of the SG phase through the fabrication process.

The optimization of manufacturing processes and the investigation of polymer materials during their life cycle imply an extended knowledge of the physical and chemical properties of the material. T...

Operando Raman spectroscopy and synchrotron X-ray diffraction were combined to probe the evolution of strain in Li-ion battery anodes made of crystalline silicon nanoparticles. The internal structure of the nanoparticles during two discharge/charge cycles was evaluated by analyzing the intensity and position of Si diffraction peaks and Raman TO-LO phonons. Lithiation/delithiation of the silicon under limited capacity conditions triggers the formation of "crystalline core-amorphous shell" particles, which we evidenced as a stepwise decrease in core size, as well as sequences of compressive/tensile strain due to the stress applied by the shell. In particular, we showed that different sequences occur in the first and the second cycle, due to different lithiation processes. We further evidenced critical experimental conditions for accurate operando Raman spectroscopy measurements due to the different heat conductivity of lithiated and delithiated Si. Values of the stress extracted from both operando XRD and Raman are in excellent agreement. Long-term ex situ measurements confirmed the continuous increase of the internal compressive strain, unfavorable to the Si lithiation and contributing to the capacity fading. Finally, a simple mechanical model was used to estimate the sub-nanometer thickness of the interfacial shell applying the stress on the crystalline core. Our complete operando diagnosis of the strain and stress in SiNPs provides both a detailed scenario of the mechanical consequences of lithiation/delithiation in SiNP and also experimental values that are much needed for the benchmarking of theoretical models and for the further rational design of SiNP-based electrodes.

Via SAXS, herein, we studied how a sPEEK microstructure evolves when it is immersed in water at a wide range of temperatures (20-100 °C) and time scales (from a few hours to dozens of days). In particular, we scrutinized the behavior of sPEEK at the temperature and time associated with the appearance of a well-defined nanosegregated morphology. At 80 °C, we observed nanoscale swelling along with smoothing of the water/polymer interface over a long period of time (several days). Herein, two of the main membrane properties, i.e., water uptake and proton conductivity, were studied for different immersion times and temperatures. It was found that the abovementioned properties were remarkably correlated with the evolution of the membrane microstructure, which was partly conserved after drying. The present findings helped us to understand that the thermally activated evolutions observed at both the nanoscale and macroscale were associated with the sPEEK β-relaxation crossover. Therefore, the very different swelling behaviors of sPEEK and Nafion are correlated to the much higher β-relaxation of sPEEK vs. Nafion (75 °C vs. -20 °C - dry state). From a practical viewpoint, this study emphasizes, for membranes alternative to Nafion, the importance and impact of the membrane pretreatment on their functional properties.

New proton-conducting co-networks were synthesized, characterized and tested as Polymer Exchange Membranes for Fuel Cells application. The membranes were obtained from 2-acrylamido-2-methylpropane sulfonic acid (AMPS) copolymerized with a perfluoropolyether oligomer used as crosslinker (Fluorolink ® FMD700). The structure, the thermo-mechanical behavior, the transport properties and the stability were examined in function of the co-network composition, e.g. increasing amount of conductive AMPS. High proton conductivity (1.10 –3 –5.10 −3 S cm −1 ) was reached at a threshold composition of 10 wt% AMPS, which also corresponds to a significant increase in water sorption. The efficiency of proton transfer was shown to directly correlate to the phase-separated nanostructures. On increasing the AMPS content, hydrophilic clusters embedded in the mechanically-robust FMD700 percolate and a co-continuous 3D morphology is formed. Fuel cells tests performed using the high-AMPS content crosslinked membranes showed behaviors comparable to benchmark Nafion ® under similar conditions, with performances significantly improved when the temperature is increased.

Gold nanoparticles, capped by 3-mercapto propane sulfonate (Au-3MPS), were synthesized inside a swollen sulfonated poly(ether ether ketone) membrane (SPEEK). The formation of the Au-3MPS nanoparticles in the swollen sPEEK membrane was observed by spectroscopic and microscopic techniques. The nanocomposite containing the gold nanoparticles grown in the sPEEK membrane, showed the plasmon resonance λmax at about 520 nm, which remained stable over a testing period of three months. The size distribution of the nanoparticles was assessed, and the sPEEK membrane roughness, both before and after the synthesis of nanoparticles, was studied by AFM. The XPS measurements confirm Au-3MPS formation in the sPEEK membrane. Moreover, AFM experiments recorded in fluid allowed the production of images of the Au-3MPSatsPEEK composite in water at different pH levels, achieving a better understanding of the membrane behavior in a water environment; the dynamic hydration process of the Au-3MPSatsPEEK membrane was investigated. These preliminary results suggest that the newly developed nanocomposite membranes could be promising materials for fuel cell applications.

Fuel cell tests have been performed on sulfonated Poly(Ether Ether Ketone) (sPEEK) membranes using dry gases. Impact of gas stoichiometry on performance evolution and membrane–electrodes assembly's water distribution optimization (water management) was studied. During the tests, output voltage evolution was recorded as well as impedance spectra, polarization curves and water amount collected at both sides. Fuel cell performances were observed to be influenced by water management which depends on both operating conditions and membrane intrinsic properties. Increasing either hydrogen or oxygen stoichiometry leads to a decrease of performance. This effect was more pronounced for hydrogen increase (anode). This has been ascribed to a global drying of the membrane along with the appearance of a heterogeneous hydration both through the MEA and along the gas channels. Cell performance characterization during the membrane lifespan was mainly based on Electrochemical Impedance Spectroscopy measurements and showed that water distribution heterogeneity increased with operating time for sPEEK membrane, leading to a drop of performance. This was mainly ascribed to the drying of the gas inlet and the increased hydration at the gas outlet. These behaviours were not observed for the better performing Nafion, which underlines the impact of membrane water transport properties on fuel cell performance.

By copolymerization of the disodium-2,2′-disulfonate-4,4′-oxydibenzoic acid (SODBA), the 4,4′-oxybis(benzoic acid) (OBBA) with the bis 3,4-(diaminophenyl)sulfone (BDAPS), a series of high molecular weight sulfonated polybenzimidazoles (sPBI) were prepared by varying the ratio of monomers SODBA/OBBA. Polymers with ion exchange capacity (IEC) ranging from 0 to 3.2 meqH+/g were obtained. The chemical structure of the sPBI was confirmed by NMR, Fourier-transform infra-red (FTIR). Although the sPBI display a very poor solubility in organic solvents, they are, in the ammonium salt form, soluble in polar aprotic solvents such as DMF, NMP, or DMSO. Tough and ductile membranes from solution casting method were prepared. The water uptake and the ionic conductivity were determined at 30 and 90 °C. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1732–1742, 2010

In the present work, a new sulfonated tetraamine and the corresponding sulfonated polybenzimidazoles (sPBI) were synthesized. For the sake of determining the best polymerization conditions, a study involving model compounds was first performed. A strong acid medium was used as polymerization solvent, which allowed to obtain high molecular weight sPBI. A series of polymers with ion exchange capacity (IEC) ranging from 0 to 2.6 mequiv/g were synthesized using a non-sulfonated tetraamine as a comonomer. The chemical structure of those polymers was confirmed by nuclear magnetic resonance (NMR) and Fourier transform infrared (FTIR) as well as by titration. Thermogravimetric analysis (TGA) and viscosity measurement were performed as well. On the other hand, different architectures of the copolymers were prepared, i.e., random, sequenced copolymers, and blends of the homopolymers. The membranes prepared from the sPBI display low water uptake. The ionic conductivities measured in the hydrated state at room temper...

International audience; The design of interpenetrated networks (IPN) membranes for fuel cell applications requires both an electrolyte and a neutral network. The composition and architecture of the latter are of major importance for the final IPN membrane properties. In this work, networks based on a fluorinated diepoxy oligomer (DFODDE) and a non-fluorinated triepoxy monomer (TMPTGE) were synthesized. The network composition was varied from 100% DFODDE to 100% TMPTGE, resulting in an increase of the crosslinking density and concomitantly a decrease of the fluorine content. The curing process was optimized to achieve a total epoxy conversion and the chemical structure of the networks was characterized by Raman and Infrared spectroscopies. The physical, thermal and chemical membrane properties were studied and discussed as a function of the crosslinking density and of the fluorine content. Increasing the crosslinking density led to a decrease of the membrane permeability to oxygen. Water sorption properties depended on both parameters, with a prevailing role of the fluorine content on the water uptake and a major influence of the crosslinking density on the diffusion parameter. The thermal stability increased also with the fluorine content. All materials exhibited a good stability in water at 80 degrees C but a significant weight loss after immersion in a concentrated H2O2 solution. Altogether, these results indicate that networks containing 20% of TMPTGE exhibit an interesting set of properties (low oxygen permeability, high T-g, good chemical and thermal stability) to behave as a neutral partner in an IPN membrane. Moreover, the low water uptake and diffusion rate measured in these networks make them attractive for water barrier membranes.

International audience; Silica (SiO$_2$) nanoparticles (NPs) were func-tionalized by silanization to produce a surface covered with organosiloxanes. Information about the surface coverage and the nature, if any, of organosiloxane polymerization, whether parallel or perpendicular to the surface, is highly desired. To this extent, two-dimensional homonuclear $^{29}$Si solid-state NMR could be employed. However, owing to the sensitivity limitations associated with the low natural abundance (4.7%) of $^{29}$Si and the difficulty and expense of isotopic labeling here, this technique would usually be deemed impracticable. Nevertheless, we show that recent developments in the field of dynamic nuclear polarization under magic angle spinning (MAS-DNP) could be used to dramatically increase the sensitivity of the NMR experiments, resulting in a timesaving factor of ∼625 compared to conventional solid-state NMR. This allowed the acquisition of previously infeasible data. Using both through-space and through-bond 2D $^{29}$Si− $^{29}$Si correlation experiments, it is shown that the required reaction conditions favor lateral polymerization and domain growth. Moreover, the natural abundance correlation experiments permitted the estimation of $^2J^{Si−O−Si}$-couplings (13.8 ± 1.4 Hz for surface silica) and interatomic distances (3.04 ± 0.08 Å for surface silica) since complications associated with many-spin systems and also sensitivity were avoided. The work detailed herein not only demonstrates the possibility of using MAS-DNP to greatly facilitate the acquisition of 2D $^{29}$Si− $^{29}$Si correlation spectra but also shows that this technique can be used in a routine fashion to characterize surface grafting networks and gain structural constraints, which can be related to a system's chemical and physical properties.

Silicon is being considered as one of the most promising anode materials for next generation lithium-ion batteries due to its high theoretical capacity (3580 mA h g-1 at room temperature) (1). Upon charging, Si and Li react via an alloying process with a sharp interphase separating the growing LixSi amorphous phase from the pristine crystalline Si. In case of spherical particles this leads to a core-shell structure captured in Figure1a. The alloying process leads to an enormous volume expansion of Si resulting in cracking of the electrode material and rapid fading of its performance that impedes the commercialization of Si-based anodes. Nevertheless below a critical particle diameter of 150nm volume expansion does not lead to cracking (2). In order to profit from silicon unique properties, the structural evolution along charging/discharging must be understood. Using ex situ Raman spectroscopy we observed the gradual transformation of initially crystalline silicon into amorphous one upon cycling. The resulting stresses generated in the crystalline cores of the core-shell structures were probed as well as their evolution along lithiation/delithiation. The changes of the crystalline lattice during the initial cycles were also monitored using operando synchrotron X-ray diffraction (XRD). In addition we were able to further quantify the constrained/unconstrained state of the silicon core. We show that combined ex situ Raman spectroscopy and in situ XRD provide in-depth understanding of the nanoparticles evolution. Figure 1 . Schematic representation of silicon electrodes: a) Formation of a core-shell structure upon cycling, b) Influence of the laser power on the Raman signal and c) Gradual amorphization of the electrode along cycling (All spectra were normalized to the maximum of the c-Si peak) 1. Obrovac, M. N., and Leif Christensen. "Structural changes in silicon anodes during lithium insertion/extraction." Electrochemical and Solid-State Letters 7.5 (2004): A93-A96. 2. Liu, Xiao Hua, et al. "Size-dependent fracture of silicon nanoparticles during lithiation." Acs Nano 6.2 (2012): 1522-1531. Figure 1

Core-shell structural evolution of crystalline silicon nanoparticles upon lithiation/delithiation by ex situ Raman spectroscopy and operando synchrotron X-ray diffraction Silicon has attracted substantial attention as an alternative anode material for next-generation Li-ion batteries (LiBs) as it has a high theoretical capacity of 3580 mA h g-1 that is about ten times that of the commonly used graphite. (1) Upon charging, Si and Li react via an alloying process with a sharp interphase separating the growing LixSi amorphous phase from the pristine crystalline Si. In case of spherical particles this leads to a core-shell structure captured in Figure1b and c. An enormous volume expansion of Si associated with alloying leads to cracking of the electrode material and rapid fading of its performance. This hinders Si from being widely used in LiBs. It has been reported that for Si nano-particles (diameter In the present work we were able to evidence the gradual amorphisation of crystalline Si nanoparticles upon cycling using ex situ Raman spectroscopy. Furthermore we probed the resulting stresses found in cores of the core-shell structures of Si nanoparticles and their evolution along lithiation/delithiation. Operando synchrotron X-ray diffraction (XRD) has also been performed to monitor the changes of the crystalline lattice during the initial cycles and to further quantify the constrained/unconstrained state of the silicon core. By means of combined ex situ Raman spectroscopy and in situ XRD we were able to provide in-depth understanding of the nanoparticles evolution. Figure 1 . Schematic representation of silicon electrodes: a) pristine b) after 1 cycle lithiation c) after 100 cycles lithiation d) corresponding Raman spectra. Black, blue and green, respectively. (All spectra were normalized to the maximum of the c-Si peak) 1. Obrovac, M. N., and Leif Christensen. "Structural changes in silicon anodes during lithium insertion/extraction." Electrochemical and Solid-State Letters 7.5 (2004): A93-A96. 2. Liu, Xiao Hua, et al. "Size-dependent fracture of silicon nanoparticles during lithiation." Acs Nano 6.2 (2012): 1522-1531. Figure 1

The hydrolytic degradation mechanism of sulfonated polyimide (sPI) membranes was determined through the study of model compounds and validated with a fully sulfonated polymer. Two model compounds characteristic of the ionic sequence and of the junction between ionic and neutral sequences in block copolymers were synthesized and aged in water at different temperatures. Liquid chromatography was used to separate and identify the degradation products by means of various spectroscopies (IR, UV, NMR). It is shown that the hydrolysis of the naphthalenic imide rings is an equilibrated reaction and that the imide rings are more stable when located between ionic substituted monomer than in the hydrophilic–hydrophobic junctions. It is concluded that block copolymers with long ionic sequences or blends of sulfonated and non sulfonated homopolymers should be more stable than random copolymers. This conclusion is confirmed by the study of the hydrolytic degradation of fully sulfonated polyimide.

Poor durability of polymer electrolyte membranes is one of the most limiting factors of proton exchange membrane fuel cell (PEMFC). Hydrogen peroxide which is formed electrochemically or chemically during operation is one of the potential deteriorating factors, particularly for polyaromatic membranes. To be able to increase membrane durability, the aging path involved must be elucidated. To give an insight into the degradation mechanism of sulfonated polyaryl ether ketones (sPAEK) a study on model compound has been performed. Each species produced has been collected by liquid chromatography and identified by NMR, IR and mass spectroscopies. We have demonstrated that degradation proceeds through the addition of a hydroxyl radical on the aromatic ring. Then, the oxidation of these phenolic groups leads to several chain scissions. On the basis of these experiments, a strategy can be drawn to improve the membrane durability.

Ex situ hydrolytic stability of sulfonated polyimide (s-PI) membranes for fuel cells was studied depending on structural and external parameters including the ion exchange capacity, the block character, the temperature and the hydrogen peroxide concentration. Infrared spectroscopy was used to identify and quantify the chemical modifications such as the loss of imide functions and of ionic monomers. The decrease in ion exchange capacity due to the elution of sulfonated oligomers was confirmed by sulfur content analysis. A complete hydrolysis of some of the imide functions is observed leading to polymer chain scissions and to the loss of the mechanical properties. It is shown to be a thermo activated process and the activation energy (60 kJ/mol) is found in good agreement with the value determined from fuel cell lifetimes. The degradation in fuel cell conditions is similar but faster than in pure water. The same kinetic can be reproduced ex situ by addition 0.05% of hydrogen peroxide.

The stability of sulfonated polyimide (sPI) membranes in fuel cell conditions was studied under stationary and cycling electric loading conditions. The lifetime in operating conditions was shown to vary from few tens to several hundreds of hours depending on both the membrane ion content and the fuel cell temperature. The membrane degradation is shown to be a thermoactivated process and activation energies have been extracted (70–110 kJ). The membrane post-mortem analysis by infrared revealed a significant chemical degradation which was identified as the imide function hydrolysis inducing polymer chain scissions and consequently the loss of the mechanical properties. In addition to this main degradation process, the infrared analysis of the membrane surface exposed to the anodic compartment suggests the occurrence an additional oxidative process. sPI membranes exhibit a lower sensitivity to operation under electric loading cycling compared to Nafion.

Proton-Exchange Membrane Fuel Cells (PEMFC) have emerged as promising emissionfree energy conversion devices. However, the ionomer membrane at the heart of the device fails to continually perform over the desired time (8000 h for transportation and 50000 h for stationary) with a high temperature (100–150 °C vs 80 °C for std Nafion) and at low humidity (30 %RH) ranges. The aim of this work is to improve existing membranes by introducing stabilizing additives by Sol-Gel (SG) chemistry. SG precursors are selected to diffuse and selfcondense inside commercial membranes allowing for the introduction and immobilization of the stabilizing groups without influencing the proton conductivity, mechanical properties and permeability of the membranes. The SG phase is designed to protect against oxidation and limits dimensional changes that lead to ageing of the membrane during in-cell operation. An extensive list of antioxidant functions exists, and it was decided to use the functions thiourea, thiol, phenol hindered as sacrificial stabilizing functions for their high reactivity in the presence of hydrogen peroxide already presented in the literature. Stabilization by inserting a regenerable radical inhibitor, such as cerium ions, is also envisaged. The morphology (size, interaction/dispersion, connectivity) and localization (polar/apolar regions) of the SG phase will depend on the chemical affinity and are parameters expected to be crucial for properties (H+ conductivity, water uptake), durability (H2O2-accelerated aging tests to assess the effectiveness of the reactive SG phase) and performances (FC operation) of the hybrid membranes. Consequently, this study explores the morphology obtained (mass fractal structure vs. dispersed spherical aggregates vs. interconnected ones) at all relevant length scales using a combination of direct space (AFM/SEM/TEM) and reciprocal space (contrast variation SANS/SAXS) techniques (dimensional scale covered : from a hundred to a few nanometers). H2O2-accelerated ex situ aging tests and fuel cell tests show promising operability of the hybrid membranes and the potential of the SG phase to inhibit the chemical ageing of sPEEK.; Les piles à combustible à membrane échangeuse de protons (PEMFC) sont des dispositifs prometteurs de conversion d’énergie sans émission. Cependant, la membrane ionomère au cœur de l’appareil ne parvient pas à délivrer des performances durables (à atteindre : 8000 h pour le transport, 50000 h pour le stationnaire) à haute température (100–150 °C contre 80 °C pour le Nafion) et à faible humidité relative (30 %HR). L’objectif de ces travaux est d’améliorer des membranes commercialisées en introduisant des additifs stabilisants par chimie SolGel (SG). Les précurseurs de SG sont sélectionnés pour diffuser et autocondenser à l’intérieur des membranes permettant ainsi l’introduction et l’immobilisation de groupements stabilisants sans influencer la conductivité protonique, les propriétés mécaniques et la perméabilité des membranes. La phase SG est conçue pour limiter le vieillissement chimique (protection contre l’oxydation) et physique (limitation des variations dimensionnelles) de la membrane lors du fonctionnement en pile. Une large liste de fonctions antioxydantes existe et nous avons décidé d’étudier les fonctions thiourée, thiol, phénol encombré comme fonctions stabilisatrices sacrificielles pour leur grande réactivité déjà connue de la littérature en présence de peroxyde d’hydrogène. Une stabilisation par l’insertion d’inhibiteur radicalaire, comme les ions cérium, est également envisagée. La morphologie (taille, interaction/dispersion, connectivité) et la localisation (régions polaires/apolaires) de la phase SG dépendront de l’affinité. Ces paramètres sont cruciaux pour les propriétés (conductivité H+, absorption d’eau), la durabilité (vieillissement accéléré par H2O2 pour évaluer l’efficacité de la phase réactive SG) et les performances (fonctionnement FC) des membranes hybrides. En conséquence, cette étude propose une exploration de la morphologie obtenue (structure fractale vs agrégats sphériques dispersés vs agrégats interconnectés) à toutes les échelles de longueur pertinentes (de la centaine à quelques nanomètres) en utilisant une combinaison de techniques d’espace direct (AFM/SEM/TEM) et d’espace réciproque (variation de contraste SANS/SAXS). Les tests de vieillissement accéléré ex situ par H2O2 et les tests en pile à combustible montrent une opérabilité prometteuse des membranes hybrides et le potentiel de la phase SG à inhiber le vieillissement chimique du sPEEK.

The comprehension of the intrinsic characteristics and interactions found in complex polymeric systems is important and challenging for the development of new engineering solutions. In order to elucidate the process-structure-properties interplays, the co-localization of different information becomes essential, to obtain reliable answers. The characterization of both the surface and the bulk of materials is also of prime importance, especially for thin polymeric materials (, L’étude avancée de systèmes polymères complexes (mélanges compatibilisés, nanocomposites, copolymères à bloc, etc) est cruciale pour le développement de nouvelles solutions d'ingénierie. Afin d'élucider les relations mise en œuvre-structure-propriétés de ces systèmes, la co-localisation d’informations chimique, physique et morphologique devient essentielle pour obtenir des réponses fiables. La caractérisation de la surface et de l’intérieur des matériaux est également d'une importance primordiale, en particulier pour les matériaux polymères minces (

Fuel cell is a promising solution for clean production of hydrogen based energy. However to achieve a large-scale deployment of this technology, issues remain to be addressed. One of the remaining problems concerns the heart of the cell (polymer membrane sandwiched between two electrodes). We can stress the fact that it is impossible to improve the catalyst efficiency and the cell performance by a simple increase of the operating temperature (100-120 °C). Indeed the reference membrane (Nafion) exhibit a step decrease of its thermomechanical properties beyond 80 °C, whereas alternative membranes (with a better thermomechanical stability) are victims of a much faster chemical aging resulting into unexpected failure of the device.Our main objective is to develop novel hybrid membranes consisting of a commercial ionomer matrix in which we will introduce precursors capable to form a sol-gel phase. It will result on membrane composed of two interpenetrating phases, an ion conductive non-crosslinked polymer phase and a crosslinked inorganic phase providing chemical and thermomechanical stabilization. The control of the chemistry of this sol-gel phase, its morphology and its location in the membrane, which will improve the membrane properties, are essential to consider the development of these membranes for fuel cells.A careful analysis of the hydrothermal treatment effect on the microstructure of sPEEK membranes has been performed. Thanks to this analyse we can relate the microstructure with the functional properties of the polymer. The sol-gel process enables the growth of the sol-gel phase without disturbance of the initial nanostructured membrane. This strategy makes possible to control the distribution and morphology of the inorganic phase.The elaboration process of hybrid membrane has been studied. We presented the influence of elaboration parameters regarding the best conditions to prepare an optimized hybrid membrane. The physical and chemical properties of the inorganic phase were evaluated by many techniques (SANS, IR, DMA, etc.). The influence of the chemical structure (cross-linking degree) of the sol-gel network andthe impact of the sol-gel content and its distribution (morphology) into the host membrane on their functional properties is presented. We observed the great influence of cross-linking degree and of the amount of sol-gel present in the membrane which determines the functional properties of the membrane., La pile à combustible est une solution d'avenir pour produire de l'électricité propre. Cependant des problèmes technologiques limitent pour le moment un déploiement à grande échelle. C’est au cœur de pile et plus particulièrement de la membrane conductrice ionique séparant l’anode et la cathode, que certaines difficultés se posent. Nous pouvons ainsi citer l’impossibilité d’améliorer l’efficacité du catalyseur et le rendement du dispositif en augmentant simplement la température de fonctionnement (100 - 120°C). En effet, la membrane de référence (Nafion) perd ses propriétés thermomécaniques au-delà de 80°C, alors que les membranes alternatives (offrant une meilleure stabilité thermomécanique) sont victimes d’un vieillissement chimique trop rapide qui induit un arrêt inopiné du dispositif. Pour lever ce verrou technologique, nous proposons une nouvelle stratégie qui repose sur le développement de membranes nano-composites constituées d'une matrice ionomère commerciale (non réticulée) dans laquelle nous introduirons des précurseurs aptes à former une phase sol-gel offrant une stabilisation chimique et thermomécanique (réticulée). C'est le contrôle de la chimie de ce réseau, de sa morphologie et de sa localisation dans la membrane hôte qui permettra l'amélioration des propriétés de la membrane hybride ainsi obtenue.Nous avons réalisé une analyse minutieuse de l'effet d’un traitement hydrothermique sur la microstructure des membranes sPEEK. Grâce à cette analyse nous pouvons relier la microstructure avec les propriétés fonctionnelles de l’ionomère pour obtenir des membranes sPEEK mieux nanostructurées et donc plus performantes. Le procédé sol-gel permet la croissance de la phase sol-gel sans perturbation de la nanostructuration initiale de l'ionomère. Cette stratégie permet donc de contrôler la distribution et la morphologie de la phase inorganique.Le processus d'élaboration des membranes hybrides a été étudié. Nous avons étudié l'influence des paramètres de fabrication sur les propriétés des membranes hybrides, et ainsi pu produire des membranes hybrides optimisées. Les propriétés physiques et chimiques de ces membranes ont été évaluées par de nombreuses techniques (SANS, IR, DMA, etc.). L'influence de la structure chimique (degré de réticulation) du réseau sol-gel des membranes hybrides et l'impact de la teneur en sol-gel et de sa distribution (morphologie) dans la membrane hôte sur les propriétés fonctionnelles sont présentés. Nous observons une grande influence du dégrée de réticulation et de la quantité de sol-gel présent dans la membrane qui conditionne les propriétés fonctionnelles de la membrane.

Fuel cells as production system of clean and sustainable energy will help to protect our ecosystem by providing an alternative to fossil fuels before their total exhaustion. However, lower costs and a greater durability are needed for these systems and more particularly the center of the cell, naming the membrane-electrodes assembly (MEA). This study was performed on a sulfonated poly-aromatic membrane: sulfonated polyetheretherketone, or sPEEK. This alternative membrane, which possesses only poor chemical stability, offers a much better thermomechanical behavior than Nafion®, the reference membrane. Aim of this study was first to understand the impact of operating conditions on fuel cell performance, for a sPEEK membrane, in order to improve performance, but also to better understand the impact of the membrane chemical aging onto its physicochemical properties and the resulting fuel cell performance. First the behavior of sPEEK in fuel cell for different operating conditions showed that water transport in the MEA is critical for fuel cell performance. Indeed a very high heterogeneity of operation due to slow water transport in the sPEEK membrane was observed, resulting in a major drop of fuel cell performance compared with what observed using Nafion®. As in situ diagnosis of membrane degradation is difficult and the system particularly complex, it was then decided to study "ex situ" the chemical aging of the membrane (laboratory conditions). Aged membranes under the action of H2O2 (oxidative responsible for the in situ chemical aging of the membranes) were characterized and finally tested in fuel cell. It appears that the chemical aging results in chains scissions, which induce an increase of the membrane swelling. For too much aging, these chains scissions result in the membrane loss of mechanical strength, incompatible with their use in fuel cell. However, for controlled aging (very low degradation), the induced chemical changes allow better swelling of the membrane resulting in an increase of the conductivity and better water transport in the MEA, making it possible to reach, with sPEEK, as good performance as with the use of Nafion®.; La pile à combustible comme moyen de production d'énergie propre et durable participera à la protection de l'écosystème en permettant à la filière hydrogène d'offrir une alternative aux énergies fossiles avant leur total épuisement. Cependant une baisse des coûts et une plus grande durabilité sont indispensables pour ces systèmes et notamment le cœur de pile, constitué d'un assemblage membrane-électrodes (AME). Cette étude a été menée sur une membrane alternative poly-aromatique sulfonée : le PolyEtherEtherCétone sulfoné, ou sPEEK. Cette membrane, qui n'offre qu'une stabilité chimique médiocre, a l'avantage d'offrir une bien meilleure tenue thermomécanique que la membrane de référence Nafion®. Le but de cette étude fut donc d'évaluer l'influence des conditions de fonctionnement sur les performances de la pile utilisant une membrane sPEEK, dans le but de les améliorer, mais aussi de mieux comprendre l'impact du vieillissement chimique de cette membrane sur ses propriétés physicochimiques et sur ses performances en pile. Ce travail fut réalisé en deux temps. Tout d'abord l'étude du comportement de la membrane sPEEK en pile pour différentes conditions d'utilisation a montré que le transport de l'eau dans l'AME est un point déterminant des performances de la pile. En effet une très forte hétérogénéité de fonctionnement imputable à la mauvaise répartition de l'eau dans la membrane sPEEK a été observé, aboutissant à des performances fortement dégradées par rapport à celles du Nafion®. Le diagnostic in situ de la dégradation de la membrane étant difficile et le système particulièrement complexe, il fut ensuite décidé d'étudier « ex situ » le vieillissement chimique de la membrane (dans des conditions de laboratoire). Les membranes vieillies sous l'action de H2O2 (oxydant responsable du vieillissement chimique des membranes en pile) ont ensuite été caractérisées et enfin testées en pile. Il apparaît que le vieillissement chimique résulte en des coupures des chaînes polymère, qui induisent une augmentation du gonflement de la membrane. Pour de forts vieillissements, ces coupures de chaînes entraînent une perte de la tenue mécanique de la membrane, incompatible avec une utilisation en pile. Cependant, pour des vieillissements contrôlés (très faible degré d'avancement), les modifications chimiques induites permettent un meilleur gonflement de la membrane qui résulte en une augmentation de sa conductivité ainsi qu'un meilleur transport de l'eau en pile, permettant d'obtenir des performances comparables à celles du Nafion®.

One of the origins of the accelerated aging of proton exchange membranes used in Fuel Cells is the oxidation induced by H2O2 formation. This work concerns the development of a new way to chemically stabilize a sPEEK membrane by the addition of stabilizing nano-fillers. Four fillers were synthesized by grafting organosulfur functions (disulfide, tetrasulfide and thiourea) onto silica nanoparticles. A specific protocol to prepare hybrid membranes led to materials with suitable mechanical properties and proton conductivity for fuel cells application. Polysulfides allow a significant decrease of the matrix degradation occurring during membrane processing and also a large increase of the proton conductivity of this matrix during ex-situ aging tests (H2O2). A membrane containing tetrasulfide nano-fillers could withstand 1200h in OCV condition at 70°C and 100%RH, without showing any sign of degradation., La dégradation accélérée des membranes conductrices protoniques en pile est en partie due à une oxydation induite par la production d'H2O2. Cette étude présente une stratégie originale de stabilisation chimique d'une matrice de sPEEK par l'inclusion de nano-charges stabilisantes. Quatre nano-charges ont été préparées par fonctionnalisation de nanoparticules de silice avec des fonctions chimiques organosoufrées (disulfure, tétrasulfure et thiourée). Un protocole spécifique de mise en forme des membranes hybrides a permis d'obtenir des composites présentant des propriétés mécaniques et une conductivité protonique compatibles avec l'application pile. Les fonctions polysulfures permettent de ralentir la dégradation de la matrice de sPEEK durant l'étape de mise en œuvre et d'augmenter sa conductivité au cours d'un vieillissement ex-situ (H2O2). En présence de fonctions tétrasulfures, la membrane sPEEK ne se dégrade pas durant un test de 1200h en OCV à 70°C et 100%HR.

Fuel cell development requires an improvement in the electrode-membrane assembly durability which depends on both the polymer used and the fuel cell operating conditions. The origin of the degradation can be either electrochemical, chemical and/or mechanical. This study deals with the understanding of alternative membranes ageing mechanisms, i.e. non fluorinated membranes, such as sPEEK and sPI. For this kind of membranes, the first process is chemical. Understanding these mechanisms is the first essential step to develop more stable structures. An original approach is developed to overcome the analytical difficulties encountered with polymers. It consists in studying the degradation mechanism on model structures. Ageings are carried out in water, with H2O2 in some cases (identified as a cause of membrane chemical ageing in the fuel cell system), and at different temperatures. The approach consists in separating the different products formed by chromatography. Then they are identified (NMR, IR, MS) and quantified. This method allows us to establish the ageing mechanism. We show that the ageing of a sPEEK structure mainly results from an attack by end chains which spreads to the whole. This mechanism is confirmed on ex-situ and in-situ aged membranes. These two kinds of ageing lead to an important decrease in polymerisation degree (determined by SEC). Formation of the same degradation products is observed. In fuel cell, a heterogeneous degradation is noticed. It takes place mainly on the cathode side.sPI are known for their high sensitivity to hydrolysis. Nevertheless, we highlight a limited degradation at 80°C due to the recombination of hydrolysed species at this temperature.; Le développement de la pile à combustible repose sur une amélioration de la durabilité des assemblages membrane-électrodes (AMEs). La durée de vie des AMEs dépend, entre autres, de la nature des matériaux utilisés ainsi que des conditions de fonctionnement de la pile. La dégradation peut être d'origine électrochimique, chimique, et/ou mécanique. Cette étude porte sur la compréhension des mécanismes mis en jeu lors du vieillissement de membranes alternatives, non fluorées, de type PEEKs et PIs, étape indispensable au développement de structures plus stables. Dans ce cas, le processus est avant tout chimique. Une démarche originale, qui consiste à étudier le mécanisme de dégradation sur des structures modèles, a été adoptée afin de contourner les difficultés analytiques propres aux polymères. Les vieillissements sont réalisés dans l'eau, éventuellement additionnée de H2O2 (identifié comme une des causes du vieillissement chimique des membranes en pile), à différentes températures. La démarche consiste à isoler par chromatographie les différents produits formés, à les identifier (RMN, IR, SM) et à les quantifier. Ceci nous a permis d'établir le mécanisme de vieillissement. Nous avons en particulier montré que le vieillissement d'une structure PEEKs résulte principalement d'une attaque par les bouts de chaîne qui se propage à l'ensemble. Ce mécanisme a été validé sur une membrane vieillie en ex-situ et testée en pile. Ces deux types de vieillissement conduisent à une diminution importante du degré de polymérisation (déterminé par CES) et à la formation des mêmes produits primaires de dégradation. En pile, une dégradation hétérogène est mise en évidence essentiellement côté cathode. Les PIs sont connus pour leur forte sensibilité à l'hydrolyse. Toutefois, nous avons pu montrer que la dégradation est relativement limitée à 80°C en raison d'une recombinaison des espèces hydrolysées.

Over the last years, many research works have been focused on new clean energy systems. Hydrogen fuel cell seems to be the most promising one. However, the large scale development of this technology is still limited by some key elements. One of them is the polymer electrolyte membrane Nafion® currently used, for which the ratio performance/cost is too low. The investigations we carried out during this PhD work are related to a new class of ionic conducting polymer, the sulfonated polybenzimidazoles (sPBI). Polybenzimidazoles (PBI) are aromatic heterocyclic polymers well-known for their excellent thermal and chemical stability. Ionic conduction properties are obtained by having strong acid groups (sulfonic acid SO3H) on the macromolecular structure. For that purpose, we first synthesized sulfonated monomers. Their polycondensation with an appropriate non-sulfonated co-monomer yields to sPBI with sufonation range from 0 to 100%. Three different sPBI structures were obtained, and verified by appropriate analytical techniques. We also showed that the protocol used for the synthesis resulted in high molecular weights polymers. We prepared ionic conducting membrane by casting sPBI solutions on glass plates. Their properties of stability, water swelling and ionic conductivity were investigated. Surprisingly, the behaviour of sPBI was quite different from the other sulfonated aromatic polymers with same amount of SO3H, their stability was much higher, but their water swelling and ionic conductivity were quite low. We attributed these differences to strong ionic interactions between the sulfonic acid groups and the basic benzimidazole groups of our polymers. However, we managed to solve this problem synthesizing very highly sulfonated PBI, obtaining membranes with a good balance between all the properties necessary.; Depuis de nombreuses années, on promet à la pile à combustible un avenir radieux. Cependant, le développement de cette technologie se heurte toujours à des verrous technologiques. Parmi ceux-ci se trouve la membrane polymère conductrice protonique Nafion®, élément central de la pile. Ainsi, nous nous sommes attachés dans ce travail à étudier des polymères alternatifs, les polybenzimidazoles sulfonés (sPBI). Si les polybenzimidazoles (PBI) sont bien connus pour leur remarquable stabilité thermique et chimique, leur utilisation en pile à combustible nécessite leur fonctionnalisation par des groupements acide sulfoniques SO3H, afin de leur conférer une bonne conduction protonique. Ainsi, la synthèse de sPBI a été réalisée par polycondensation de monomères fonctionnalisés spécialement mis au point. Nous avons ainsi pu obtenir trois séries distinctes de sPBI, présentant des Capacités d'Echange Ionique allant de 0 à 4.3 meq/g. Toutes les structures de ces polymères ont été vérifiées par différentes techniques analytiques, et il a été montré que le protocole de synthèse retenu permettait d'obtenir des masses molaires supérieures à celle reportées jusque là dans la littérature. A partir de ces polymères, des membranes ont été préparées. Leurs propriétés relatives à une utilisation en pile à combustible ont été étudiées : stabilité thermique, stabilité en milieu aqueux oxydant, gonflement à l'eau et conductivité protonique. Ces études ont mis en lumière l'existence d'interactions entre les SO3H acides et les groupements benzimidazoles basiques de ces polymères, qui influencent fortement les propriétés des ces membranes. Par rapport à d'autres polymères contenant la même quantité de SO3H, les sPBI présentent ainsi une meilleure stabilité mais des gonflements à l'eau et des conductivités plus faibles. Il a fallu atteindre des taux de sulfonation extrêmement élevés pour pouvoir s'affranchir de ce problème et obtenir des membranes ayant les qualités requises.

The durability of the bonded assemblies of the civil engineering is dealt through two complementary approaches at both the micro and the macroscales. The interfacial zone cement paste/ epoxy adhesive bond is defined by thermical micro-analysis (µTA) and electronic microscopy, that has permit to reveal the existence of an interphasis polymer and a transition zone. Further, the effect of the hygrothermical ageing is translated by the plasticization of the epoxy network in the short term and by a recovery of the reticulation process in the longer term. The mechanical resistance of the bonded assemblies is then studied by a cleavage test. Before ageing, the rupture of the bonded assemblies is generally cohesive in the cementitious support. The hygrothermical ageing causes a weakening of the interface and moves the cracking place toward the transition zone.; La durabilité des assemblages collés du génie civil est abordée à travers deux approches complémentaires aux échelles micro et macroscopiques. La zone interfaciale pâte de ciment / adhésif époxy est d'abord caractérisée par micro-analyse thermique (µTA) et microscopie électronique, ce qui a permis de révéler l'existence d'une interphase polymère (gradient de TG dans l'adhésif à proximité du substrat) et d'une zone de transition (pénétration du polymère dans le substrat). Par ailleurs, l'effet du vieillissement hygrothermique se traduit par la plastification du réseau époxy à court terme et par une reprise du processus de réticulation à plus long terme. La résistance mécanique des assemblages collés est ensuite étudiée au moyen d'un test de clivage. Avant vieillissement, la rupture des assemblages est généralement cohésive dans le support cimentaire. Le vieillissement hygrothermique engendre un affaiblissement de l'interface et déplace le lieu de fissuration vers la zone de transition