Hydrogen Resistive Sensors based on Organized Nanostructures Assembles

Les contextes mondiaux énergétiques, climatiques et économiques actuels évoluent de manières telles que le dihydrogène H2 prend une place de plus en plus importante en tant que combustible et vecteur énergétique. Le dihydrogène est un gaz incolore, inodore et non-toxique donc indécelable par les sens humains, mais il est extrêmement inflammable et explosif. De plus, H2 est caractérisé par un domaine d'explosivité très large, de 4 % à 75 % de H2 dans l'air. L'objet de ce travail de thèse a donc été de préparer des capteurs de sécurité ou de quantification originaux et ayant des performances accrues pour la détection de H2. Les capteurs préparés sont de types résistifs et les métaux sensibles utilisés sont le palladium et le platine. Afin d'améliorer les performances de détection de ces capteurs à dihydrogène, plusieurs morphologies de couches sensibles ont été conçues : des monocouches organisées à 2 dimensions de nanoparticules cœurs-coquilles Pd@Au et Pt@Au formées par la méthode de Langmuir-Blodgett ou immobilisés sur les substrats par un agent de couplage de type silane (mercaptopropyltrimethoxysilane), des dépôts physiques à 2 dimensions et des films de nanoparticules à 3 dimensions. Selon la morphologie de la couche préparée et le type de métal sensible utilisé, divers mécanismes de détection ont été mis en évidence et diverses performances de détection ont été observées (type et amplitude de réponse, gamme de détection, temps de réponse et de retour,...). Les modèles de Fuchs-Sondheimer et Mayadas-Shatzkes d'une part, et un modèle de percolation par la création de chemins de conduction d'autre part, ont permis d'expliquer les variations de résistivité électrique des couches sensibles à base respectivement de platine et de palladium lors de l'exposition à l'hydrogène.Hydrogen takes is foreseen as a generalized fuel and energy carrier. It is a colorless, odorless and non-toxic gas, and therefore it is undetectable by the human senses. Hydrogen has a severe drawback as it is an extremely flammable and explosive gas. Moreover, H2 has a wide explosive range, from 4 to 75 % H2 in air. Therefore, the aim of this PhD work was to develop safety and concentration sensors with enhanced performances. Resistive sensing layers were designed on several morphologies and sensing materials : 2D Langmuir-Blodgett organized monolayers of core-shell Pd@Au or Pt@Au nanoparticles, immobilized Pd@Au monolayer grafted through a self assembled monolayer, evaporated 2D metal films of Pt or Pd, and 3D platinum nanoparticles arrays. According to the sensing layer morphology and sensing metal, numerous sensing mechanisms and performances were demonstrated (response type and amplitude, sensing range, response and recovery times,…). Fuchs-Sondheimer and Mayadas-Shatzkes models on the one hand, and a percolation model on the other, allowed the origin of electrical resistance changes to be pointed out, respectively for platinum and palladium sensing layers

Electronic and Mechanical Antagonist Effects in Resistive Hydrogen Sensors Based on Pd@Au Core-Shell Nanoparticle Assembles Prepared by Langmuir-Blodgett

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Palladium-silver mesowires for the extended detection of H2.

International audiencePalladium-silver mesowires are prepared by electrochemical decoration of graphite step-edges with a good control of the alloy composition and wire diameter. As-prepared arrays are used for hydrogen sensing and demonstrate extended detection capabilities up to the whole concentration range of H(2) depending on the alloy composition. At low silver content, low hydrogen concentration is detected but the sensing window is narrow because of sensor saturation. The sensing window is advantageously extended to higher hydrogen concentrations for quantitative measurements up to pure H(2) flows with Ag-rich alloys. The mechanism responsible for these behaviors implies the statistical distribution in surface composition rather than the structural characteristics and stability domains of the corresponding hydride phases

Modifications of MXene layers for supercapacitors

International audienceThe re-stacking of Ti3C2Tx-MXene layers has been prevented by using two different approaches: a facile hard templating method and a pore-forming approach. The expanded MXene obtained by using MgO nanoparticles as hard templates displayed an open morphology based on crumpled layers. The corresponding electrode material delivered 180 F g-1 of capacitance at 1 A g-1 and maintained 99 % of its initial capacitance at 5 A g-1 over five thousand charge-discharge cycles. On the other hand, the MXene foam prepared after heating a MXene-urea composite at 550°C, showed numerous macropores on the surface layer and a complex open 3D inner-architecture. Thanks to this foamy porous structure, the binder-free electrode based on the resulting MXene foam displayed a great capacitance of 203 F g-1 at 5 A g-1 current density, 99 % of which was retained after five thousand cycles. In comparison, the pristine MXene-based electrode delivered 82 F g-1 , only, in the same operating conditions. An asymmetric device built on a negative MXene foam electrode and a positive MnO2 electrode exhibited an attractive energy density of 16.5 Wh kg-1 (or 10 Wh L-1) and 160 W kg-1 (or 8.5 kW L-1) power density. Altogether, the enhanced performances of these nano-engineered 2D materials are a clear demonstration of the efficiency of the chosen synthetic approaches to work out the re-stacking issue of MXene layers

Laser‐Induced Colloidal Writing of Organometallic Precursor–Based Repeatable and Fast Pd–Ni Hydrogen Sensor

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New topotactic synthetic route to mesoporous silicon carbide

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Two-Photon Fluorescence Imaging and Therapy of Cancer Cells with Anisotropic Gold-Nanoparticle-Supported Porous Silicon Nanostructures

International audienceIn this work, we prepared porous silicon (pSi) nanostructures decorated with gold nanoparticles, as probes for cell tissue imaging under two‐photon excitation. We also demonstrated that the Au/pSi nanosystems induced cytotoxicity and phototoxicity under two‐photon excitation