Elaboration of Ti-Fe based alloys using ball milling : characterization of their electrochemical hydrogen storage properties

L’hydrogène est la solution potentielle pour réussir la transition énergétique d’un système actuel basé en grande partie sur les combustibles fossiles vers un système non émetteur de gaz toxiques et respectueux de l’environnement. Cependant, le stockage de l’hydrogène est un grand défi qui freine son application pratique dans les différents domaines. Les hydrures métalliques permettent de stocker une grande quantité d’hydrogène de façon réversible dans de bonnes conditions (Température, pression, sécurité…) comparée aux autres modes de stockage (gazeux et liquide). En plus, ces mêmes matériaux sont utilisés comme électrode négative dans les batteries Nickel-Métal Hydrure.Dans la première partie de cette thèse, les alliages Ti-Fe ont été synthétisés parmécanosynthèse pour différents temps de broyage et différents rapports massiquesbilles/poudre. Afin d’optimiser les paramètres d’élaboration, ces alliages ont été caractérisés par différentes techniques telles que la diffraction des rayons X, la microscopie électronique à balayage, la chronopotentiométrie, la chronoampérométrie et la voltamétrie cyclique.Dans une seconde partie, les alliages TiFe+4%MWNTs, TiFe0.95-xMx, TiFe0.90M0.10 etTiFe0.90Mn0.05V0.05 (x=0.05, 0.15) (M : Mn ou V) ont été élaborés selon les paramètres optimaux déterminés précédemment. L’influence de l’additif Nanotubes de Carbone à multiparois (MWNTs), de la substitution partielle du Fe par Mn et/ou V et de l’excès de Titane sur les propriétés structurales, morphologiques et électrochimiques telles que l’activation, la capacité de décharge électrochimique, la réversibilité, la tenue au cyclage, le coefficient de diffusion ont ensuite été étudiés. Les propriétés redox des électrodes, le potentiel de Nernst et la densité du courant d’échange, ont été déterminés, en se basant sur la première loi de Sternet le modèle théorique de Bulter -Volmer.Les résultats électrochimiques obtenus montrent que l’alliage TiFe+4 wt.% MWNTs présente les meilleures performances : une activation rapide (au 1er cycle) et une meilleure capacité maximale de décharge (266 mAh g-1) avec une réversibilité qui reste inchangée.Hydrogen is the potential solution to make a success of the energy transition of a current system basically based on fossil fuels towards a system friendly to environment. However, the storage of hydrogen is a big challenge that hinders its practical application in different areas.. Metal hydrides can store a large amount of hydrogen reversibly under good conditions (temperature, pressure, safety ...) compared to other storage modes (gaseous and liquid). In addition, these same materials are used as negative electrode in Nickel-Metal Hydride batteriesIn the first part of this thesis, Ti-Fe alloys were synthesized using mechanical alloying (MA) under argon atmosphere at room temperature, with different ball to powder weight ratio and at different milling times. In order to determine the optimal parameters of the elaboration the metallic composite were investigated using different techniques such as X-ray diffraction, scanning electron microscopy (EDS support), chronopotentiometry, chronoamperometry and cyclic voltammetry,In the second part, the metallic compounds, TiFe+4%MWNTs, TiFe0.95-xMx, TiFe0.90M0.10 and TiFe0.90Mn0.05V0.05 (x=0.05, 0.15) (M : Mn or V), which are used as the negative electrode material for Ni-MH secondary batteries, were synthesized by mechanical alloying according to optimal parameters, previously determined.The effect of MWNT addition, the Mn and/or V partial substitution for Fe and the excess of titanium on the structural, morphological and electrochemical parameters such as activation, electrochemical discharge capacity, reversibility, cycle life time and hydrogen diffusion coefficient were investigated.The redox properties of the electrodes such as the Nernst potential and the exchange current density were studied based on Stern’s first law and the theoretical model of Bulter-Volmer.The electrochemical properties of studied samples show the best performance for TiFe+4% MWNTs alloy. Indeed, this alloy presents a rapid activation (1st cycle) and a best discharge capacity (266 mAhg-1) with a reversibility remaining unchange

Structure and electrochemical hydrogen storage properties of Ti2Ni alloy synthesized by ball milling

International audienceThe structure and the electrochemical hydrogen storage properties of amorphous Ti2Ni alloy synthesized by ball milling and used as an anode in nickel–metal hydride batteries were studied. Nominal Ti2Ni was synthesized under argon atmosphere at room temperature using a planetary high-energy ball mill. The structural and morphological characterization of the amorphous Ti2Ni alloy is carried out by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The electrochemical characterization of the Ti2Ni electrodes is carried out by the galvanostatic charging and discharging, the constant potential discharge, the open circuit potential and the potentiodynamic polarization techniques.The Ti2Ni alloy activation requires only one cycle of charge and discharge, regardless of the temperature.The electrochemical discharge capacity of the Ti2Ni alloy, during the first eight cycles, and at a temperature of 30 °C, remained practically unchanged and a good held cycling is observed. By increasing the temperature, the electrochemical discharge capacity loss after eight cycles undergoes an increase and it is more pronounced for the temperature 60 °C.At 30 °C, the anodic corrosion current density is 1 mA cm−2 and then it undergoes a rapid drop, remaining substantially constant (0.06 mA cm−2) in the range 40–60 °C, before undergoing a slight increase to 70 °C (0.3 mA cm−2). This variation is in good agreement with the maximum electrochemical discharge capacity values found for the different temperatures.By increasing the temperature, the difference between the OCP curves corresponding to C/10 and C/30 regimes undergoes significant growth, reaching a maximum value (ΔEOCV = 10.3 mV) at 60 °C before undergoing a decrease at 70 °C.A good correlation is found between the evolutions of the corrosion current density with the maximum discharge capacity on one hand and on the other hand with the ΔEOCV, according to the temperature. The effect of temperature on the different electrochemical parameters (Icorr, Cmax, ΔEOCV) and the various correlations found between them allows us to optimize the performance of the battery and provide proper operation under the good experimental conditions

Electrochemical properties of Ti2Ni hydrogen storage alloy

International audienceIn this paper, the long cycling behavior, the kinetic and thermodynamic properties of Ti2Nialloy used as negative electrode in nickel-metal hydride batteries have been studied bydifferent electrochemical techniques. Several methods, such as, galvanostatic charge anddischarge, the constant potential discharge and the potentiodynamic polarization areapplied to characterize electrochemically the studied alloy. The studied electrodes areobserved before and after electrochemical tests at different temperatures by scanningelectron microscopy.The amorphous Ti2Ni is activated after five cycles and the achieved maximumdischarge capacity is about 67 mAh g_1 at ambient temperature. Despite the low values ofthe maximum discharge capacity and the cycling stability (17%) and the steep decrease ofthe discharge capacity after activation, this alloy conserves a good stability lifetime duringa long cycling. A good correlation is observed between the evolution of the discharge capacityand those of the redox parameters during a long cycling.The enthalpy change, the entropy change and the activation energy of the formationreaction of the Ti2Ni metal hydride are evaluated electrochemically. The found values ofthe enthalpy change, the entropy change and the activation energy are about_43.3 kJ mol_1, 51.7 J K_1 mol_1 and 34.9 kJ mol_1, respectively

Corrosion behavior of cold sprayed 7075Al composite coating reinforced with TiB2 nanoparticles

International audienceCold spray (CS), as a novel surface treatment technique, has been widely used for repairing damaged components and as protecting coatings, especially for the applications of aircraft and marine components. To further improve the mechanical properties, while maintaining the corrosion resistance of pure Al and Al alloy coatings, ceramic particles are commonly added into the Al matrix to produce particle-strengthened Al matrix composite (P-AMC) coatings. In this study, dense 7075Al composite coatings reinforced with uniformly distributed in-situ TiB 2 nanoparticles (hereafter named TiB 2 /7075Al) were successfully produced by CS using a gas-atomized composite powder and the propulsive gases of air and helium. Following this, the corrosion behavior of the cold sprayed (CSed) TiB 2 /7075Al composites was investigated using Tafel polarization, electrochemical impedance, spectroscopy, and immersion tests in 0.1 M and 0.6 M NaCl solutions, and were compared to those of the CSed pure 7075Al coating and bulk 7075Al-T6 material. Electrochemical tests revealed that the composite coating exhibits a higher corrosion rate than the pure 7075Al coating, primarily caused by a galvanic coupling between TiB 2 nanoparticles and the more active Al matrix. Compared to the air-processed coatings, the He-processed ones exhibit higher densities of defects, like dislocations, and precipitates due to larger plastic deformation of the sprayed particles, which result in more active sites for corrosion and thus lower corrosion resistance. Lowtemperature annealing treatment (230 °C/6 h) reduces these defects to increase the corrosion resistance of the CSed coatings. Comparatively, high-temperature annealing treatment (412 °C/4 h) results in the coarsening of precipitates and grain growth to increase the corrosion rate of the coatings. Corrosion mechanisms of the CSed and annealed composite coatings related to the microstructure evolution were investigated in detail