Étude des propriétés des composés LaNi3.55Mn0.4Al0.3Co0.75-xFex (0 = x = 0.75) (application aux accumulateurs Ni-MH)

Nous avons étudié l'influence de la substitution du cobalt par le fer sur le comportement thermodynamique et électrochimique des hydrures des composés intermétalliques polysubstitués LaNi3.55Mn0.4Al0.3Co0.75-xFex (x = 0, 0.35, 0.75). La substitution partielle du cobalt par le fer permet de conserver une bonne durée de vie des électrodes, par contre la substitution totale entraîne une décroissance rapide de la capacité. Cette décroissance provient de la corrosion de l'alliage qui est attaqué par la potasse au cours du cyclage électrochimique. La décrépitation de l'alliage a été suivie par des mesures de microscopie électronique à balayage. Nous avons aussi établi une méthode originale de caractérisation quantitative de la décomposition de l'alliage en utilisant l'évolution des propriétés magnétiques de ces composés avant et après cyclage électrochimique. Cette méthode nous a permis de calculer le taux de décomposition de l'alliage, le pourcentage, la taille et la nature des particules de métaux de transition (Ni, Co, Fe) ségrégées en surface. Nous avons pu estimer l'épaisseur de la couche de corrosion. Un modèle pour le mécanisme de la corrosion basé sur ces résultats expérimentaux, est proposé afin d'expliquer les différences de comportement observés pour ces matériaux d'électrodes.We have studied the influence of iron substitution for cobalt on the thermodynamic and electrochemical behavior of the hydrides of polysubstituted LaNi 3.55Mn0.4Al0.3Co0.75-x(X = 0, 0.35, 0.75) alloys. Partial iron for cobalt substitution allows to maintain a good cycle life, whereas complete substitution leads to a rapid loss of the capacity. This decrease is due to KOH corrosion during the electrochemical cycling. The decrepitation of the alloys was followed by measurements of electronic scan microscopy. We also established an original method of quantitative characterization of the decomposition of the alloy by using the evolution of the magnetic properties of these compounds before and afier electrochemical cycling. This method enabled us to calculate the rate of the alloy decomposition, the percentage, the size and the nature of the transition metal (Ni,Co,Fe) particles segregated on the surface. We have also estimated the thickness of the corrosion layer. A model for the corrosion mechanism, which is based on these results, is proposed to explain the differences in behavior observed for these electrode materials.PARIS12-CRETEIL BU Multidisc. (940282102) / SudocSudocFranceTunisiaFRT

The electrochemical performance of AB3-type hydrogen storage alloy as anode material for the nickel metal hydride accumulators

"The original publication is available at www.springerlink.com"International audienceFor the purpose of lowering the cost of metal hydride electrode, the La of LaY2Ni9 electrode was replaced by Ce. The electrochemical performances of the CeY2Ni9 negative electrode, at a room and different temperatures, were compared with the parent alloy LaY2Ni9. At room temperature during a long cycling, the evolution of the electrochemical capacity—the diffusivity indicator (DH/a2 )—the exchange current density, and the equilibrium potential were determined. At different temperatures, the electrochemical characterization of this alloy allowed the estimation of the enthalpy, the entropy, and the activation energy of the hydride formation. The evolution of the high-rate dischargeability was also evaluated at different temperatures. Compared with the parent LaY2Ni9 alloy, CeY2Ni9 exhibits an easy activation and good reaction reversibility. This alloy also conserves a good lifetime during a long-term cycling. A lower activation energy determined for this alloy corresponds to an easy absorption of hydrogen into thisnew alloy

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

Structural, morphological, and electrochemical properties of AB5 hydrogen storage alloy by mechanical alloying

International audienceMechanical alloying (MA) is one of the most promising methods in the development of intermetallic alloys and their scientific research. In this paper, elemental powder mixtures of Ca, Ni, and Mn of nominal composition CaNi5-xMnx (with x =0.3, 0.5, and 1) were elaborated by MA technique during different milling times (2–60 h). Structural, morphological, and electrochemical changes were investigated by X-ray diffraction (XRD), scanning electron microscopy, and Ec-Lab galvanostat, respectively. The XRD test indicated that each alloy has Ni and CaNi3 or CaNi5 phases. In addition, the particle size of the ground powders is decreased with increasing milling time. Furthermore, all alloys have a very high activation capacity, whereby the activation capacity can be fully realized during the first cycle. The results showed that the most significant value of discharge capacity for all alloys was 40 h

Electrochemical properties of the CaNi 4 . 8 M 0.2 (M=Mg, Zn, and Mn) mechanical milling alloys used as anode materials in nickel‐metal hydride batteries

International audienceAbstract The present research work examines the electrochemical properties of CaNi 4.8 M 0.2 (M=Mg, Zn) type alloy applied as an anode in nickel metal hybrid batteries. Based on an extensive study of the CaNi 4.8 Mn 0.2 compound prepared by mecano‐synthesis; under an argon atmosphere, with a variation of milling time and weigh ratio, using a Retsch PM400 type ball mill. The experimental results show that the excellent electrochemical properties were obtained for a milling time of 40 h and a ball‐to‐powder weight ratio equal to 8:1. Based on this study, we examined electrochemically the CaNi 4.8 M 0.2 (M=Mg, Zn, and Mn) compound according to the optimized parameters. Several methods, such as galvanostatic polarization and potentiodynamic polarization, were applied to characterize these electrodes. CaNi 4.8 M 0.2 (M=Mg, Zn, and Mn) electrodes were activated, respectively, during the first, second, and third cycles. The maximum discharge capacity was about 87, 60, and 96 mAhg −1 at ambient temperature. These electrochemical findings correlate with the kinetic results provided during a long cycle

Phase structure and electrochemical characteristics of CaNi4.7Mn0.3 hydrogen storage alloy by mechanical alloying

International audienceIn this paper, we study systematically the effect of ball/powder weight ratio on the morphological, structural, and electrochemical properties of CaNi4.7Mn0.3 powder alloy by mechanical milling. The CaNi4.7Mn0.3 alloy powder is elaborated for an optimal milling time of 40 h with 8:1 and 12:1 ball/powder weight ratios. The X-ray diffraction (XRD) characterization shows that the CaNi4.7Mn0.3 alloy powder is characterized by a nanocrystalline/amorphous crystallographic state and exhibits two major Ni and CaNi3 phases irrespective of the ball/powder weight ratio. The CaNi4.7Mn0.3 electrode activates rapidly in the first cycle regardless of the ball/powder weight ratio, and the best value of maximum discharge capacity is obtained for an 8:1 ratio (125 mAh g−1). The values of diffusion coefficient/mean grain size squared ratio DHa2, Nernst’s potential E0, and exchange current density I0 at the first activation cycle are the best for 8:1 ball/powder weight ratio. After activation, the discharge capacity decreases exponentially regardless of the ball/powder weight ratio. Indeed, the capacity loss and the degradation rate after 50th cycle are about 71%, 10.71 cycle−1 and 53%, 2.95 cycle−1 for 8:1 and 12:1, respectively. The evolution of the DHa2 ratio, E0, and I0 during the cycling is in good agreement with that of the discharge capacity. The highest values of the diffusion coefficient DH, Nernst’s potential E0, and exchange current density I0 after 50th cycle are observed for 8:1 ball/powder weight ratio

Electrochemical Studies on the Ca‑Based Hydrogen Storage Alloy for Different Milling Times

International audienceThe ­CaNi 4.8 Mn 0.2 powder was synthesized by mechanical alloying, under an atmosphere of argon at room temperature,<br&gtat different milling times (2, 10, 20, 30, 40, 50 and 60 h) with ball to powder weight ratio of 8:1. The structural and morphological characterizations of the ­CaNi 4.8 Mn 0.2 powder were carried, respectively, by scanning electron microscopy and X-ray diffraction. After 2 h, all the alloys had a biphasic structure, two major phases, Ni and Ca 2 Ni 7 , remained virtually unchanged when a small amount of Mn was added. After more than 40 h of milling, the same peaks of the Ni and ­Ca 2 Ni 7 phases appeared, while the intensity of the peaks decreased, indicating an additional amorphization process. After 50 h of milling, this damping was followed by the crystallization amorphization. The electrochemical properties of ­CaNi 4.8 Mn 0.2 electrodes were studied at different milling times (10, 20, 30, 40, 50 and 60 h) and in KOH electrolyte concentrations (1 M and 6 M) at ambient temperature, as anodes in the Ni–MH battery. Different techniques were used, such as galvanostatic polarization, potentiostatic polarization and potentiodynamic polarization

Electrochemical study of LaGaO3 as novel electrode material of hydrogen battery (Ni/MH)

International audienceThe physico-chemical performance of the novel anode LaGaO3 forNi/MH accumulators was studied using the electrochemical impedancespectroscopy (EIS) method during cycling. The measured EIS data ofthe perovskite oxide are fitted according to the proposedequivalent circuit representing various processes involved in themechanism of hydrogenation/dehydrogenation reactions of the oxide.Different kinetic elements such as current density I0, chargetransfer resistance Rct, hydrogen transfer resistance Rht, doublelayer capacitance Cdl, and mass hydrogen diffusion Y0 wereestimated under cycling. The EIS results relieved that currentdensity I0 of the oxide increases quickly during the activationprocess and its maximum value is obtained at the second cycle(377.67 mA g_1). The degradation of the charge transfer rate of theoxide after activation can be ascribed to the corrosion of theelectrode/electrolyteinterface. The variation of the Warburgimpedance Y0 could be attributed to the change in the morphologicaland the structure of the working electrode over cycling. The EISanalysis relieved that electrochemical behavior of the oxide iscontrolled by the charge-transfer rate and the modification of theelectrode surface