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

Allelopathic Effects of Aqueous Extracts of Eucalyptus occidentalis, Acacia ampliceps and Prosopis juliflora on the Germination of Three Cultivated Species

This study concerns the effect of the aqueous extracts of Eucalyptus occidentalis, Acacia ampliceps and Prosopis juliflora on the germination of three species frequently cultivated in the South of Tunisia: Barley (Hordeum vulgare), annual lucerne (Medicago sativa) and jew's mallow (Corchorus olitorius). Aqueous extracts were obtained after a maceration of the dry plant material in distilled water (90 g/l) during 48 h at 60°C. The extraction was made from three vegetative organs (roots, twigs and leaves) for each species. The results showed a variable behavior between the species according to the origin of the extract. Barley is the most sensitive species, showing decrease of germination rate essentially with the leaf extracts of P. juliflora (52.5 ± 15.86%), E. occidentalis (61.5 ± 7.89%) and A. ampliceps (65.5 ± 5.7%). The annual lucerne showed a moderate tolerance; its germination rate was 76 ± 11.61, 81.5 ± 5.74 and 96 ± 2.82%, respectively, for the leaf extracts of A. ampliceps, E. occidentalis and P. juliflora. C. olitorius was found to be the most tolerant species to all extracts; only leaf extracts of E. occidentalis resulted in a lower germination than the control; it was 90 ± 4.32%. The extracts of the studied species affected the root system length; a reduction of the length was essentially observed for M. sativa and C. olitorius

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

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 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

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

Kinetic and thermodynamic studies of hydrogen storage alloys as negative electrode materials for Ni/MH batteries: a review

International audienceThis paper reviews the present performances ofintermetallic compound families as materials for negativeelectrodes of rechargeable Ni/MH batteries. The performanceof the metal-hydride electrode is determined by both thekinetics of the processes occurring at the metal/solutioninterface and the rate of hydrogen diffusion within the bulkof the alloy. Thermodynamic and electrochemical propertiesfor each hydride compound family will be reported. The stepsof hydrogen absorption/desorption such as charge-transferand hydrogen diffusion for evaluating the electrochemicalproperties of hydrogen storage alloys are discussed. Exchangecurrent density (I 0) and hydrogen diffusion coefficient (DH)are the two most important parameters for evaluating theelectrochemical properties of metal hydride electrode. Thevalues of the two parameters for a number of hydrogen storagealloys are compared. The relationship between alloycomposition and electrochemical properties is noted andevaluated