Hydrogen Gas Phase and Electrochemical Hydriding of LaNi5−xMx (M = Sn, Co, Al) Alloys

Hydriding/dehydriding properties of a series of LaNi5 based alloys were compared by applying both hydrogen gas phase and electrochemical hydrogen charge/discharge methods. The highest hydrogen absorption capacity of 1.4 wt.% H2 was found for LaNi4.3Co0.4Al0.3, although LaNi4.8Sn0.2 also reveals comparable hydrogen capacity (>1.3%). A significant difference in the hydriding kinetics was observed for all studied alloys before and after activation. The activated alloys (5 cycles at 65 °C, 40 atm. H2) reach their maximum capacities after less than a minute, whereas the pure LaNi5 alloy needs several minutes for complete hydriding. The electrochemical hydriding/dehydriding behavior of the alloys reveals superior performance of LaNi4.3Co0.4Al0.3 and LaNi4.8Sn0.2 compared to the other compositions studied, as the capacity of LaNi4.8Sn0.2 decreases by only 10% for 60 charge/discharge cycles at a current density of 100 mA/g. Good agreement between the hydrogen sorption kinetics of the alloys obtained electrochemically and from hydrogen gas phase has also been observed.

The Influence of Cerium on the Hydrogen Storage Properties of La1-xCexNi5 Alloys

La1-xCexNi5 alloys (x = 0, 0.09, 0.25 and 0.5) were investigated in terms of their structures, phase contents, hydrogen storage properties and microhardness. It was confirmed that a cerium addition to the reference (LaNi5) alloy caused structural changes such as lattice shrinkage and, as a result, changed both the absorption and desorption pressures and the enthalpies of formation and decomposition. The alloy with the highest cerium content was found to possess a two-phase structure, probably as a result of nonequilibrium cooling conditions during its manufacturing process. The microhardness was found to increase to some extent with the cerium content and decrease for samples with the highest cerium content.

Activation and Disproportionation of Zr2Fe Alloy as Hydrogen Storage Material

As a hydrogen storage material, Zr2Fe alloy has many advantages such as fast hydrogen absorption speed, high tritium recovery efficiency, strong anti-pulverization ability, and difficulty self-igniting in air. Zr2Fe alloy has lower hydrogen absorption pressure at room temperature than LaNi5 alloy. Compared with the ZrVFe alloy, the hydrogen release temperature of Zr2Fe is lower so that the material can recover hydrogen isotopes at lower hydrogen concentration efficiently. Unfortunately, the main problem of Zr2Fe alloy in application is that a disproportionation reaction is easy to occur after hydrogen absorption at high temperature. At present, there is little research on the generation and influencing factors of a disproportionation reaction in Zr2Fe alloy. In this paper, the effects of temperature and hydrogen pressure on the disproportionation of Zr2Fe alloy were studied systematically. The specific activation conditions and experimental parameters for reducing alloy disproportionation are given, which provide a reference for the specific application of Zr2Fe alloy.

Investigation on the thermodynamic analysis, preparation and characterization of LaNi5 - hydrogen storage alloy by magnesiothermic reduction diffusion process

The present investigation focuses on the preparation of LaNi5 intermetallic compound by ?Metallothermic reduction diffusion process?. Experiments were carried out using oxides and chlorides of La and Ni metal powders as the raw materials with granular Mg powder as the reductant. The thermal reduction process was carried out at 900 ?C for 9 hrs in Ar atmosphere. After the completion of reaction, the contents were purified by treating with dilute acetic acid followed by de-ionized water. Thermodynamic feasibility studies were carried out to determine the probabilistic nature of formation of the desired compound. Thermal analysis was carried out to find the dissociation and decomposition temperature of the reactants. The phase purity and the elemental composition of the alloy were assessed by XRD and EDX analyses. The morphological features of the prepared powders were examined by SEM. From this study, it has been concluded that LaNi5 alloy can be prepared with an appreciable purity by the Metallothermic reduction diffusion process.

Hydriding kinetics of LaNi5 using Nucleation-growth and Diffusion Models

In this paper, the hydriding kinetics of a LaNi5 alloy have been measured with a thermo-gravimetric system. The rate controlling steps have been analyzed. In the α + β phase, a first order Johnson-Mehl-Avrami model provides a good agreement with the measurements. In the ? phase, the previous approach shows that the reaction becomes progressively controlled by the diffusion of hydrogen atoms through the hydride. In order to support this hypothesis, a Crank-Nicholson diffusion model has also been applied and achieved good results. The results show that the transition in the rate controlling mechanism takes place before the static pressure-composition isotherms are reached.