Hongwei Shang

Structure and electrochemical hydrogen storage characteristics of the as-cast and annealed La0.8-xSmxMg0.2Ni3.15Co0.2Al0.1Si0.05 (x=0-0.4) alloys

Abstract In order to ameliorate the electrochemical cycle stability of the RE-Mg-Ni based A 2 B 7 -type electrode alloys, the Mg content in the alloy was reduced and La in the alloy was partially substituted by Sm. The La 0.8- x Sm x Mg 0.2 Ni 3.15 Co 0.2 Al 0.1 Si 0.05 ( x =0, 0.1, 0.2, 0.3, 0.4) electrode alloys were fabricated by casting and annealing. The microstructures of the as-cast and annealed alloys were characterized by XRD and SEM. The electrochemical hydrogen storage characteristics of the as-cast and annealed alloys were measured. The results revealed that all of the experimental alloys mainly consisted of two phases: (La, Mg) 2 Ni 7 phase with the hexagonal Ce 2 Ni 7 -type structure and LaNi 5 phase with the hexagonal CaCu 5 -type structure. As Sm content grew from 0 to 0.4, the discharge capacity and the high rate discharge ability (HRD) first increased and then decreased for the as-cast and annealed alloys, whereas the capacity retaining rate ( S 100 ) after 100 cycles increased continuously.

Gaseous and electrochemical hydrogen storage kinetics of as-quenched nanocrystalline and amorphous Mg2Ni-type alloys

The nanocrystalline and amorphous Mg2Ni-type Mg2Ni1−xCox (x = 0, 0.1, 0.2, 0.3, 0.4) alloys were synthesized by melt quenching technology. The structures of the as-cast and quenched alloys were characterized by XRD, SEM and HRTEM. The gaseous hydrogen storage kinetics of the alloys was measured using an automatically controlled Sieverts apparatus. The alloy electrodes were charged and discharged with a constant current density in order to investigate the electrochemical hydrogen storage kinetics of the alloys. The results demonstrate that the substitution of Co for Ni results in the formation of secondary phases MgCo2 and Mg instead of altering the major phase Mg2Ni. No amorphous phase is detected in the as-quenched Cofree alloy, however, a certain amount of amorphous phase is clearly found in the as-quenched alloys substituted by Co. Furthermore, both the rapid quenching and the Co substitution significantly improve the gaseous and electrochemical hydrogen storage kinetics of the alloys, for which the notable increase of the hydrogen diffusion coefficient (D) along with the limiting current density (IL) and the obvious decline of the electrochemical impedance generated by both the Co substitution and the rapid quenching are basically responsible.

Hydrogen storage thermodynamic and kinetic characteristics of PrMg12-type alloys synthesized by mechanical milling

To improve the hydrogen storage performance of PrMg12-type alloys, Ni was adopted to replace partially Mg in the alloys. The PrMg11Ni+x wt. % Ni (x = 100, 200) alloys were prepared via mechanical milling. The phase structures and morphology of the experimental alloys were investigated by X-ray diffraction and transmission electron microscopy. The results show that increasing milling time and Ni content accelerate the formation of nanocrystalline and amorphous structure. The gaseous hydrogen storage properties of the experimental alloys were determined by differential scanning calorimetry (DSC) and Sievert apparatus. In addition, increasing milling time makes the hydrogenation rates of the alloys augment firstly and decline subsequently and the dehydrogenation rate always increases. The maximum capacity is 5.572 wt. % for the x = 100 alloy and 5.829 wt. % for the x = 200 alloy, respectively. The enthalpy change (ΔH), entropy change (ΔS) and the dehydrogenation activation energy (

Structures and electrochemical performances of as-cast and spun RE-Mg-Ni-Mn-based alloys applied to Ni-MH battery

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Structures and Electrochemical Performances of As-spun RE-Mg-Ni-Mn-based Alloys Applied to Ni-MH Battery

) markedly lower with increasing the milling time and the Ni content due to the generation of nanocrystalline and amorphous structure.

An Investigation on Hydrogen Storage Kinetics of the Nanocrystalline and Amorphous LaMg12-type Alloys Synthesized by Mechanical Milling

The RE-Mg-Ni-Mn-based AB2-type La1−xCexMgNi3.5Mn0.5(x = 0−0.4) alloys were prepared by spinning treatment. For obtaining the optimum performance, the effects of Ce content and spinning rate on the hydrogen storage performance of the alloys were studied systematically. The results show that the variations of the spinning rate and Ce content result in noteworthy changes of the phase content without altering phase composition of the alloys. Specifically, the LaMgNi4 phase increases and LaNi5 phase decreases when increasing the spinning rate and Ce content. Furthermore, the crystalline grains of Ce-containing alloys prepared by spinning treatment are remarkably refined. The alloys own superior electrochemical performance. All alloys reach the optimal discharge capacity at the initial cycle. Increasing Ce content and spinning rate lead the discharge capacity and electrochemical kinetics rise to an optimal value and then start to reduce. Meanwhile, the electrochemical cycle stability is also improved, which is ascribed to the great enhancement of anti-pulverization and anti-corrosion abilities resulting from the spinning treatment and the substitution of Ce for La.

The Preparation and Hydrogen Storage Performances of Nanocrystalline and Amorphous Mg2Ni-Type Alloys

The La-Mg-Ni-Mn-based AB2-type La1-xCexMgNi3.5Mn0.5 (x = 0, 0.1, 0.2, 0.3, and 0.4) alloys were fabricated by melt spinning technology. The effects of Ce content on the structures and electrochemical hydrogen storage performances of the alloys were studied systematically. The XRD and SEM analyses proved that the experimental alloys consist of a major phase LaMgNi4 and a secondary phase LaNi5. The variation of Ce content causes an obvious change in the phase abundance of the alloys without changing the phase composition. Namely, with the increase of Ce content, the LaMgNi4 phase augments and the LaNi5 phase declines. The lattice constants and cell volumes of the alloys clearly shrink with increasing Ce content. Moreover, the Ce substitution for La results in the grains of the alloys clearly refined. The electrochemical tests showed that the substitution of Ce for La obviously improves the cycle stability of the as-spun alloys. The analyses on the capacity degradation mechanism demonstrate that the improvement can be attributed to the ameliorated anti-corrosion and anti-oxidation ability originating from substituting partial La with Ce. The as-spun alloys exhibit excellent activation capability, reaching the maximum discharge capacities just at the first cycling without any activation treatment. The substitution of Ce for La evidently improves the discharge potential characteristics of the as-spun alloys. The discharge capacity of the alloys first increases and then decreases with growing Ce content. Furthermore, a similar trend also exists in the electrochemical kinetics of the alloys, including the high rate discharge ability (HRD), hydrogen diffusion coefficient (D), limiting current density (IL) and charge transfer rate.

Structure, hydrogen storage kinetics and thermodynamics of Mg-base Sm5Mg41 alloy

Nanocrystalline and amorphous LaMg12-type LaMg11Ni + x wt% Ni (x = 100, 200) alloys were synthesized by mechanical milling. Effects of Ni content and milling time on the gaseous and electrochemical hydrogen storage kinetics of as-milled alloys were investigated systematically. The electrochemical hydrogen storage properties of the as-milled alloys were tested by an automatic galvanostatic system. And the gaseous hydrogen storage properties were investigated by Sievert apparatus and a differential scanning calorimeter (DSC) connected with a H2 detector. Hydrogen desorption activation energy of alloy hydrides was estimated by using Arrhenius and Kissinger methods. It is found that the increase of Ni content significantly improves the gaseous and electrochemical hydrogen storage kinetic performances of as-milled alloys. Furthermore, as ball milling time changes, the maximum of both high rate discharge ability (HRD) and the gaseous hydriding rate of as-milled alloys can be obtained. But the hydrogen desorption kinetics of alloys always increases with the extending of milling time. Moreover, the improved gaseous hydrogen storage kinetics of alloys are ascribed to a decrease in the hydrogen desorption activation energy caused by increasing Ni content and milling time.

Comparative study of electrochemical performances of the as-melt Mg20Ni10-xMx (M = None, Cu, Co, Mn; x=0, 4) alloys applied to Ni/metal hydride (MH) battery

© 2012 Zhang et al., licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The Preparation and Hydrogen Storage Performances of Nanocrystalline and Amorphous Mg2Ni-Type Alloys