Search

The present work gives the electronic structures of La 3-x Mg x Ni 9 (x = 0.0–2.0) alloys by first-principles calculations using the generalized gradient approximation of Perdew-Wang 91 (GGA-PW91) method within Cambridge Serial Total Energy Package (CASTEP), aiming at gaining insight into the hydrogen storage mechanism of La 3-x Mg x Ni 9 alloys modified by Mg. The results show that the La 3-x Mg x Ni 9 alloys consist predominantly of interactions between La-Ni, Ni-Ni or/and Mg-Ni. Among them, La-Ni interaction is the major factor controlling the structural stability of the alloys. Mg substitution increases the La-Ni bonding interactions to achieve stable Mg-containing metal matrices for reversible hydrogen absorption-desorption. This is particularly obvious at high Mg composition, as the La-Ni interactions gradually increase with Mg content. The increase of La-Ni interactions coupled with the decrease of Mg-Ni and Ni-Ni interactions will relieve the hydrogen-induced amorphization and disproportionation, and subsequently enhance the cyclic stability of La 3-x Mg x Ni 9 alloys at high Mg content. However, Mg substitution for La leads to a subsequent contraction in cell volume, dramatically reducing the reversible H capacity at high Mg composition such as LaMg 2 Ni 9. Suitable Mg content in La-Mg-Ni systems, such as an approximately range x = 1.0–1.4 in La 3-x Mg x Ni 9 alloys, is required in trade-off between hydrogen storage capacity and cycle life. • La 3-x Mg x Ni 9 (x = 0–2) alloys with defined La and Mg atoms are introduced for calculation. • Mg substitution leads to a gradual contraction in cell volume for less H-capacity. • La-Ni interaction is dominant in the structural stability of La 3-x Mg x Ni 9 alloys. • Increased La-Ni and decreased Mg/Ni-Ni interactions favor for cycle stability. [ABSTRACT FROM AUTHOR]

The La–Mg–Ni–Co-based AB 2 -type alloys, namely La 0.7 Sm 0.3 MgNi 3·6 Co 0.4 x wt.%Ni (x = 0,5,10, 15, 20), were synthesized through ball milling. The study focused on investigating the impact of Ni content on the structures and electrochemical properties. The structures of the samples were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM) and Transmission electron microscope (TEM). It has been demonstrated that the experimental samples consist of a primary phase, LaMgNi 4 , and a secondary phase, LaNi 5. The abundance of phases undergoes significant changes with variations in Ni content, while the phase composition remains constant. The results indicate that a rise in Ni concentration results in an elevation of the LaNi 5 phase and a reduction of the LaMgNi 4 phase. Additionally, ball milling and the addition of nickel contribute to the refinement of the alloy grains. As the nickel concentration reached 20 wt%, the cycle retention rate(S 30) of the composite alloy electrode achieved its maximum value of 73.42 %. In addition, the electrochemical kinetic test findings demonstrated that the maximum D value of the hydrogen diffusion system was 1.807 × 10−10 cm2/s and that the maximum current density of the composite hydrogen storage alloy electrode was 723 mA/g when x = 0 wt%. The La–Mg–Ni–Co-based AB 2 -type alloys, namely La 0.7 Sm 0.3 MgNi 3·6 Co 0.4 x wt.%Ni (x = 0,5,10, 15, 20), were synthesized through ball milling. The study focused on investigating the impact of Ni content on the structures and electrochemical properties. The structures of the samples were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM) and Transmission electron microscope (TEM). It has been demonstrated that the experimental samples consist of a primary phase, LaMgNi 4 , and a secondary phase, LaNi 5. The abundance of phases undergoes significant changes with variations in Ni content, while the phase composition remains constant. The results indicate that a rise in Ni concentration results in an elevation of the LaNi 5 phase and a reduction of the LaMgNi 4 phase. Additionally, ball milling and the addition of nickel contribute to the refinement of the alloy grains. As the nickel concentration reached 20 wt%, the cycle retention rate(S 30) of the composite alloy electrode achieved its maximum value of 73.42 %. In addition, the electrochemical kinetic test findings demonstrated that the maximum D value of the hydrogen diffusion system was 1.807 × 10−10 cm2/s and that the maximum current density of the composite hydrogen storage alloy electrode was 723 mA/g when x = 0 wt%. [Display omitted] • The mechanism of the effect of microstructure on electrochemical performance was explored. • The capacity fading mechanism of ball milling on RE-Mg-Ni-based alloys was explored. • The comprehensive electrochemical properties of RE-Mg-Ni-based alloys are improved. [ABSTRACT FROM AUTHOR]

Hydrogen storage alloys of La 2- x Y x Mg 16 Ni (x = 0, 0.1, 0.2, 0.3, 0.4) were smelted by vacuum induction melting furnace. The microstructure of the cast alloys were observed by scanning electron microscope, and the alloys structure were analyzed by X-ray Diffractometer (XRD) before and after hydrogen absorption. The electrochemical capacity, cyclic stability, high-rate discharge, potentiodynamic polarization curves, and constant potential crossing curves were tested. Besides, the limited current density and diffusion coefficient were calculated. The results show that the main phase of the as-cast alloy is La 2 Mg 17 , and a little amount of the second phase Mg 2 Ni exist. In addition, LaH 3 and MgH 2 and a small amount of Mg 2 NiH 4 phases were formed in the alloy after saturated hydrogen absorption. With the increasing of La element substituted by Y element in La 2 Mg 16 Ni alloy, the discharge specific capacity of alloy shows a decreasing tendency, it's unconspicuous, though. The cyclic stability and high rate discharge of hydrogen storage alloys increase first and then decrease with the increasing of La element substituted by Y element in La 2 Mg 16 Ni alloy. When S 50 is 34.01%, the cyclic stability of La 1.8 Y 0.2 Mg 16 Ni alloy is best. Both the limited discharge current density and hydrogen diffusion coefficient of the alloy increase first and then decrease with the increasing of the La element of La 2 Mg 16 Ni alloy replaced by Y element. The maximum current density of La 1.8 Y 0.2 Mg 16 Ni alloy is I L = 325.11 mA/g, and the maximum diffusion coefficient is D = 1.849 × 10−8 cm2/s. • The main phase of the as-cast alloy is La 2 Mg 17 , and the second phase Mg 2 Ni exist. • With the increasing of La, the discharge specific capacity shows a decreasing tendency. • La 1.8 Y 0.2 Mg 16 Ni alloy has the best cycle stability (S 50 = 34.01%). • The maximum current density and diffusion coefficient are 325.11 mA/g and 1.849 × 10−8 cm2/s. [ABSTRACT FROM AUTHOR]