Effects of Ni Content and Ball Milling Time on the Hydrogen Storage Thermodynamics and Kinetics Performances of La–Mg–Ni Ternary Alloys

The effects of Ni content and ball milling time on the hydrogen storage thermodynamics and kinetics performances of as-milled La5Mg95-xNixx=5,10,15\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\text{La}}_{5} {\text{Mg}}_{95 - x} {\text{Ni}}_{x} \left( {x = 5, \, 10, \, 15} \right)$$\end{document} ternary alloys have been investigated. The evolution of microstructure and phase of experimental alloys in the absorption/desorption process has been characterized by XRD, SEM and HRTEM. The hydrogen storage kinetics and thermodynamics performances and PCI curves have been tested using the Sievert apparatus. It is found that the rising of Ni content remarkably improves the hydrogen storage kinetic performance, but reduces hydrogen storage capacity. And with the increase in milling time, hydrogen desorption activation (Ea) value decreases firstly and then increases; the minimum value is 47.6 kJ/mol, and the corresponding milling time is 10 h for La5Mg85Ni10 alloy. As for the thermodynamics properties, the hydrogenation enthalpy (ΔH) and hydrogenation entropy (ΔS) both decrease firstly and then increase with the rising of Ni content and milling time. The composite La5Mg85Ni10 alloy milled for 10 h exhibits the best thermodynamics and kinetics performances, the lowest Ea of 47.6 kJ/mol, absorption of 5.4 wt.% within 5 min and desorption of 5.2 wt.% within 3 min at 360 °C and the lowest ΔH and ΔS of 72.1 kJ/mol and 123.2 J/mol/K.