Hydrogen storage thermodynamics and dynamics of La–Mg–Ni-based LaMg₁₂-type alloys synthesized by mechanical milling

Abstract

Nanocrystalline/amorphous LaMg₁₂-type alloy–Ni composites with a nominal composition of LaMg₁₁Ni + x wt% Ni (x = 100, 200) were synthesized by mechanical milling. Effects of Ni content and milling time on the gaseous hydrogen storage thermodynamics and dynamics of alloys were systematically investigated. The hydrogen desorption properties were studied by Sievert apparatus and a differential scanning calorimeter (DSC). Thermodynamic parameters (ΔH and ΔS) for the hydrogen absorption and desorption of alloys were calculated by Van’t Hoff equation. Hydrogen desorption activation energy of alloy hydride was estimated by Arrhenius and Kissinger methods. The increase in Ni content has a slight effect on the thermodynamic properties of alloys, but it significantly enhances the hydrogen absorption and desorption kinetics performance of alloys. Moreover, variation of milling time clearly affects the hydrogen storage properties of alloys. Hydrogen absorption capacity ($C_{ 1 0 0}^{\text{a}}$) and hydrogen absorption saturation ratio ($R_{ 1 0}^{\text{a}}$) (a ratio of the hydrogen absorption capacity at 10 min to the saturated hydrogen absorption capacity) have maximum values with milling time varying. But hydrogen desorption ratio ($R_{ 2 0}^{\text{d}}$) (a ratio of the hydrogen desorption capacity at 20 min to the saturated hydrogen absorption capacity) always increases with milling time prolonging. Particularly, prolonging milling time from 5 to 60 h makes $R_{ 2 0}^{\text{d}}$ increase from 10.89% to 16.36% for the x = 100 alloy and from 13.93% to 21.68% for the x = 200 alloy, respectively.