Highly ameliorated gaseous and electrochemical hydrogen storage dynamics of nanocrystalline and amorphous LaMg₁₂-type alloys prepared by mechanical milling

Abstract

Nanocrystalline and amorphous LaMg₁₂-type alloy-Ni composites with a nominal composition of LaMg₁₁Ni+x wt. % Ni (x = 100, 200) were synthesized via ball milling. The influences of ball milling duration and Ni adding amount x on the gaseous and electrochemical hydrogen storage dynamics of the alloys were systematically studied. Gaseous hydrogen storage performances were studied by a differential scanning calorimeter and a Sievert apparatus. The dehydrogenation activation energy of the alloy hydrides was evaluated by Kissinger method. The electrochemical hydrogen storage dynamics of the alloys was investigated by an automatic galvanostatic system. The H atom diffusion and apparent activation enthalpy of the alloys were calculated. The results demonstrate that a variation in Ni content remarkably enhances the gaseous and electrochemical hydrogen storage dynamics performance of the alloys. The gaseous hydriding rate and high-rate discharge (HRD) ability of the alloys exhibit maximum values with varying milling duration. However, the dehydriding kinetics of the alloys is always accelerated by prolonging milling duration. Specifically, rising milling time from 5 to 60 h makes the hydrogen desorption ratio (a ratio of the dehydrogenation amount in 20 min to the saturated hydrogenation amount) increase from 57% to 66% for x = 100 alloy and from 57% to 70% for x = 200. Moreover, the improvement of gaseous hydrogen storage kinetics is attributed to the descending of dehydrogenation activation energy caused by the prolonging of milling duration and growing of Ni content.