Hydrogen storage behavior of nanocrystalline and amorphous Mg–Ni–Cu–La alloys

Abstract

Alloying and structural modification are two effective ways to enhance the hydrogen storage kinetics and decrease the thermal stability of Mg and Mg-based alloys. In order to enhance the characteristics of Mg₂Ni-type alloys, Cu and La were added to an Mg₂Ni-type alloy, and the sample alloys (Mg₂₄Ni₁₀Cu₂)_100−xLa_x (x = 0, 5, 10, 15, 20) were prepared by melt spinning. The influences of La content and spinning rate on the gaseous and electrochemical hydrogen storage properties of the sample alloys were explored in detail. The structural identification carried out by XRD and TEM indicates that the main phase of the alloys is Mg₂Ni and the addition of La results in the formation of the secondary phases LaMg₃ and La₂Mg₁₇. The as-spun alloys have amorphous and nanocrystalline structures, and the addition of La promotes glass formation. The electrochemical properties examined by an automatic galvanostatic system show that the samples possess a good activation capability and achieve their maximal discharge capacities within three cycles. The discharge potential characteristics were vastly ameliorated by melt spinning and La addition. The discharge capacities of the samples achieve their maximal values as the La content changes, and the discharge capacities always increase with increasing spinning rate. The addition of La leads to a decline in hydrogen absorption capacity, but it can effectively enhance the rate of hydrogen absorption. The addition of La and melt spinning significantly increase the hydrogen desorption rate due to the reduced activation energy.