Improvement of substituting La with Ce on hydrogen storage thermodynamics and kinetics of Mg-based alloys

Abstract

The rare earth elements are believed to catalyze the reversible reaction between magnesium and hydrogen and reduce the thermal stability of MgH2 by weakening the Mg–H bond. This study focuses on investigating the effect of Ce partial substitution of La on the comprehensive hydrogen storage performances of La10-xCexMg80Ni10 (x = 0–4) alloys (prepared by vacuum induction melting). The phase composition and microstructure were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and high-resolution transmission electron microscopy (HRTEM). The thermodynamics and kinetics of isothermal reactions were measured by the automatic Sievert apparatus. Non-isothermal dehydrogenation performance of the alloys was researched by thermogravimetry analysis (TGA) and differential scanning calorimetry (DSC). All the experimental alloys have a large capacity of hydrogen absorption and desorption and the kinetics of the Ce containing alloys is better. The additive Ce exists in the solid solution of alloy and results in the refinement of grain, making the stability of the hydride visibly lower, which is the reason for the decline in the initial dehydrogenation temperature and enthalpy (ΔH) of the hydride. Besides, the dehydrogenation activation energy of the alloys is distinctly reduced by composition adjustment, which indicates the improved hydrogen storage performances.