Effect of La-Ni@3DG catalyst concentration on the hydrogen storage properties of MgH2

This research paper explores the influence of varying the quantity of La-Ni@3DG catalyst on the hydrogen storage capabilities of MgH2. La-Ni@3DG catalyst was prepared using lanthanum chloride heptahydrate and nickel chloride hexahydrate as raw materials combined with three-dimensional graphene, then mixed with MgH2 via ball milling to prepare MgH2 + x wt.% La-Ni@3DG (x = 0, 3, 5, 7) composite alloy. X-ray diffraction analysis showed that the composite alloy was mainly composed of the MgH2 phase, with the presence of Mg and (La, Ni) phases detected. With increased La-Ni@3DG addition, the broadening of the MgH2 diffraction peak significantly improved, indicating the catalyst promoted alloy phase structure uniformity and crystallinity. The composite alloy forms new phases such as LaH3, LaNi3H6, and Mg2NiH4 during hydrogen absorption. These phases cooperate with in-situ formed LaH3 and Mg2Ni to significantly improve the reversible hydrogen absorption and desorption properties of MgH2. Adding La-Ni@3DG catalyst has a significant positive effect on the hydrogen absorption and desorption of MgH2, leading to a considerable improvement. At 553 K, the composite alloy reaches hydrogen absorption equilibrium faster than pure MgH2, and the temperature for hydrogen absorption is significantly reduced to 373 K. The dehydrogenation performance is also improved, with 5 wt.% La-Ni@3DG is showing the best dehydrogenation performance at 553 K. The initial dehydrogenation temperature commences at approximately 505 K, while the dehydrogenation activation energy attains its minimum value: a remarkably low 109.91 kJ/mol H2. Additionally, the addition of catalyst reduces the pressure of the hydrogen absorption and desorption platform, effectively reducing the hysteresis effect during hydrogen absorption and desorption when the catalyst content is 5 wt.%, the enthalpy change and entropy change of the composite alloy reach a minimum,-70.45 kJ/mol H2 and 74.38 kJ/mol H2 (hydrogen absorption),-101.93 J/K/mol H2 and 103.68 J/K/mol H2 (hydrogen desorption), respectively.