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 MgH 2 . 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 MgH 2 via ball milling to prepare MgH 2  +  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 MgH 2 phase, with the presence of Mg and (La, Ni) phases detected. With increased La–Ni@3DG addition, the broadening of the MgH 2 diffraction peak significantly improved, indicating the catalyst promoted alloy phase structure uniformity and crystallinity. The composite alloy forms new phases such as LaH 3 , LaNi 3 H 6 , and Mg 2 NiH 4 during hydrogen absorption. These phases cooperate with in-situ formed LaH 3 and Mg 2 Ni to significantly improve the reversible hydrogen absorption and desorption properties of MgH 2 . Adding La–Ni@3DG catalyst has a significant positive effect on the hydrogen absorption and desorption of MgH 2 , leading to a considerable improvement. At 553 K, the composite alloy reaches hydrogen absorption equilibrium faster than pure MgH 2 , 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 H 2 . 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 H 2 and 74.38 kJ/mol H 2 (hydrogen absorption), −101.93 J/K/mol H 2 and 103.68 J/K/mol H 2 (hydrogen desorption), respectively.