Microstructure characteristics, dynamic kinetics and thermal properties of Mg77+xNi20-xCe3 (x=0, 5, 10, 15) hydrogen storage alloys

Utilizing element substitution to enhance the hydrogen storage capabilities of Mg-based alloys represents a promising approach in the quest for efficient energy storage solutions. Thereby, in this paper, Ni is chosen to substitute a portion of Mg in a Ce-Mg-based alloy aimed at improving its hydriding and dehydriding performance. Mg77+xNi20-xCe3 (x = 0, 5, 10, 15) alloys are successfully prepared by the vacuum induction melting method. The structural characterizations of the alloys are performed using X-ray diffraction and scanning electron microscope. The alloys are composed of a primary phase of Mg2Ni, lamella eutectic composites of Mg + Mg2Ni, and some amount of CeMg12 and Ce2Mg17. In the as-cast Mg87Ni10Ce3 alloy, the Mg2Ni phase disappears, transforming into a typical eutectic structure of hundreds of nanometers thick Mg-Mg2Ni lamellas. This structure significantly enhances the hydrogen storage kinetics, with a hydrogen absorption capacity of 5.66 wt% at 653 K and a desorption capacity of 5.45 wt% over 2 h at 683 K, outperforming other alloys. Moreover, its peak hydrogen release temperature is significantly lower than that of the Mg92Ni5Ce3 alloy. The formation of the CeH2.29 phase within the alloy acts as a catalyst, effectively improving the exothermic and endothermic kinetics of hydrogen absorption and desorption, resulting in a much lower hydrogen desorption activation energy compared to MgH2. However, the variation in the activation energy of the alloy remains limited, ranging between 66.6 similar to 71.1 kJ/mol.