Introducing Ni-N-C ternary nanocomposite as an active material to enhance the hydrogen storage properties of MgH2

The use of Mg-based materials as solid-state hydrogen storage materials can provide a viable solution to the bottleneck hindering the development of hydrogen energy. However, it is necessary to address their excessively stable thermodynamic properties and sluggish kinetic performances. In this study, we prepared a Ni-N-C ternary nanocomposite (designated as Ni@NC) catalyst using Ni-based metal-organic frameworks (Ni-MOFs) as a precursor for catalytic MgH2 hydrogen storage properties. The Ni@NC catalyst exhibited excellent promotion effects on the hydrogen absorption and desorption kinetics and the cycling stability of the Mg-based materials. Notably, the composite exhibited room-temperature hydrogen absorption initiation and an onset dehydrogenation temperature of 188°C, with complete hydrogenation achieved after holding at 100°C for 60 min. After undergoing 100 cycles of absorption/dehydrogenation, the capacity retention rate was 99.5%. The differential scanning calorimetry (DSC) test results indicated that the re-hydrogenated MgH2-Ni@NC composites consist of Mg2NiH4 and MgH2, with corresponding dehydrogenation activation energies of 75.2 and 82.9 kJ∙mol–1 respectively. The mechanism analysis revealed that Ni@NC was uniformly distributed on the MgH2 surface. During dehydrogenation/rehydrogenation, Mg2NiH4/Mg2Ni "hydrogen pumping" by Ni and MgH2/Mg occurred in situ, the presence of N-C effectively inhibited the expansion of MgH2/Mg, and the enhanced charge transfer effect was facilitated by N in the Ni@NC composite, synergistically enhancing the kinetic performance and cycling stability of MgH2.