An overview of RE-Mg-based alloys for hydrogen storage: Structure, properties, progresses and perspectives

Rare earth (RE) elements have been successfully utilized in solid-state hydrogen storage as hydrogen-absorbing elements with excellent hydrogen storage properties in terms of safety and efficiency. RE-Mg-based hydrogen storage materials with high magnesium content are considered to be one of the most promising hydrogen storage materials for application due to their high mass/volume hydrogen storage density, moderate required hydrogen pressure, good reversibility, non-toxicity, and harmlessness. Furthermore, RE-Mg-based materials with low magnesium content and superlattice structure show great potential for application in the field of solid-state hydrogen storage. They are also widely used as anode materials for nickel-metal hydride batteries. In this paper, we comprehensively summarized and evaluated the organization and hydrogen storage properties of different RE-Mg system alloys (Mg-RE, Mg-RE-TM (TM=transition metals), and superlattice-type RE-Mg-TM) and the catalytic effect and mechanisms of catalysts on RE-Mg system alloys. The interactions between the types of RE elements, the contents of RE elements, the crystal structures, and the catalysts with the microstructure morphology and hydrogen storage properties of RE-Mg-based hydrogen storage alloys were established. The intrinsic mechanisms between microstructure morphology, phase structure, phase composition, and hydrogen storage properties of alloys with different RE-Mg-based systems were elucidated. By comparing the differences and characteristics between the organizational structures and hydrogen storage properties of different RE-Mg systems, a feasible idea and solution for the rational design and development of RE-Mg-based alloys with high hydrogen storage capacity, low cost, and fast hydrogen absorption and desorption kinetics was proposed.