A review of hydrogen storage and capacity decay in RE–Mg–Ni alloys: mechanisms and processes at the micro-scale

Abstract

Hydrogen storage capacity and cycle performance are critical factors for the effective hydrogen storage of RE–Mg–Ni based alloys. This paper summarizes the research progress aimed at enhancing the cycling properties of these alloys. Firstly, the hydrogen storage mechanism of various RE–Mg–Ni based alloys is summarized, including the lattice structure of the alloys and the hydrogen storage interstices occupied by hydrogen atoms in the hydrides. The factors contributing to the capacity decay of RE–Mg–Ni based alloys are also summarized, which include hydrogen-induced amorphous (HIA), phase decomposition, and lattice strain resulting from the hydrogen absorption and desorption reactions. Additionally, the reasons for the differences in lattice destruction among various alloys are discussed. The stable [A₂B₄] subunit/AB₂ alloy structure, improved superlattice subunits matching and improved cycle properties of various alloys are reviewed. Finally, the feasibility of combining stable [A₂B₄] subunit (by element occupancy) and lattice-stabilized multicomponent superlattice alloys is prospected.