Achieving fast hydrogenation by hydrogen-induced phase separation in Mg-based amorphous alloys

Abstract

Mg-based amorphous alloys are one of the potential hydrogen storage materials. The challenges which are blocking application of such alloys involve unfavorable crystallization of amorphous phase in hydrogenation and dehydrogenation and sluggish low-temperature de/hydrogenation kinetics. To solve those challenges, the Mg60RExNi30−xCu10 (RE=La and Ce; x = 5, 7.5, 10 and 15) amorphous alloys were prepared by melt spinning and the structural transformation of amorphous phase and its correlation to hydrogenation kinetics has been investigated. It is observed that all the amorphous powders are able to absorb more than 3.0 wt%-H at 130 °C under 4.5 MPa-H2, and the hydrogen absorption rate of the Mg60RE10Ni20Cu10 amorphous alloys is much faster than other alloys by forming a dual amorphous phase structure during hydrogenation. XRD characterization of Mg60Ce10Ni20Cu10 hydrides proved that such dual amorphous phase structure is resulted by hydrogen-induced amorphous phase separation. According to EDX results, the dual amorphous phase structure consists of Ce-rich and Ni-Cu-rich domains with a size of about 5 nm which gradually form by element aggregation during hydrogen absorption. Meanwhile, it is also confirmed that the element aggregation is the precursor of hydrogen-induced crystallization as crystallization is observed in the Ni–Cu-rich domain. It is verified that the hydrogen-induced amorphous phase separation of the Mg-based amorphous alloys is tunable and can be used for obtaining superior hydrogenation performance. The hydrogen-induced structural evolution revealed in this work might inspire the development of new Mg-based hydrogen storage amorphous alloys.