Recent advances in metastable alloys for hydrogen storage: a review

Development of new materials with high hydrogen storage capacity and reversible hydrogen sorption performances under mild conditions has very high value in both fundamental and application aspects. In the past years, some new systems with metastable structures, such as ultra-fine nanocrystalline alloys, amorphous alloys, nanoglass alloys, immiscible alloys, high-entropy alloys, have been abundantly studied as hydrogen storage materials. Many new hydrogen storage properties either from the kinetics or thermodynamics aspects have been reported. In this review, recent advances of studies on metastable alloys for hydrogen storage applications have been comprehensively reviewed. The materials preparation methods to synthesize metastable hydrogen storage alloys are firstly reviewed. Afterwards, hydrogen storage properties of the metastable alloys are summarized and discussed, focusing on the unique kinetics and thermodynamics properties by forming of such unique metastable structures. For examples, superior hydrogenation kinetics and higher hydrogen storage capacity have been achieved in Mg-based amorphous and nanoglass alloys. Destabilized thermodynamics properties can be obtained in the immiscible Mg-Mn and Mg-Zr alloys. In addition to highlighting the recent achievements of metastable alloys in the field of hydrogen storage, the remaining challenges and trends of the emerging research are also discussed.