Mechanism of hydrogen residue in metal hydrides formed from high-entropy alloys by inelastic neutron spectroscopy

High-entropy alloys (HEAs) typically contain four or more principle elements in equimolar amounts. We have recently discovered the first bcc HEA-based hydride with reversible hydrogen storage capacity at room-temperature, TiVCrNbH8. In addition, this material excels at many of the traditional showstoppers for applied hydrogen storage in intermetallic hydrides, i.e. degradation after repeated hydrogen absorption/desorption cycling, surface passivation and slow hydrogen sorption kinetics. This material is therefore promising as a future hydrogen storage material. However, the reversible capacity is 1.96 wt.% H2 while the full capacity in TiVCrNbH8 is 3.14 wt.% H2. This means that there are certain interstitial sites within the metal matrix where the H-atoms are bound more tightly than others. If these sites can be destabilized, the full hydrogen storage capacity of would become accessible.