Superior hydrogen storage in high entropy alloys

TLDR

Metal hydrides are promising for hydrogen storage, but achieving a very high hydrogen‑to‑metal ratio (H/M) is challenging, as typical transition metal hydrides max out at H/M = 2 and higher ratios are usually limited to rare‑earth alloys. The study aims to demonstrate that a high‑entropy alloy TiVZrNbHf can absorb more hydrogen than its individual constituents, reaching an H/M ratio of 2.5. The authors attribute the alloy’s superior storage capacity to lattice strain that facilitates hydrogen absorption in both tetrahedral and octahedral interstitial sites. The results confirm the alloy’s enhanced hydrogen uptake and suggest that high‑entropy alloys hold promise as future hydrogen storage materials.

Abstract

Abstract Metal hydrides (MH x ) provide a promising solution for the requirement to store large amounts of hydrogen in a future hydrogen-based energy system. This requires the design of alloys which allow for a very high H/M ratio. Transition metal hydrides typically have a maximum H/M ratio of 2 and higher ratios can only be obtained in alloys based on rare-earth elements. In this study we demonstrate, for the first time to the best of our knowledge, that a high entropy alloy of TiVZrNbHf can absorb much higher amounts of hydrogen than its constituents and reach an H/M ratio of 2.5. We propose that the large hydrogen-storage capacity is due to the lattice strain in the alloy that makes it favourable to absorb hydrogen in both tetrahedral and octahedral interstitial sites. This observation suggests that high entropy alloys have future potential for use as hydrogen storage materials.