New-Generation Materials for Hydrogen Storage in Medium-Entropy Alloys.

This study presents the design, preparation, and characterization of thirty new medium-entropy alloys (MEAs) in three systems: Al-Ti-Nb-Zr, Al-Ti-Nb-V, and Al-Ti-Nb-Hf. The hardness of the alloys ranged from 320 to 800 HV 0.3 . Among the alloys studied, Al 15 Ti 40 Nb 30 Zr 15 exhibited the highest-reversible hydrogen storage capacity (1.03 wt.%), with an H/M value of 0.68, comparable to LaNi 5 , but with a reduced density (5.11 g·cm -3 ) and without rare earth elements. This study further reveals a strong correlation between hardness and hydrogen absorption/desorption; higher hardness is responsible for reduced hydrogen uptake. This finding highlights the interplay between a material's properties and hydrogen storage behavior in MEAs, and has implications for the development of efficient hydrogen storage materials.