Chapter 3.2 - Hydrogen storage in high entropy alloys

Abstract

Hydrogen has huge potential for utilization as an alternative fuel if it can be stored safely and efficiently. One option is to use the proper metals or alloys to store hydrogen as a solid hydride. Metal hydrides have been the subject of extensive research as potential storage materials but the majority of the alloys tested fall short of the standards for a competitive hydrogen storage unit that can be used in real-world scenarios. Five or more elements must be combined in equal or fairly substantial amounts to form high-entropy alloys (HEAs). A future hydrogen-based energy system will require enormous amounts of hydrogen storage, and the HEAs may provide a workable solution. This calls for the creation of alloys with a very high H/M ratio. If it is produced, hydrogen has great potential to be used as a substitute fuel. Greater ratios are possible in rare-earth alloys, where the H/M ratio for transition metal hydrides is typically not higher than 2. However, a H/M ratio of 2.5 can be attained in high entropy alloys by absorbing significantly more hydrogen than other competitive alloys. The high hydrogen-storage capability of the alloy is understood to be due to the lattice strain, which enables hydrogen to be absorbed in tetrahedral and octahedral interstitial sites. High entropy alloys, which may one day be used as hydrogen storage materials, will be covered in this book chapter in relation to their hydrogen storage capability.