Recent advances in substitutional doping of AB5 and AB2 type hydrogen storage metal alloys for Ni-MH battery applications

Abstract

Hydrogen absorption and desorption in metal alloys are of great interest for application as negative electrode materials in environment-friendly nickel-metal hydride (Ni-MH) aqueous batteries as well as safe hydrogen storage applications. In this review, we bring forward the recent development and new insights on the substitutional doping of the two key MH alloys, AB₅-type rare-earth alloy, and AB₂-type Laves phase alloys for application in Ni-MH batteries. The substitutional doping in the A or B sites of the AB₅-type and AB₂-type alloys is significant in enhancing performance and stability for hydrogen storage and as an anode material of Ni-MH batteries. The rare-earth site A and transition metal site B in an AB₅-type alloy have been doped by several other rare-earth and transition metal elements with various compositions. Similarly, A and B sites containing transition metals of the AB₂-type Laves phase alloys are doped with other rare-earth and transition metals in different compositions to develop novel MH alloys. Further, high entropy alloys (HEAs) are studied to obtain better chemical activity and stability for hydrogen storage at room temperature as a prospective material for application in Ni-MH batteries. Thus, this review provides a detailed understanding on the doping approaches for the two key MH alloys of AB₅-type and AB₂-type alloys, additionally, HEAs as novel electrode materials for Ni-MH batteries and hydrogen storage energy technologies.