Hydrogen storage alloys are considered to be a kind of good hydrogen storage medium, and their high hydrogen absorption and desorption capacity during cycling is the focus of research. However, their capacity degradation is unavoidable. The main degradation mechanisms are alloy particle pulverization, electrochemical corrosion and oxidation, and hydrogen-induced amorphization (HIA), in which HIA occurs in the AB2 type alloy hydride containing Laves phase or AB3-3.8 type rare earth nickel alloy hydrides containing Lave phase subunits. The factors affecting the occurrence of HIA are mainly hydrogen concentration, hydrogen pressure, temperature, number of cycles, and phase type. When the hydrogen concentration is low,HIA occurs in a part of alloy hydride after hydrogen absorption. The degree of HIA increases with the increase of hydrogen concentration. Whether the HIA occurs is completely related to the critical value of hydrogen pressure and temperature. When the value is over the critical value, HIA phenomenon is getting severe, when the value is lower than the critical value, the crystals coexist with the crystalline hydride. As the increase of cycling number, the HIA phenomenon is getting severe, which directly reduces the hydrogen desorption efficiency of the alloy. Phase tuning has been proved that can improve the hydrogen absorption and desorption properties of the alloy. Mg, Pr, Sm and Co, Mn, Cu, Fe and Al are applied to partly replace RE and Ni in the RENi2 (RE=rare earth) alloy, respectively. HIA inevitably occurs when the formed alloys absorb hydrogen, nevertheless, their hydrogen absorption and desorption properties of the alloy have been improved. The analyzed results show that after partial substitution of elements, the alloy phase transforms from a single AB2 type structure to the coexistence phases of AB2 type Laves phase and CaCu5 type AB5 phase. HIA occurs after hydrogen absorptionin AB2 phase, while AB5 phase is always crystalline. With the increase of cycling numbers, the HIA rate of the alloy is different when Ni is partly replaced by Fe, Mn and Si. For the phases containing AB2 unit or AB2 subunit, the sequence of HIA occurrence from easy to difficult is (La, Mg)Ni2> (La, Mg)Ni3> (La, Mg)2Ni7> (La, Mg)5Ni19. In order to delay or inhibit HIA, appropriate replacement of alloy elements, increasing the proportion or content of AB5 structural layer and recrystallization of alloy hydride may be investigated. In this paper, the research progress of HIA during hydrogen absorption is summarized in the alloy containing AB2 unit or AB2 subunit. The necessary conditions, influencing factors, phenomena and causes for HIA occurrence are introduced respectively. The delay measures of HIA are put forward and their prospects are forecasted, aiming to provide references for the development of hydrogen storage alloys with long life and high capacity. © 2020, Materials Review Magazine. All right reserved.
