Effect of Cr Doping on Microstructure and Hydrogen Storage Properties of Zr0.8Ti0.2CrxCo1−x (x = 0, 0.05, 0.1, 0.15) Alloys

The ZrCo hydrogen storage alloy is a relatively good hydrogen isotope carrier applied in the National Thermonuclear Fusion Reactor. However, the intrinsic disproportionation characteristics of ZrCo alloy reduces its cyclic service life and limits its further application. To address this issue, Zr0.8Ti0.2Co alloy is developed and exhibits good anti-disproportionation performance than pure ZrCo. Nevertheless, Zr0.8Ti0.2Co suffers from relatively poor hydrogen absorption kinetics. In this study, the effects of Cr substitution on its microstructure and hydrogen storage performance are investigated. Zr0.8Ti0.2CrxCo1−x (x = 0, 0.05, 0.1, 0.15) samples are composed of the ZrCo main phase. After Cr substitution, the second phases of CoZr2 and TiCr2 Laves phases appear. With the increase in Cr content, the lattice constant and unit cell volume of the Zr0.8Ti0.2Co alloy increase. Meanwhile, the hydrogen absorption incubation time of the Zr0.8Ti0.2Co alloy is shortened, and the activation performance is enhanced, which is attributed to the catalytic effect of the Laves second phases. The enthalpy of hydrogen absorption of the Zr0.8Ti0.2Co alloy increases, and the stability of the hydride is enhanced with increasing Cr addition. Zr0.8Ti0.2Cr0.05Co0.95 demonstrates excellent hydrogen desorption kinetics while maintaining robust anti-disproportionation performance. The element substitution and the composition design are effective approaches to improving the comprehensive hydrogen storage performance of ZrCo-based alloys, which provides guidance for its further application.