Superior cycling stability of Zr-Hf-Co-Fe-Ni hydrogen isotope storage alloys achieved by hydrogen binding energy modulation

Abstract

Zr2Co alloy is a promising candidate for tritium capture in International Thermonuclear Experimental Reactor (ITER). However, its operational application is limited by the poor disproportionation resistance. In this work, Hf/Fe/Ni co-alloying was proposed to modulate the hydrogen storage properties of Zr2Co alloy, leading to the development of Zr1.5Hf0.5Co0.5FexNi0.5-x (x = 0.25, 0.3, 0.35, 0.4) alloys. The experimental results indicate that all as-cast alloys exhibit multi-phase structures. The main phase is tetragonal Zr2Co, accompanied by the cubic Zr2Co second phase. As Fe substitution in the alloys increases, the hydrogen storage capacity shows an increasing and then decreasing trend, and the hydrogenation equilibrium pressure gradually decreases. Among them, Zr1.5Hf0.5Co0.5Fe0.3Ni0.2 alloy exhibits the highest hydrogen storage capacity of 1.70 wt% with 1.61×10-6 Pa hydrogenation equilibrium pressure at room temperature. Notably, Zr1.5Hf0.5Co0.5Fe0.3Ni0.2 alloy also shows the best disproportionation resistance due to the minimum unit cell volume expansion after hydrogenation, low content of cubic Zr2Co phase, and the optimized distribution of hydrogen binding energy in interstitial sites. Its cyclic hydrogen storage capacity retention rate is 98.4% after 50 cycling tests. This work develops a high-performance tritium-getter material and provides a scientific basis for addressing tritium capture challenges.