A potential hydrogen isotope storage material Zr₂Fe: deep exploration on phase transition behaviors and disproportionation mechanism

Abstract

Tritium, a radioactive isotope of hydrogen, is exceptionally rare and valuable. The safe storage, controlled release and efficient capture of tritium are subject to focused research in the International Thermonuclear Experimental Reactor. However, the application of an efficient tritium-getter material remains a critical challenge. Zr₂Fe alloys exhibit a strong ability to absorb low-concentration hydrogen isotopes, but their practicability suffers from disproportionation reaction. Yet, the essential de-/hydrogenation performances and disproportionation mechanism of Zr₂Fe are inconclusive. Here, we designed a comprehensive series of measurements that demonstrate the ultra-low hydrogenation equilibrium pressure (2.68 × 10^-8 Pa at 25 °C) and unique hydrogen-interacted phase transitions in Zr₂Fe-H systems. Further kinetic and thermodynamic analyses reveal the causative reasons for disproportionation and determine the triggering temperature of the disproportionation reaction to be 375 °C in static hydrogen environments. Utilizing inversion of the Van't Hoff equation, higher-temperature hydrogen absorption models of Zr₂Fe are developed, supporting a solution to the inaccuracy and inseparability of the general de-/hydrogenation and disproportionation, thereby verifying the unique disproportionation route (Zr₂Fe/Zr₂FeH_x + H₂ → ZrFe₂ + ZrH₂). Combined with the density functional theory (DFT) calculations, the de-/hydrogenation and disproportionation mechanisms and their interrelation can be explained in depth. This work supports the exploration and modification of the Zr₂Fe-H and other metal hydride storage systems in future studies.

Keywords

Tritium-getter materials / Zr₂Fe alloy / phase transition / disproportionation mechanism / DFT calculations

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