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

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/Zr2FeHx + 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.