Achieving excellent cycle stability in Zr–Nb–Co–Ni based hydrogen isotope storage alloys by controllable phase transformation reaction.

Hydrogen isotope (deuterium and tritium) as a special form of hydrogen energy, its storage in an efficient and safe way has been paid more and more attention by researchers in recent years. ZrCo alloy is regarding as the one and only promising material for large-scale storage of hydrogen isotope. However, poor cycle life and inferior capacity retention restrict its engineering application. Herein, we propose a co-substitution strategy of Nb (for Zr) and Ni (for Co) in ZrCo alloy to overcome the defects. Significantly, Zr 0.8 Nb 0.2 Co 0.8 Ni 0.2 alloy exhibits ultralong cycle life (97.6% retention) and remarkable capacity (2.42 H (f. u.)) in 100 cycles, which far exceeds all existing hydrogen isotope storage alloys (Pd, U and other ZrCo-based alloys). These outstanding performances are entirely revealed from two aspects: stable homogeneous structural phase transformation process of parent structure (Zr 0.8 Nb 0.2 Co 0.8 Ni 0.2 H 0.3 -B33 ↔ Zr 0.8 Nb 0.2 Co 0.8 Ni 0.2 H 2.8 -B33″) and ordered migration mechanism of H atom (layered and linear de-/intercalation). Our attractive insights into the ultralong cycle life of ZrCo-based alloys through homogeneous structural phase transformation will serve as a pioneer on cycle optimization in the field of hydrogen storage materials. [Display omitted] • The as-cast alloy containing B33 phase was successfully prepared according co-substitution strategy. • Zr0.8Nb0.2Co0.8Ni0.2 shows the highest cycle capacity and retention among all reported alloys. • The splendid cycle stability comes from B33↔B33'' homogeneous structural phase transformation. • A novel H migration mechanism is proposed to replenish the classical site occupation theory. [ABSTRACT FROM AUTHOR]