Effect of isostructural phase transition on cycling stability of ZrCo-based alloys for hydrogen isotopes storage

Abstract

ZrCo alloy as a promising candidate for hydrogen isotopes storage and delivery in the international thermonuclear experimental reactor (ITER) has attracted considerable attention. However, its capacity retention after 50 cycles is 22.4%, resulting from the disproportionation reaction during repeated phase transitions between cubic ZrCo phase and orthorhombic ZrCoH3 phase. Herein, a single isostructural phase transition with high thermal stability and structural stability in ZrCo-H system is achieved by multicomponent substitution for the first time. Considering the computational screening results, cost and gravimetric hydrogen capacity, a series of Zr0.8Nb0.2Co0.6Cu0.4−xNix (x = 0.2–0.3) alloys are designed and synthesized. The compositional dependence of phase component is further discussed in detail. Specifically, Zr0.8Nb0.2Co0.6Cu0.15Ni0.25 alloy with single orthorhombic phase exhibits high thermal stability (up to 550 °C) and maintains the orthorhombic structure during the de-/hydrogenation process at 380 °C. Thermodynamic destabilization of hydride (ΔH = 71.95 kJ·mol−1 H2) and nearly no de-/hydrogenation hysteresis contribute to a significantly low desorption temperature of 283 °C at 100 kPa. Thanks to superior thermal stability and structural stability, no attenuation of hydrogen storage performances including thermodynamics and kinetics can be observed during 200 de-/hydrogenation cycles, and the supereminent cycling stability of 100% and cyclic hydrogen capacity of 1.65 wt% are achieved. Combined with first-principles calculations, the improved cycling stability of Zr0.8Nb0.2Co0.6Cu0.15Ni0.25 alloy can be ascribed to the reduced lattice expansion and atomic motion during the orthorhombic isostructural phase transition.