Ni-induced electronic modulation and structural resilience in TiMn-based AB₂-type alloys for ultra-stable hydrogen storage

TiMn-based AB₂-type alloys have emerged as promising candidates for large-scale hydrogen storage applications due to their high theoretical capacity, room-temperature reversibility, and cost-effectiveness. However, their practical deployment has been hindered by sluggish activation kinetics and insufficient cyclic stability. This study addresses these limitations through strategic Ni substitution at Fe sites in the B-side sublattice, guided by first-principles calculations and experimentally validated via vacuum arc melting. The optimized Ti_0.65Zr_0.35Cr_0.85Mn_0.95Fe_0.196Ni_0.004 alloy demonstrates exceptional hydrogen storage performance, attributed to the charge redistribution among all constituent atoms in the alloy, which is induced by the strong electronegativity of Ni. Crucially, this study demonstrates that optimizing hydrogen storage performance requires a dual consideration of electronic interactions and volumetric effects. The Ni-substituted alloy achieves unprecedented cyclic stability, retaining 1.91 wt.% capacity (100% retention) over 100 cycles at 318 K under 5.5 MPa H₂ pressure, and maintaining 99.46% capacity after 1000 cycles, which the highest reported durability for TiMn-based AB₂-type systems. Mechanistic analysis reveals that Ni substitution significantly enhances structural resilience by effectively suppressing lattice pulverization and mitigating cyclic stress-induced degradation, thereby maintaining a well-preserved micron-scale architecture throughout cycling. These findings provide transformative insights for designing high-capacity and long-lifespan AB₂-type alloys.