Effects of Nd substitution and its content on hydrogen storage performance of TiFe-based alloys

Abstract

Alloying with transition metals or rare earth elements is a viable strategy to enhance the sluggish activation kinetics of TiFe-based alloys, which traditionally require severe temperature and pressure conditions for initial hydrogenation. This work investigates a series of alloys with the nominal composition Ti_1.1-xZr_0.1Nd_xFe_0.6Ni_0.3Mn_0.2 (x = 0-0.08), fabricated via vacuum induction melting with varying Nd concentrations. The as-cast microstructure reveals a characteristic multi-phase composition, consisting of a primary Ni-rich TiFe matrix, a secondary ZrMn₂ phase located at the matrix interfaces, and a separate Nd-rich phase. Incorporating Nd resulted in a notable refinement of the grain structure and an increased density of phase boundaries, which significantly reduced the incubation time required for activation. Gaseous hydrogen storage measurements indicated that the Nd-containing alloys exhibit excellent activation performance, achieving full activation in a single cycle at 373 K. The alloy with an Nd content of x = 0.04 achieved a maximum hydrogen absorption saturation rate of 96.9% at 363 K. Furthermore, the magnitudes of the enthalpy (ΔH) and entropy (ΔS) changes for the hydrogen sorption process showed a positive correlation with the Nd content.