Experimental and Theoretical Investigation on the Enhanced Hydrogen Storage Performance of Ti–Cr–Mn–Fe-Based Alloys Modified by Nb Substitution

Ti 1.02 Nb x Cr 1.0– x Mn 0.6 Fe 0.4 ( x = 0, 0.01, 0.02, and 0.05) and Ti 1.02– y Nb y Cr 1.0 Mn 0.6 Fe 0.4 ( y = 0, 0.02, 0.05, and 0.08) alloys were prepared through induction levitation melting, and their crystal structure characteristics and hydrogen storage properties were investigated by experiments and first-principles calculations. The alloys exhibit a main C14-Laves phase with fine element homogeneity and minor oxides. As the Nb stoichiometry in Ti 1.02 Nb x Cr 1.0– x Mn 0.6 Fe 0.4 ( x = 0–0.05) alloys increases, the alloy exhibits enhanced hydrogen absorption/desorption kinetics and capacity, despite an increased plateau slope due to improved hydrogen affinity. The Ti 1.02– y Nb y Cr 1.0 Mn 0.6 Fe 0.4 ( y = 0–0.08) alloys show simultaneous hysteresis amelioration and plateau pressure increment as the Nb content increases, thanks to hydride destabilization and expanded interstitials. The effects can be attributed to the medium atomic size and hydrogen affinity of Nb. Moreover, the first-principles calculation results indicate preferential occupancy at 4f sites of Nb in Ti–Cr–Mn–Fe-based alloys, and an expanded crystal lattice can be achieved with Nb substitution for Cr or Ti. This work shows that Nb substitution can be a promising strategy for the hydrogen storage performance enhancement of Ti–Cr-based Laves phase alloys for hydrogen compression applications.