Phase structure evolution and performance divergence in AB₂-type alloys induced by Al and Fe elemental substitution

Abstract

This work investigated the crystal structure, hydrogen storage, and electrochemical properties of the Ti_0.2Zr_0.8(V_0.2Mn_0.8)_1−xM_xNi_1.0 (M = Al, Fe; x = 0, 0.05, 0.1) Zr-rich AB₂ alloys. Rietveld refinement of X-ray diffraction (XRD) revealed that C14 phase abundance increased with Al content, while Fe promoted C15 phase formation, accompanied by a variation in the lattice constants. Hydrogen storage experiments showed C15 phase abundance positively correlated with maximum adsorption capacity, while plateau pressures were negatively correlated with lattice constants. The Fe_0.1 alloy exhibited the largest adsorption capacity and the highest plateau pressure, whereas the Al_0.1 alloy displayed opposite characteristics. All alloys demonstrated rapid hydrogen adsorption kinetics, reaching 98% capacity within 1 min after 5 activation cycles, retaining no obvious capacity decay after 20 cycles. Electrochemical studies indicated that Fe doping enhanced discharge capacity and high-rate discharge (HRD) performance due to increased C15 phase abundance. Electrochemical kinetics revealed that the improved HRD performance can be attributed to the enhanced electrocatalytic performance and hydrogen diffusion rate in Fe-doped alloys. This work provides a systematic analysis of how Al and Fe doping influences the AB₂-type Laves phase alloys, offering theoretical and experimental evidence for alloy design and optimization.

Keywords

AB₂ alloy / Laves phase alloy / hydrogen storage properties / nickel–metal hydride battery / electrochemical performance

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