Hydrogen storage mechanism of B- or Nb-doped Mg-Fe-based alloys: experimental and simulation

• Mg85Fe10Nb5(wt.%) alloy releases 3 wt% H 2 in 4 min at 633 K, 3 × faster than Mg85Fe10B5(wt.%) alloy. • Nb addition enables dual reversible reactions (Mg ↔ MgH 2 and Nb ↔ NbH), reducing dehydrogenation activation energy to 104.4 kJ/mol. • The “hydrogen pump” effect from NbH enhances nucleation and hydrogen diffusion, improving kinetics without altering thermodynamic stability (ΔH ≈ 74 kJ/mol). Magnesium-based hydrogen storage materials possess high theoretical hydrogen capacity but suffer from sluggish sorption kinetics. In this work, Mg85Fe10B5 and Mg85Fe10Nb5 (wt.%) alloys were prepared by vacuum induction melting, and their hydrogen storage behaviors were systematically investigated by kinetic measurements, pressure-composition-temperature analysis, and XRD, SEM, and TEM characterizations. First-principles calculations based on MgH 2 -B and MgH 2 -Nb models were further performed to clarify the local structural effects of B and Nb incorporation. At 633 K, Mg85Fe10Nb5 released 3 wt% H 2 within 4 min, whereas Mg85Fe10B5 required 12 min under the same conditions. The dehydrogenation activation energies were 104.4 and 147.4 kJ/mol, respectively. In contrast, the enthalpy changes for hydrogen absorption were 73.9 and 74.2 kJ/mol, indicating that B and Nb had little influence on thermodynamic stability. DFT results show that Nb induces stronger local lattice distortion and weakens neighboring Mg-H bonds more effectively than B. Therefore, both B and Nb improve hydrogen storage kinetics, while Nb exhibits a more pronounced promoting effect.