Formation of hydride phase and diffusion of hydrogen in the V-H system varied by substitutional Fe

We elucidate the effect of Fe addition on the phase transformation and the diffusion of hydrogen in the V-H system. V forms monohydride (β) and dihydride (γ) phases by hydrogenation. The γ phase of VH2 has a face centered cubic (FCC) structure but V1−xFex (0.03 ≤ x ≤ 0.10) forms the FCC hydride phase though the hydrogen content is less than half of VH2, resulting in decreasing the hydrogen storage capacity. On the other hand, for the β phase proton nuclear magnetic resonance (1H NMR) demonstrates that addition of Fe increases the density of states at the Fermi energy N(EF) and the activation energy for hydrogen diffusion EH. This indicates that Fe has the effects of stabilizing the hydride phase and of suppressing the diffusion of hydrogen in the V-H system.