The hydrogen storage properties of MgH2–Fe7S8 composites

Abstract

Nanostructured Fe₇S₈ was successfully synthesized and its catalytic effect on hydrogen absorption/desorption performance of MgH₂ is systemically discussed. The MgH₂ + 16.7 wt% Fe₇S₈ composite prepared by ball-milling method offers a striking catalytic activity for hydrogenation kinetics, and also reduces the initial decomposition temperature for MgH₂. The composite of MgH₂–Fe₇S₈ can absorb 4.000 wt% of hydrogen within 1800 s at 473 K, which is about twice that of pristine MgH₂ (1.847 wt%) under the same conditions. The onset hydrogen release temperature of Fe₇S₈-modified MgH₂ is 420 K, which is 290 K lower than that of additive-free MgH₂ (710 K). Meanwhile, the doped sample could release 4.403 wt% of hydrogen within 1800 s at 623 K as compared to 2.479 wt% of hydrogen by MgH₂. The activation energy for MgH₂–Fe₇S₈ is about 130.0 kJ mol⁻¹, approximately 36 kJ mol⁻¹ lower than that of MgH₂. The hydriding process of MgH₂ + 16.7 wt% Fe₇S₈ follows the nucleation and growth mechanism. The prominent hydrogen storage performances are related to the reactions between MgH₂ and Fe₇S₈. The newly formed MgS and Fe in the ball-milling process present a co-catalytic effect on the hydrogen storage performance of MgH₂.