Optimized Dehydrogenation of Magnesium Hydride with Fe and Cu Additives

Abstract

Solid state hydrogen storage with the use of MgH₂ has gained widespread attention because of its good reversible storage capacity. This metal hydride however slowly releases hydrogen at high temperatures ranging between 325 – 375 ^oC. An important feature required of MgH₂ is its ability to commence hydrogen release at a fast rate and reduced temperature. Transition metal-containing alloys/compounds having either Fe or Cu as the principal element have been used to improve the dissociation of hydrogen from MgH₂.  Studies involving the use of each metal in its elemental form as an additive are minimal. This study investigated the catalytic effects of elemental Fe and Cu on the hydrogen release performance of MgH₂ for potential applications in transportation and power generation. It was observed that MgH₂/Fe had a better dehydrogenation performance; the temperature of onset of MgH₂/Fe and MgH₂/Cu dehydrogenation were 205, and 215 ^oC which were 98 and 88 ^oC lower than that for as-received MgH₂.  The highest amount, 1.9 wt. % H₂ was released by MgH₂/Fe while 1.44 wt. % H₂ was released by MgH₂/Cu. The activation energy for dehydrogenation was reduced from 150.5 kJ/mol for as-received MgH₂ to 89.8 and 79.8 kJ/mol in MgH₂/Cu and MgH₂/Fe respectively. It took 18.8 min for as-received MgH₂ to commence dehydrogenation while that for MgH₂/Fe and MgH₂/Cu composites started from 12.2 and 13.4 min respectively. The in-situ formed Fe and Cu in MgH₂ after milling acted as active catalytic sites for its improved dehydrogenation with MgH₂/Fe behaving better.