Hydrogen storage is one of the great challenges limiting the commercialization of hydrogen (H2) PEM fuel cell technology for automobile and unmanned vehicles. Magnesium borohydride is one of the few materials that has a demonstrated gravimetric hydrogen storage capacity great than 11 wt% and thus a demonstrated potential to be utilized in a hydrogen storage system meeting practical vehicular hydrogen storage targets. Magnesium borohydride is abundant and cost competitive, it has one of the highest hydrogen capacity (14.9 wt % H2) and lowest enthalpy (~50 kJ/mol) of dehydrogenation. However, due to very slow kinetics, cycling between Mg(BH4)2 and MgB2 has been accomplished only at high temperature (~400 oC) and under high charging pressure (~900 bar). In this talk an innovative approach to vastly improve the kinetics of hydrogenation of bulk MgB2 to Mg(BH4)2 using additives such as ethers will be discussed. Our results demonstrate for the first time hydrogenation of bulk MgB2 to Mg(BH4)2 at temperatures as low as 300 oC. For instance, significant mass loss of about 5 wt% is observed for MgB2 samples pretreated with tetrahydrofuran followed by hydrogenation at 300 oC and 1000 bar, Figure 1. The selected additives effectively destabilize MgB2 allowing, for the first time, the simultaneous lowering of the MgB2/Mg(BH4)2 system hydrogenation temperature and hydrogenation pressure to 300 oC and 700 bars, respectively. The Mg(BH4)2 formation was confirmed by 11B NMR, XRD and TGA-DSC analyses. The effect of the selected additives on the bulk MgB2 hydrogenation process will also be discussed. Our approach has potential to significantly increase the cycling kinetics of the MgB2/Mg(BH4)2 system to lightweight fuel cell vehicle relevant conditions, whilst maintaining the other practical performance targets.

Activated magnesium boride based materials for hydrogen storage

255th National Meeting (2018)

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