Destabilisation of magnesium hydride by germanium as a new potential multicomponent hydrogen storage system

Abstract

MgH(2) has too high an operating temperature for many hydrogen storage applications. However, MgH(2) ball-milled with Ge leads to a thermodynamic destabilisation of >50 kJ mol(-1)(H(2)). This has dramatically reduced the temperature of dehydrogenation to 130 °C, opening up the potential for Mg-based multicomponent systems as hydrogen stores for a range of applications.

Mg-based compounds for hydrogen and energy storage

“…High-pressure DSC results gave a dehydrogenation endothermic peak at 235°C (regardless of the hydrogen back pressure used, from 0 to 25 bar) [20]. Modifying the sample with a Ti-based additive reduced the dehydrogenation even further, starting at 130°C (also confirmed in Fig.…”

“…3) [16]. The enthalpy of formation for Mg 2 Ge is 104.6 kJ/mol, which gives an enthalpy of dehydrogenation for 2MgH 2 :Ge of 23.0 kJ/mol, yielding a T(1 bar) of -91.6°C [20]. Interest in the use of Ge was initially as an additive for improving the kinetics of MgH 2 [21].…”

“…Ball-milling the elements Mg and Ge together led to the formation of Mg 2 Ge dispersed in a Mg matrix. Unfortunately, the Mg 2 Ge was not found to have any positive effect on the hydrogenation of the remaining Mg. Ball-milling MgH 2 with Ge was found to be an effective way to limit the formation of Mg 2 Ge phase, but still produces an intimate mixture of the two starting phases [20]. It has also been found that ball-milling MgH 2 and Ge under a hydrogen atmosphere reduces the amount of Mg 2 Ge formed even further, presumably through suppressing the formation of Mg metal during milling, which reacts more readily with the Ge [22].…”

MgH2 Dehydrogenation Thermodynamics: Nanostructuring and Transition Metal Doping

“…10 Nanostructuring and doping are popular methods of modifying properties of materials, as is the case for MgH 2 . Nanostructuring, via ball-milling, 11,12 or via wet-chemical synthesis using surface monolayer protection, 13,14,15 has being perceived to reduce the enthalpy for dehydrogenation. If H 2 release is a surface-desorption limited process, 16 then nanostructuring may modify surface curvature, hence dehydrogenation thermodynamics, and increase the specific surface area, hence dehydrogenation kinetics.…”

Catalytic Application of Carbon‐based Nanostructured Materials on Hydrogen Sorption Behavior of Light Metal Hydrides

“…After decades of extensive studies, it has been found that among different complex hydrides, NaAlH 4 and Li-Mg-N-H systems show promising storage behavior. The MgH 2 is also known as a potential hydrogen storage material because of its high gravimetric hydrogen storage capacity (7.6 wt% and 0.11kg/L) [13,14], high abundance (abundance in both earth crust and in sea water), acceptable cost, nontoxicity and high safety [13][14][15][16][17]. The sluggish sorption kinetics and high desorption temperature are the major limitations for these promising materials.…”