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Exploration of Metal Hydride Systems with High Adsorption/Desorption Pressure

Subject Area Solid State and Surface Chemistry, Material Synthesis
Physical Chemistry of Solids and Surfaces, Material Characterisation
Term from 2020 to 2024
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 449160425
 
Final Report Year 2025

Final Report Abstract

In the past, the focus in the development and investigation of potential hydrogen materials, in particular metal hydrides, was on materials based on light metals and for application at comparatively low hydrogen pressures (< 200 bar). More recently, however, interest has developed in metal hydrides for high-pressure applications, i.e. for pressures > 200 bar, on the one hand to reduce the necessary binding enthalpies for material hydrogen storage and on the other hand to develop materials for heat-driven hydrogen compressors. The aim of the project was therefore to create the experimental basis to routinely measure hydrogen storage capacities by volumetric measurement at high pressures and to synthesize and characterize metal hydride systems whose hydrogenation properties have not been in focus so far, as they were either considered too unstable, i.e. with too high equilibrium pressure, or of too low capacity. In the project, two Sieverts devices were developed that are suitable for volumetric measurement of hydrogen uptake at limit pressures of approx. 400 bar and 1000 bar, respectively. The material investigations of both groups focused on the one hand on complex metal hydrides and so-called HEAs (high entropy alloys). The Freiberg group's investigations focused on complex hydrides (boranates and alanates) with cations of the second main group as well as transition and rare earth metals (Mg(AlH4)2, Ca(AlH4)2, Sr(AlH4)2, CaAlH5 , CeAlH6, Ca(BH4)2, Sr(BH4)2, Ba(BH4)2, Zr(BH4)4, Hf(BH4)4, Y(BH4)3). The Mühlheim group focused on Yb(AlH4)3 and on HEAs (high entropy alloys) based on Ti, Zr, Al combined with two other elements (Cr, Mn, Fe). In both groups, the materials were mostly produced by mechanochemical means (ball milling), whereby a special feature was that this was carried out in part and for the first time under a hydrogen atmosphere with a clear effect on the success of the synthesis. Closer examination of the processes involved in the mechanochemical synthesis of complex metal hydrides based on the combination of metal halides Li and sodium alanate showed that the general assumption that the by-products can be regarded as inert does not apply, but that they may well have the system controlling properties. The results and the material data obtained were published in a total of eight peer-reviewed articles.

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