Preparation and Characterization of Nanoscopic Solid State Hydrogen Storage Materials

Storing hydrogen in solid hydrides has the advantage of high hydrogen densities, which are needed for stationary and mobile applications. However, the properties of these materials must be further improved in order to meet the requirements. Nanostructuring has been proven to be a promising strategy to tailor the thermodynamics and kinetics of hydrides. Transmission electron microscopy (TEM) is an indispensable tool for the structural and chemical characterization of such nanosized materials, however, most hydrides degrade fast upon irradiation with the imaging electron beam due to radiolysis.
In the first part of this work, a methodology is developed to quantitatively investigate this phenomenon using valence electron energy loss spectroscopy on ball milled MgH2 as a model system. The dehydrogenation can be quantitatively explained by the inelastic scattering of the incident electrons by the MgH2 plasmon. A solution to this fundamental problem is theoretically studied by virtue of multislice TEM contrast simulations of a windowed environmental TEM experiment, which allows for the TEM analysis in hydrogen at ambient pressure.
In the second part, the nanoconfinement of the complex hydride LiBH4 is investigated. For this, a novel nanoporous aerogel-like carbon scaffold is used, which is synthesized by salt templating. It is shown that the hydrogen desorption temperature, which is above 400°C for bulk LiBH4, is reduced to 310°C upon this nanoconfinement with an onset temperature as low as 200°C. Partial rehydrogenation can already be achieved under moderate conditions (100 bar and 300°C). In contrast to recent reports on nanoconfined LiBH4, in-situ heating in the TEM indicates that both decomposition products (B and LiH) remain within the pores of the aerogel-like carbon.