Abstract

Metal hydrides form large varieties of different types of materials. The traditional applications are related to hydrogen storage, but during the last decades it has found that these compounds are also important for batteries applications, smart windows, heat storage, magnetism and compressors.

During the last 15-20 years complex hydrides based on aluminum, boron and nitrogen, respectively, have been extensively investigated. Such materials have a much higher gravimetric hydrogen capacity than the traditional metal hydrides, and thus potential candidates for hydrogen storage applications. Recently it has been found that boron-based complex hydrides has a high Li conduction, and thus such materials are also possible candidates as solid state electrolytes in Li-ion batteries.

Hydrogen uptake and release are complicated in many of these compounds, with presence of several intermediate steps and phases that can be both crystalline and amorphous. Thus, synchrotron radiation X-ray diffraction in combination with neutron diffraction are the key methods for detailed structural characterization. Diffraction experiments during hydrogen desorption and absorption are important for clarifications of the intermediate phases and the processes for hydrogen uptake and release. Furthermore, catalysts and additives are important to promote the reactions, and therefore the combination of XANES/EXAFS and diffraction methods are needed to understand the effect of additives. Recent work with hydrides of high entropy alloys has shown the importance to use PDF-methods.

Selected examples of novel compounds, efforts to understand hydrogenation/dehydrogenation properties including effect of selected additives will be presented. The combination of neutron and synchrotron radiation X-ray scattering will in particular be emphasized.

The Research Council of Norway, EU FP7 and H2020 are acknowledged for financial support.

Fig. 1. Phase transformation in s-Mg(BH₄)₂ (Zavorotynska, Hauback et al., Energies (2015)).