The applicants seek two days of beam time to study the magnesium hydroxide - lithium hydride hydrogen release system. This system can theoretically release 5.44% of hydrogen and has been investigated in our lab by TPD, PXD, SEM-EDX, TEM, IR and Raman spectroscopy. The reaction between nanostructured Mg(OH)2 and ball milled LiH leads to a halving in the desorption onset temperature with respect to the bulk materials and improved dehydrogenation kinetics. Based on our data, two multi-step mechanisms can be proposed. Our aim is to follow the reaction in-situ, with slow heating rates, using deuterated starting materials. The contrast in the neutron scattering lengths will allow us to identify all components during the steps of the reaction. Hence, PND data in combination with the results already obtained is crucial in order to fully understand the mechanism of hydrogen release.