Hydrogen storage is considered to be one of the principal technological barriers in the transition towards a hydrogen-based economy. In this proposal, we plan to look at the key materials that Toyota is using in their hydrogen car demonstrators. Toyota have found that vanadium-based alloys are highly promising because of their high volumetric hydrogen densities and moderate hydrogen absorption and desorption temperatures. However, structural reasons for reduced cycle performance have still to be understood. We ask for 2 days of beam-time on the high-flux GEM diffractometer to perform a detailed study ofthe hydrogenation/dehydrogenation of the two compositions Ti25Cr50V20Mo5 and Ti10Cr10V75Mo5 that involves the analysis of average structure and microstructure by the Rietveld method and also the local structure by PDF analysis.