Anisotropic storage medium development in a full-scale, sodium alanate-based, hydrogen storage system

•In-situ determination of alanate phase as a function of bed position and content.•Nondestructive analysis of a sodium alanate tank using neutron techniques.•Vehicle size tank tested with vehicle simulation tests prior to this analysis.•Identification of longitudinal concentration gradients.•Formation of paths for rapid hydrogen flow confirmed in-situ.

Deuterium desorption in an automotive-scale hydrogen storage tube was studied in-situ using neutron diffraction. Gradients in the concentration of the various alanate phases were observed along the length of the tube but no significant radial anisotropy was present. In addition, neutron radiography and computed tomography showed large scale cracks and density fluctuations, confirming the presence of these structures in an undisturbed storage system. These results demonstrate that large scale storage structures are not uniform even after many absorption/desorption cycles and that movement of gaseous hydrogen cannot be properly modeled by a simple porous bed model. Furthermore, the evidence indicates that there is slow transformation of species at one end of the tube indicating loss of catalyst functionality. These observations explain the unusually fast movement of hydrogen in a full scale system and shows that loss of capacity is not occurring uniformly in this type of hydrogen-storage system.