Ammonia borane (AB) and sodium borohydride (SBH) are candidate materials for on-board hydrogen storage that can be dehydrogenated upon demand The rheological properties of the dehydrogenated by-products are important to quantify their removal and transportability from the hydrogen storage system This paper presents visco-elastic property (elastic stiffness and viscous damping) measurements of the spent fuels obtained from AB hydrolysis, hydrothermolysis and thermolysis, and SBH hydrolysis Smaller stiffness and larger mobility (or smaller viscous damping) indicate better transportability of the spent fuel In addition, flow property (dynamic angle of repose and avalanching time) measurements for the hydrolysis spent fuels of AB and SBH are also presented Comparing with the SBH hydrolysis spent fuel, the AB hydrolysis spent fuel had a lower stiffness and larger mobility, as well as lower angles of dynamic repose and avalanche power peaks, indicating that it is more transportable. Among all the investigated AB spent fuels in the present study, those obtained from its neat thermolysis (at 120 degrees C) and hydrothermolysis (40-70 wt%) were found to be the most transportable, followed by-products of its hydrolysis and ionic solvent-aided thermolysis, respectively (C) 2010 Professor T Nejat Veziroglu Published by Elsevier Ltd All rights reserved