In-operando stress measurement and neutron imaging of metal hydride composites for solid-state hydrogen storage

Solid-state hydrogen storage in metal hydrides offers highest volumetric energy storage densities and low working gas pressures at the same time. Recently developed metal hydride composites (MHC) consist of a hydride-forming metal alloy and a secondary phase, typically graphite, to realize form-stable composites and short loading and unloading times (< 5 min). Hydride formation causes a volume expansion of the storage material. Thus, it is mandatory to characterize this behavior for the sake of system safety. This work focuses on the in-operando characterization of the volume expansion of MHC that could trigger mechanical stresses acting on the walls and internal assemblies of the storage container. MHC with different metal particle shapes (flakes and powder) were studied. In-operando neutron imaging of axially freely expanding MHC was applied to analyze the time-resolved and spatial concentration of hydrogen, reaction fronts and the evolution of volume expansion and stability of the MHC. Stress measurements revealed that stresses of up to 330% of the respective operating gas pressure occur for confined MHC. Both techniques combined deliver crucial information and implications for the design of safe (according to ISO 16111), efficient and dynamic metal hydride storage systems.