Improved hydrogen cycling kinetics of nano-structured magnesium/transition metal multilayer thin films

A magnesium-based nano-structured multilayer material was developed by magnetron-assisted physical vapour deposition with promising hydrogen storage properties. The material has a reversible capacity of 4.6 wt% at temperatures between 250 and 350 °C and hydrogenates in <10 min at 250 °C. An activation energy of the dehydrogenation reaction of Ea = 71.6 kJ mol−1 was measured by differential scanning calorimetry. Structural analysis by TEM and SEM showed that the thin magnesium layers of 16.5 nm thickness interspersed with 2.5 nm of an amorphous, nickel-rich transition metal mix resulted in a favourable nanostructure after hydrogen cycling at up to 350 °C. The material also retained its fast kinetics and capacity for the 50 cycles that the material underwent. Comparison of XRD data with TEM shows that the layer thickness of such nano-structured, directional Mg layers in PVD multilayers can be reliably estimated by XRD. In addition the XRD texture relates to the microstructural evolution of the multilayered structure pre- and post-cycling.