Structural evolution of a Mg–C composite over 1000 H2 storage cycles

A material of magnesium containing 5 wt % carbon is brought to 1000 hydrogen sorption cycles with systematic sampling for material characterization. The Mg–5C material is cycled isothermally at 330 °C using an in-house hydriding rig. Samples removed from the reactor are analyzed using powder X-ray diffraction (XRD) and scanning electron microscopy (SEM) with additional transmission electron microscopy (TEM) on a subset of samples. These data are compared to cycling performance with the aim of finding correlations between material performance and structural evolution. The microstructure is shown to evolve in two stages. The first is the rapid transformation of the as-milled material into a high-aspect ratio structure. The second stage is the slow agglomeration and densification of the evolved structure via sintering. After 1000 cycles, the material retains nearly 88% of its peak hydrogen capacity.