Stability of Catalyzed Magnesium Hydride Nanocrystalline During Hydrogen Cycling. Part II: Microstructure Evolution

In Part I, the cyclic stabilities of the kinetics of catalyzed MgH₂ systems including MgH₂-TiH₂, MgH₂-TiMn₂, and MgH₂-VTiCr were investigated, showing stable kinetics at 300 °C but deteriorations of the hydrogenation kinetics at temperatures below 150 °C. The present Part II describes the characterization of uncycled and cycled catalyzed MgH₂ by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) analysis. XRD analysis shows the crystallite sizes of the Mg and MgH₂ significantly increased after the cycling. The mean crystallite sizes of the catalysts (TiH₂ and VTiCr) increased moderately after the cycling. SEM and TEM imaging were used to compare the microstructures of uncycled (as-milled) and cycled materials, revealing a drastic change of the microstructure after 100 cycles. In particular, results from energy-dispersive spectroscopy (EDS) mapping show that a change of distribution of the catalyst particles in the Mg and MgH₂ phase occurred during the cycling.