Hydrogenation/ Dehydrogenation Kinetics Behaviors of MgH2 Powders Doped With 10wt % ZnO Nanoparticles

Introduction Hydrogen, which is enjoying a set of unique properties, offers the most potential solution to satisfying the global energy requirements for reducing carbon dioxide  leading to improve the global energy... [ view full abstract ]

Introduction

Hydrogen, which is enjoying a set of unique properties, offers the most potential solution to satisfying the global energy requirements for reducing carbon dioxide  leading to improve the global energy security. Recent studies have shown that hydrogen fuel cost is reasonable and can be considered as an ideal candidate to replace fossil fuels. Number of obstacles must overcome before the hydrogen economy becomes a reality. One of the obstacles is, safe and efficient storage of hydrogen particularly for mobile/automotive applications.

Method

Nano crystalline MgH₂ powders were prepared by reactive ball milling (RBM) technique under a hydrogen pressure of 50bar, using high-energy planetary ball mills. In these experiments, 5g of as -received Mg powders were charged into a stainless steel vial and together with 50 stainless steel balls in a glove box under argon-gas atmosphere. The vial was then removed out from the glove box and charged with 50- 70 bar H₂ gas. The RBM process was started under the initial hydrogen pressure, planetary-type ball mill operated at a rotational speed of 250rpm. The nanocatalytic effect of metals oxide powders prepared by sol gel technique on the hydrogenation properties and stability of MgH₂ powders were investigated. X-ray diffraction (XRD),high resolution transmission electron microscope (HRTEM), scanning electron microscope (SEM), differential scanning calorimeter (DSC) and Sieverts machine were utilized for characterization the physical and chemical properties of the synthesized samples. Long RBM time was investigated to decrease the grain sizes of MgH₂ and improve thekinetics of hydrogen absorption/desorption and destabilizing of µ-MgH₂phase. In addition, it led to decreasing the activation energy of the system.Nanocomposite MgH₂/10 wt. % TiO₂ powders showed pioneering hydrogenation properties, indexed by the high ability of absorbinghydrogen atoms  at very low pressure .

Conclusions

The catalytic effects of TM (ZnO) on the thermal stability represented (decomposition temperature) and hydrogenation properties,(absorption/desorption) of MgH₂ nanocrystalline powders, were investigated and found to be destabilizer additives of the MgH₂ phase.The particle size of the catalysts powders could play most vital role in improving the hydrogenation properties of MgH₂ and could lead to dramatic decrease on the decomposition temperature of the metal hydride phase.