Abstract
A series of CeH2.73/CeO2 composites with different ratios of hydride and oxide phases are prepared from the pure cerium hydride via oxidation treatments in the air at room temperature, and they are subsequently doped into Mg2NiH4 by ball milling. The desorption properties of the as-prepared Mg2NiH4+CeH2.73/CeO2 composites are studied by thermogravimetry and differential scanning calorimetery. Microstructures are studied by scanning electron microscopy and transmission electron microscopy, and the phase transitions during dehydrogenation are analyzed through in situ X-ray diffraction. Results show that the initial dehydrogenation temperature and activation energy of Mg2NiH4 are maximally reduced by doping the CeH2.73/CeO2 composite with the same molar ratio of cerium hydride and oxide. In this case, the CeH2.73/CeO2 composite has the largest density of interface among them, and the hydrogen release effect at the interface between cerium hydride and oxide plays an efficient catalytic role in enhancing the hydrogen desorption properties of Mg2NiH4.
Highlights
With the advantages of abundant natural resources and no pollution to the environment, hydrogen has been widely considered as an ideal carbon-free energy carrier
In order to clarify the effect of cerium hydride/oxide composites on the dehydrogenation properties of Mg2NiH4, in the present study, a series of CeH2.73/CeO2 composites with different ratios of cerium oxide and hydride were synthesized from pure cerium hydride via controlled oxidation treatments in the air at room temperature, and they were doped into Mg2NiH4 by ball milling
These results wellaccord with our previous finding on the effect of CeH2.73/CeO2 composites on the dehydrogenation properties of MgH2 (Lin et al, 2014), which means the CeH2.73/CeO2 composite with the same molar ratio of cerium hydride and oxide could be a good catalyst for the dehydrogenation properties of Mg-based hydrogen storage materials, including both MgH2 and Mg2NiH4
Summary
With the advantages of abundant natural resources and no pollution to the environment, hydrogen has been widely considered as an ideal carbon-free energy carrier. Doping catalysts by ball milling is a commonly-used and efficient method to enhance the hydrogenation/dehydrogenation kinetics of Mg-based materials (Ouyang et al, 2014a,b; Wang and Wang, 2017). We previously reported that CeF4 was an efficient catalyst to enhance the hydrogen storage properties of MgH2 (Lin et al, 2015), which can lead to reduced dehydrogenation temperature and activation energy because of the formation of new Mg-Ce-F species on the surface of MgH2. In order to clarify the effect of cerium hydride/oxide composites on the dehydrogenation properties of Mg2NiH4, in the present study, a series of CeH2.73/CeO2 composites with different ratios of cerium oxide and hydride were synthesized from pure cerium hydride via controlled oxidation treatments in the air at room temperature, and they were doped into Mg2NiH4 by ball milling. The microstructures of the Mg2NiH4-Ce2.73/CeO2 composites were observed by backscattered electron imaging using scanning electron microscope (SEM) and transition electronic microscopy (TEM)
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