期刊
PHYSICAL REVIEW B
卷 78, 期 22, 页码 -出版社
AMER PHYSICAL SOC
DOI: 10.1103/PhysRevB.78.224110
关键词
ab initio calculations; charge exchange; density functional theory; diffusion; hydrogen; interstitials; nanostructured materials; reaction rate constants; sodium compounds; surface energy; vacancies (crystal)
资金
- Delft Institute for Sustainable Energy (DISE)
- Delft University of Technology
- Stichting Nationale Computerfaciliteiten NCF/NWO
We report ab initio calculations based on density-functional theory, of the vacancy-mediated hydrogen migration energy in bulk NaH and near the NaH(001) surface. The estimated rate of the vacancy-mediated hydrogen transport, obtained within a hopping diffusion model, is consistent with the reaction rates of H-D exchange in nano-NaH at the relatively low temperatures observed in recent neutron studies on TiCl3-doped NaAlH4. We further obtained the formation energy for hydrogen vacancies and interstitials in NaH in all relevant charged states. These formation energies are too high to lead to the abundant hydrogen concentrations seen experimentally. Ab initio calculations on the NaCl//NaH interface are presented to provide an insight into the mechanism which may lead to high hydrogen concentrations. We show that the formation of an fcc-Na interlayer during the growth of NaH on top of NaCl is plausible, providing a source of vacancies and leading to fast hydrogen transport. The low interface energies for NaCl//NaH are consistent with an easy growth of NaH crystallites on NaCl nucleation centers, which may, therefore, act as grain refiners.
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