The hydrogen storage properties and reaction mechanism of the MgH2-NaAlH4 composite system

Authors

M IsmailFollow
Yue Zhao, University of WollongongFollow
X B. Yu, University of Wollongong, NSW Australia
J F. Mao, University of Wollongong, NSW AustraliaFollow
S. X. Dou, University of WollongongFollow

RIS ID

42480

Publication Details

Ismail, M., Zhao, Y., Yu, X. B., Mao, J. F. and Dou, S. X. (2011). The hydrogen storage properties and reaction mechanism of the MgH₂-NaAlH₄ composite system. International Journal of Hydrogen Energy, 36 (15), 9045-9050.

Abstract

In this study, we report the hydrogen absorption/desorption properties and reaction mechanism of the MgH₂–NaAlH₄ (4:1) composite system. This composite system showed improved dehydrogenation performance compared with that of as-milled NaAlH₄ and MgH₂ alone. The dehydrogenation process in the MgH₂–NaAlH₄ composite can be divided into four stages: NaAlH₄ is first reacted with MgH₂ to form a perovskite-type hydride, NaMgH₃ and Al. In the second dehydrogenation stage, the Al phase reacts with MgH₂ to form Mg₁₇Al₁₂ phase accompanied with the self-decomposition of the excessive MgH₂. NaMgH₃ goes on to decompose to NaH during the third dehydrogenation stage, and the last stage is the decomposition of NaH. Kissinger analysis indicated that the apparent activation energy, E_A, for the MgH₂-relevent decomposition in MgH₂–NaAlH₄ composite was 148 kJ/mol, which is 20 kJ/mol less than for as-milled MgH₂ (168 kJ/mol). X-ray diffraction patterns indicate that the second, third, and fourth stages are fully reversible. It is believed that the formation of Al₁₂Mg₁₇ phase during the dehydrogenation process alters the reaction pathway of the MgH₂–NaAlH₄ (4:1) composite system and improves its thermodynamic properties.