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

✍ Scribed by M. Ismail; Y. Zhao; X.B. Yu; J.F. Mao; S.X. Dou

• Publisher: Elsevier Science
• Year: 2011
• Tongue: English
• Weight: 694 KB
• Volume: 36
• Category: Article
• ISSN: 0360-3199
• DOI: 10.1016/j.ijhydene.2011.04.132

✦ Synopsis

In this study, we report the hydrogen absorption/desorption properties and reaction mechanism of the MgH 2 eNaAlH 4 (4:1) composite system. This composite system showed improved dehydrogenation performance compared with that of as-milled NaAlH 4 and MgH 2 alone. The dehydrogenation process in the MgH 2 eNaAlH 4 composite can be divided into four stages: NaAlH 4 is first reacted with MgH 2 to form a perovskite-type hydride, NaMgH 3 and Al. In the second dehydrogenation stage, the Al phase reacts with MgH 2 to form Mg 17 Al 12 phase accompanied with the self-decomposition of the excessive MgH 2 . NaMgH 3 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 MgH 2 -relevent decomposition in MgH 2 eNaAlH 4 composite was 148 kJ/mol, which is 20 kJ/mol less than for as-milled MgH 2 (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 Al 12 Mg 17 phase during the dehydrogenation process alters the reaction pathway of the MgH 2 eNaAlH 4 (4:1) composite system and improves its thermodynamic properties.