Synthesis, characterisation and decomposition properties of manganese-based borohydrides for hydrogen storage

Liu, Ruixia (2012). Synthesis, characterisation and decomposition properties of manganese-based borohydrides for hydrogen storage. University of Birmingham. Ph.D.

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Abstract

In this work, a series of Mn-based borohydrides were synthesized by mechanochemical milling of ABH\(_4\)-MnCl\(_2\) (where A=Li, Na, K) under argon. Samples prepared by milling xLiBH\(_4\)-MnCl\(_2\) (where x = 2 or 3) resulted in the formation of Mn(BH\(_4\))\(_2\) and LiCl in a stoichiometric ratio. Thermal decomposition of Mn(BH\(_4\))\(_2\) was observed between 105 and 180°C with the concurrent evolution of hydrogen and diborane. Analysis of the decomposition products suggested the presence of amorphous B, Mn and LiCl.
When NaBH\(_4\) was used as a reagent, Mn(BH\(_4\))\(_2\) was also observed, however instead of NaCl, a solid solution of NaCl\(_x\)(BH\(_4\))\(_1\)\(_-\)\(_x\) and Na\(_6\)MnCl\(_8\) were formed. Mn(BH\(_4\))\(_2\) decomposed between 110 and 170°C for xNaBH\(_4\)-MnCl\(_2\) with the concurrent evolution of hydrogen and diborane. Analysis of the decomposed samples showed that amorphous B and Mn formed (110 to 170°C) and NaCl\(_x\)(BH\(_4\))\(_1\)\(_-\)\(_x\) reacted with Na\(6\)MnCl\(_8\) to produce NaCl (250 to 475°C).
When KBH\(_4\) was used as a reagent, Mn(BH\(_4\))\(_2\) was not observed. Rather, K\(_2\)Mn(BH\(_4\))\(_4\), KMnCl\(_3\) and unreacted KBH\(_4\) were observed. The mass losses for the milled sample were observed between 100 to 160°C with a release of hydrogen and trace diborane, forming KBH\(_4\), B, and Mn, and between 165 to 260°C with only hydrogen release, giving KCl, B and Mn.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

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