Low melting point alkali metal borohydride mixtures for hydrogen storage

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Liu, Yinzhe (2018). Low melting point alkali metal borohydride mixtures for hydrogen storage. University of Birmingham. Ph.D.

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Abstract

With relatively high gravimetric and volumetric hydrogen capacities and low hydrogen operating pressures, borohydrides are being investigated for their potential use as solid-state hydrogen storage media. This work focuses on investigating the hydrogen sorption mechanisms for \(LiBH_4\)-based low-melting-point borohydride mixtures (e.g. \(0.62LiBH_4\)-\(0.38NaBH_4\), \(0.75LiBH_4\)-\(0.25KBH_4\)), and their destabilized systems using selected additives.

Solid solutions and bimetallic borohydride are found in the as-prepared \(0.62LiBH_4\)-\(0.38NaBH_4\) and \(0.75LiBH_4\)-\(0.25KBH\) mixtures, respectively. Under Ar, the \(0.62LiBH_4\)-\(0.38NaBH_4\) mixture releases 10.8 wt.% of hydrogen at 650 °C; whilst the \(0.75LiBH_4\)-\(0.25KBH_4\) mixture releases 8.9 wt.% of hydrogen at 700 °C. Their dehydrogenation peak temperatures are strongly affected by Na+ or K+ and therefore higher than \(LiBH_4\). These mixtures have poor cycling stabilities. Additives, such as micron-sized \(SiO_2\) and nano-sized Ni, cannot affect their melting points; but they cause lower dehydrogenation temperatures, decrease the hydrogen evolution, and facilitate the formation of metal dodecaborates. Besides, the addition of nano-sized Ni cannot significantly improve the cycling stability; however, it leads to partial reversible \(LiBH_4\).

Therefore, a further compositional optimization with respect to the rehydrogenation conditions, in parallel with the use of nano-confinement of the mixture via an infiltration approach, is needed before practical use of a low-melting-point alkali metal borohydride mixture.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

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