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The effect of complex halides and binary halides on hydrogen release for the 2LiBH4:1MgH2 system
Zhuxian Yang1, David M Grant, Ping Wang
1Energy and Sustainability Research Division, Faculty ofEngineering, University of Nottingham, Nottingham, NG7 2RD, UK.
Faraday Discussions
|March 30, 2012
Summary
Doping lithium borohydride (LiBH4) with fluoride or chloride compounds, particularly LiBF4, significantly lowers its hydrogen release temperature. Combining LiBF4 with NbF5 further enhances hydrogen release from LiBH4 and MgH2 mixtures.
Area of Science:
- Materials Science
- Chemical Engineering
- Solid-state Chemistry
Background:
- Lithium borohydride (LiBH4) possesses high hydrogen storage capacity but suffers from high hydrogen release temperatures.
- Theoretical studies indicate that doping LiBH4 with halide anions (F-/Cl-) can lower the decomposition temperature.
- Investigating dopants and catalysts is crucial for improving the practical application of LiBH4 as a hydrogen storage material.
Purpose of the Study:
- To investigate the effect of halide-containing dopants on the hydrogen release properties of LiBH4.
- To evaluate the combined doping and catalytic effects of LiBF4 and NbF5 on the hydrogen release from a 2LiBH4:1MgH2 system.
- To assess the impact of rehydrogenation and cycling on the hydrogen release performance.
Main Methods:
- Synthesis and characterization of 2LiBH4:1MgH2 composites doped with various F-/Cl- containing compounds (LiBF4, NH4F, LiA1Cl4, NH4Cl).
- Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) to study hydrogen release profiles.
- Combined doping with LiBF4 and catalytic effect of NbF5 on hydrogen release.
- Partial rehydrogenation and cycling studies under elevated temperature and pressure.
Main Results:
- LiBF4 was identified as the most effective dopant among the studied halide compounds for improving hydrogen release from 2LiBH4:1MgH2.
- The combined use of LiBF4 and NbF5 significantly reduced the hydrogen release temperatures by 55°C for LiBH4 and 112°C for MgH2.
- After partial rehydrogenation and cycling, the LiBH4 component showed a further decrease in hydrogen release temperature, while the MgH2 component's temperature increased.
Conclusions:
- Halide doping, especially with LiBF4, is an effective strategy to lower the hydrogen release temperature of LiBH4-based materials.
- The synergistic effect of LiBF4 doping and NbF5 catalysis substantially enhances the hydrogen storage performance of the 2LiBH4:1MgH2 system.
- Cycling stability needs further optimization, as the MgH2 component's hydrogen release temperature increased after rehydrogenation.
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