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Understanding the Behaviour of Real Metaborates in Solution
Frances Pope1, Noë I Watson1, Antoine Deblais2
1Van't Hoff Institute for Molecular Sciences, University of Amsterdam, Science Park 904, 1098 XH, Amsterdam, The Netherlands.
Summary
Potassium borohydride solutions for hydrogen storage change dramatically with concentration. Concentrated solutions exhibit non-Newtonian behavior due to metaborate oligomers, impacting their practical application.
Area of Science:
- Materials Science
- Chemical Engineering
- Electrochemistry
Background:
- Alkali metal borohydrides are investigated for hydrogen storage.
- Potassium borohydride shows commercial potential due to spontaneous reaction with water, producing hydrogen gas.
Purpose of the Study:
- To investigate the physical and chemical properties of alkali metal borohydride self-hydrolysis solutions.
- To understand the impact of concentration on solution microstructure, rheology, and hydrogen evolution.
Main Methods:
- Monitoring hydrogen evolution and pH changes.
- Utilizing Nuclear Magnetic Resonance (NMR) spectroscopy to track reaction intermediates.
- Analyzing rheological properties of solutions at varying concentrations.
Main Results:
- Increasing borohydride concentration significantly alters microstructure and rheology, with critical changes above 10% w/w.
- Dilute solutions behave as Newtonian fluids, while concentrated solutions exhibit non-Newtonian behavior.
- Non-Newtonian behavior is attributed to the formation and entanglement of metaborate oligomers.
Conclusions:
- Concentration-dependent changes in rheology are crucial for practical hydrogen storage applications.
- Metaborate oligomer formation impacts the performance of borohydride-based hydrogen storage systems.
- Further research is needed to optimize borohydride solutions for efficient and safe hydrogen storage.
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