Electrochemical approaches to prepare magnesium-based hydrogen storage materials

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Copyright: Shen, Chaoqi
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Abstract
Magnesium hydride has been extensively investigated as a promising hydrogen storage candidate due to its high gravimetric capacity, but with high operational temperature and slow kinetics. However, a nanosizing approach and catalyst introduction may provide unprecedented opportunities to improve these properties. In this thesis, an electrochemical deposition method was developed to synthesise the magnesium-based nanostructures to enable hydrogen storage at low temperature. Firstly, the properties of components used in the electrochemical system such as magnesium precursors and stabilisers were investigated. It was found that functional groups in cationic, anionic and non-ionic stabilisers significantly influenced the morphologies of final magnesium deposits. The study was then extended to the hydrogen storage properties of Mg thin film formed on metal electrodes and results indicated that small magnesium particles (68 ± 11 nm) deposited on catalytic Ni substrate achieved low hydrogen desorption activation energy (37.8 ± 0.7 kJ·mol-1 H2). However, the heavy substrate limited the hydrogen capacity, thus the approach to generate isolated Mg nanoparticles was investigated with stabiliser and deposition current modifications. Mg nanoparticles prepared with a combination of cationic, anionic and non-ionic stabilisers could absorb 4 mass% H2 after hydrogenation at 100 °C. Since the electrochemical deposition method showed potential to prepare Mg nanoparticles with improvement of hydrogen storage properties, a catalyst (Ni) was introduced into the electrodeposition system via codeposition strategy. Mg/Ni nanocomposites were in-situ synthesised with different conditions, the final product with proper control was fully hydrogenated at 100 °C and exhibited a high content (30.6 %) of metastable γ-MgH2, which led to a low desorption temperature (< 200 °C). The external addition of catalysts was also studied but only showed minor improvements. Preliminary investigations of magnesium codeposited with carbon materials suspended in electrolyte did not exhibit better hydrogen storage properties compared to bulk magnesium, while a multilayered Mg/polypyrrole sandwich structure could absorb/desorb hydrogen at low temperature. Electrochemical deposition is still a novel method to synthesise magnesium-based hydrogen storage nanostructures, but it provides a highly promising avenue for practical developments in energy in the future.
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Author(s)
Shen, Chaoqi
Supervisor(s)
Aguey-Zinsou, Kondo-Francois
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Publication Year
2017
Resource Type
Thesis
Degree Type
PhD Doctorate
UNSW Faculty
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