Events

Hydrogen has become an important vector of energy as the world continues to transition to renewable energy. The way how hydrogen is stored has strongly evolved from using gas tanks in the early 20^th century to the use of hydrogen storage materials in the 21^st century. Perovskite hydrides based on light metal elements have been one of the promising materials for hydrogen storage due to their high gravimetric hydrogen capacity. Among these, magnesium-based perovskite hydrides, such as NaMgH₃, have been investigated extensively. However, poor hydrogen desorption kinetics and high operational temperature remain to be the challenge for its practical use.

The objective of this thesis was to study the possibility of modification of structural and functional properties induced by the use of high pressure on light hydrides crystallizing in the perovskite structure. In this study, the synthesis of several magnesium-based perovskite hydride like NaMgH₃ and KMgH₃, using high-pressure and high-temperature technique was performed. In-situ X-ray diffraction analysis revealed some information on the phase transformation occurring with the binary hydride precursors, as well as the synthesis mechanism at extreme conditions. Neutron powder diffraction studies at high-pressure performed at the Institut Laue-Langevin enabled the determination of mechanical properties (bulk modulus) of NaMgH₃ and KMgH₃.

Cation substitution at the A-site of the perovskite was also performed on NaMgH₃ to decrease its hydrogen desorption temperature. A lithium-substituted NaMgH₃ (Na_1-xLi_xMgH₃) was also synthesized at high-pressure. Differential Scanning Calorimetry revealed that the hydrogen desorption temperature of the Li-substituted NaMgH₃ is lower compared to the pure NaMgH₃, which confirmed a destabililization of the material via cation substitution. The reversibility of hydrogen desorption of the said materials is also confirmed by the calorimetric measurements.

During this thesis, we also tried to synthesize, without success, the compounds LiMgH₃ and NaCaH₃ although predicted as stable by studies based on theoretical calculations.

Overall, the investigation of these light magnesium-based perovskites paves the way to the engineering of hydrides with tailored hydrogen sorption properties.