حســـــــاب خـــواص تـخزين الـهيدروجين في الـهيدريدات القائمة على Li وna المطعمة بــذرات (c,si, Ge)

Résumé: The aim of this work is to improve the hydrogen storage properties in lithium base hydrides and in sodium base hydrides. These improvements include increasing hydrogen storage and its reversibility, making it easier for hydrogen to enter and realize in these hydrides. For this purpose, it was studied structural and electronic properties of referential hydrides LiH and NaH, and super lattice hydrides Li7XH8 and Na7XH8 which introduce the atoms of C, Si and Ge at the position of X atom. This study was carried out using density functional theory (DFT), the linear augmentation plane waves method and full potential (FP-LAPW), implemented in the WIEN2k program. For Li7XH8 hydrides, a strong covalent bond was found along Li-(C, Si and Ge) and along Li-(C, Si and Ge) which decreases formation energy and dissociation heat values which leads to a decrease in the stability of super lattice hydrides Li7XH8 compared to the reference hydride LiH. The same result was observed for Na7XH8. Concerning Li7XH8 hydrides, it was found that Li7CH8 hydride has good hydrogen storage properties, represented by greater reversibility, higher storage density, smaller lattice constant and lower dissociation temperature compared to Li7SiH8 and Li7GeH8. Concerning Na7XH8 hydrides, it was found that Na7SiH8 hydride has good hydrogen storage properties, represented by greater reversibility, acceptable storage density and lower dissociation temperature compared to Na7CH8 and Na7GeH8. For fuel cell applications, the hydride Na7GeH8 is considered the best compared to Na7SiH8 and Na7CH8. The referential hydrides have an insulating character and the super lattice hydrides have a conductive character. The electronic study of referential hydrides and the super lattice hydrides confirms and supports the obtained results.

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