Development And Application Of Hydrogen Storage Properties Of Li-N-H Materials

Low carbon, renewable hydrogen gas fuelled vehicles expected to mitigate the consumption of fossil fuel and help to improve the greenhouse effect. However, there are still many problems need to be resolved if we hope to make commercial use of hydrogen in a real sense. Among them, the core issue is how to effectively carry out the hydrogen storage. As compared with conventional methods, solid-state hydrogen storage has high energy density and safety during storage and transportation. In recent years, the solid-state hydrogen storage systems composed of light elements have been extensively investigated by many scholars, because all aspects of their hydrogen storage performance are excellent. Among them, the study of Li-N-H system is relatively popular.In this paper, different types of additives were doped into the LiH-NH3 and Li3N hydrogen storage system by a mechanical milling method, respectively. Then, we systematically studied how the types and content changes of additives can improve the kinetics, components, surface morphology and cycle performance of samples. At the same time, they were characterized and tested by means of powder X-ray diffraction, IR, TG-MS, PCT and BET method.Firstly, the hydrogen desorption properties for the reactions between MNH2-added (M= Li, Na, and K) lithium hydride and NH3 were systematically investigated. It is found that all of the 1 mol% alkali metal amide additives can improve the hydrogen desorption yield of the LiH-NH3 system, among which, LiNH2 shows the best effect. As compared to the other LiNH2-added composition, the 1 mol% LiNH2-added composition shows the best effect on improving the desorption kinetics of the LiH-NH3 system. Finally, according to the higher activation energy analysis, it is proposed that the effect of LiNH2 on the hydrogen desorption kinetics would be mainly due to physical effect including the formation of smaller grains or cleaner surface.Furthermore, the impact of multi-walled carbon nanotubes additive on the hydrogen storage properties of Li3N has been also systematically studied. As shown in the scanning electron microscopy and full bore analysis results, the multi-walled carbon nanotubes additive can reduce the particle size of Li3N samples and obtain a better dispersion. In a further study, we found that multi-walled carbon nanotubes can also increase the hydrogenation/dehydrogenation rate and decrease the peak hydrogen desorption temperature for this system. The enhancement of hydrogen storage performance becomes clearer and clearer with the increase of the multi-walled carbon nanotubes additive. Finally, the hydrogenation-dehydrogenation cycles data shows that multi-walled carbon nanotubes can significantly enhance the reversible stability of Li3N hydrogen storage system, when compared to the non-doped sample. Therefore, the mixture of Li3N with multi-walled carbon nanotubes results in an excellent hydrogenation/dehydrogenation property.