Mg 2 FeH 6 , a potential hydrogen storage medium with the largest volumetric hydrogen capacity known, is mostly obtained by reacting the 2Mg−Fe mixture with hydrogen through mechanical alloying methods. However, these mechanical alloying methods for generating Mg 2 FeH 6 are inconvenient in operation, and the mechanism of formation of Mg 2 FeH 6 behind these methods is not clear so far. In this study, through molecular dynamics simulations, the microscopic process of the chemical reaction between the 2Mg−Fe mixture and hydrogen to produce Mg 2 FeH 6 was investigated to clarify the mechanism of hydrogen adsorption by the 2Mg−Fe mixture. By analyzing the changes in bond energy and potential energy of the system, as well as the atomic trajectory, the breaking and re-formation of chemical bonds are clarified, which indicates the microscopic mechanism of hydrogen adsorption by the 2Mg−Fe mixture. In addition, the influences of temperature and pressure on the hydrogen adsorption process of the 2Mg−Fe mixture were studied. It was shown that increasing the pressure has a positive effect on the hydrogen storage capacity of the 2Mg−Fe mixture, while increasing temperature beyond 300 °C has little effect. Especially, the mass hydrogen storage capacity of the 2Mg−Fe mixture at 10 MPa and 400 °C was found to reach its theoretical hydrogen storage capacity of 5.5 wt %.
A large-capacity hydrogen storage system, which is also able to purify the hydrogen during storage, is appealing and bears significance for the mobile hydrogen use systems which require highly pure hydrogen, since it improves the adaptability of these systems to hydrogen fuels of different purity grades. Inspired by the fact that carbon nanotubes (CNTs) and nanoporous graphene (NPG) membranes have the ability to adsorb and separate gases, respectively, a concept for a constant-pressure integrated hydrogen purification and storage system composed of these two carbon-based materials is proposed. In this integrated system, hydrogen is stored by the adsorption of CNTs and purified by the two-layer nanoporous graphene membranes during the permeation driven by hydrogen concentration difference at constant pressure. The molecular dynamics simulation for the purification and storage processes was carried out with the open source software LAMMPS (Largescale Atomic/Molecular Massively Parallel Simulator), by which the purification efficiency and hydrogen storage capacity under different working conditions were investigated. The results showed that the preferable working parameters for the purification and storage processes are different, and thus the determination of theses parameters should strike a balance between their effects on both storage and purification processes. Through comparative studies, it was found that the system can obtain the best performance of purification and hydrogen storage at the feed-hydrogen temperature, adsorption temperature, and working pressure of 300 K, 60 K, and 15 MPa, respectively, with the storage density and hydrogen purity of 4.57 wt % and 95% (75% before purification), respectively. The integrated hydrogen storage and purification system proposed in this paper, although just a concept, can provide a theoretical reference for designing large-capacity hydrogen storage systems for equipment which requires highly pure hydrogen.
Summary Graphynes are potential hydrogen storage materials due to their unique acetylene bond structure (C‐C ≡ C‐C), and can be classified into α‐GY, β‐GY, γ‐GY, σ‐GY, GDY, etc., according to the proportion of their involved acetylene bonds. To enhance their hydrogen storage capacities, four typical graphynes (α‐GY, β‐GY, δ‐GY, and GDY) were modified by a joint Na‐decoration and B‐doping technique in this research, and the hydrogen adsorption processes of these modified graphynes were investigated by molecular dynamics simulation to clarify the effects of the structure modification on their hydrogen storage capacities. The results showed that the hydrogen storage capacities of the modified graphynes are larger than those of non‐modified graphynes, and that the joint Na‐decorated and B‐doped α‐GY obtains the largest hydrogen storage capacity of 9.41 wt%. The mechanism of the enhancement of hydrogen storage by the joint Na‐decoration and B‐doping was found to be that the Na‐decoration and B‐doping strengthen the adsorption energy between acetylene bonds and hydrogen atoms. Since the modified α‐GY has satisfactory hydrogen storage capacity, far exceeding the target set by the U.S. Department of Energy (DOE) in 2020 for portable hydrogen storage system, it can be expected to be a potential hydrogen storage material in the future.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.