A Conceptional Constant-Pressure Integrated Hydrogen Purification And Storage System By Combining The Modified Graphene And Carbon Nanotube: A Molecular Dynamics Analysis

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 (Large-scale 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.