Revealing enhancement mechanism of volumetric hydrogen storage capacity of nano-porous frameworks by molecular simulation

摘要

In the past decade, nano-porous frameworks (NPFs) have been rapidly developed and considered as the most promising hydrogen storage materials, due to their unique high surface areas and high pore volumes. However, the development and design of NPFs with balanced gravimetric and volumetric H-2 storage capacities are still facing a challenge. In this work, 103 porous materials with 34 topologies promising for application in hydrogen storage were theoretically constructed by using experimentally available organic linkers and geometrically optimized further on the basis of molecular mechanics and density functional theory. They were then computationally screened using the grand ensemble Monte Carlo (GCMC) simulations to search the optimal candidates for hydrogen storage under specific conditions. The seven selected NPFs such as SRS-PAF-1 with high-performance hydrogen storage were evaluated and identified on the basis of gravimetric and volumetric H-2 storage capacity. Based on univariate analysis, we examined the relationship between the structural characteristics of all these NPFs and their hydrogen storage capacity, and elucidated the correlations between the structural descriptors (phi, rho, V-p, LCD, PLD, GSA, and VSA) by the principal components analysis. Compared with the benchmark MOFs such as NU-1103, SNU-70 and PCN-610, SRS_PAF-1 exhibit the balanced deliverable gravimetric and volumetric H2 storage capacity of 21.8 wt% and 38.0 g L-1, respectively. BOR-TTEI exhibits the highest gravimetric hydrogen storage capacity of 11.3 wt% at ambient temperature and 100 bar. Moreover, PCN-250 and PPN-6 were taken as examples to investigate the enhancement effect of powder compression and network interpenetration on volumetric hydrogen storage performance (N-v) of NPFs. The results indicate that powder compression can efficiently improve their N-v, but the effect of network interpenetration on N-v depends on the length of the organic linker. In a word, those molecular insight into the relationship between the structural characteristics of NPFs and hydrogen storage capacity will help experimental chemists design and synthesize new NPFs with high-performance for hydrogen and other gas storage. (C) 2020 Elsevier Ltd. All rights reserved.