The Open-Access Journal for the Basic Principles of Diffusion Theory, Experiment and Application Molecular dynamics investigation of the transport of hydrogen in ZIF-7

The importance of hydrogen-based clean energy systems due to the global climate change, air pollu-tion and energy security has lead to several studies of hydrogen production, separation and storage in industry and science [1, 2]. In the current study, we have investigated the diffusion of hydrogen within a novel Zeolitic imidazolate framework (ZIF-7, Figure 1a). ZIFs are a subfamily of porous metal-organic frameworks (MOFs) [3, 4]. For investigating diffusion behavior of hydrogen in this lattice, we have applied Molecular Dynamics (MD) simulations. At the studied temperatures in a series of MD simulations performed with a rigid lattice, no diffusion of any gas was observed in ZIF-7. The same behavior has been reported by A. Battisti et al. [5]. Applying the flexibility to the framework, the measured diffusion coefficient for hydrogen was about 2.7 × 10−9 m2 s−1 while nearly no diffusion was observed for any other studied gas in ZIF-7. These results clearly elucidate the molecular sieving behavior of this material for hydrogen reported by Caro et al. and represent it as a promising membrane in this domain which is due to its very small pore structure and window size (0.3 nm) that is close to the kinetic size of the hydrogen molecul