Multiscale Study of Hydrogen Adsorption, Diffusion, and Desorption on Li-Doped Phthalocyanine Covalent Organic Frameworks

• Published in: Journal of physical chemistry. C Vol. 116; no. 30; pp. 15908 - 15917
• Main Authors: Guo, Jing-Hua, Zhang, Hong, Liu, Zhi-Pan, Cheng, Xin-Lu
• Format: Journal Article
• Language: English
• Published: Columbus, OH American Chemical Society 02.08.2012
• Subjects: Applied sciences; Chemical and electrochemical properties; Condensed matter: structure, mechanical and thermal properties; Diffusion in solids; Energy; Energy. Thermal use of fuels; Exact sciences and technology; Materials and auxiliary equipments used in energy engineering; Metals. Metallurgy; Physics; Solid surfaces and solid-solid interfaces; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties); Transport properties of condensed matter (nonelectronic); Metal organic framework; Monte Carlo method; Hydrogen storage; Adsorption energy; Adsorption site; Solubility; Desorption; Surface structure; Phthalocyanine; Lithium addition; Adsorption; Binding energy; Diffusion barrier; Density functional method; Diffusion process; Adsorption structure; Beryllium addition; Numerical simulation; Kinetics; Gas phase; Diffusion
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/jp305949q

In this paper, we performed a multiscale study on the hydrogen storage capacity of Li-doped phthalocyanine covalent organic frameworks (Li-doped Pc-PBBA COF). We combine the first-principles studies of hydrogen adsorption and migration energies with the kinetic Monte Carlo simulations of hydrogen adsorption, diffusion, and desorption processes in Li-doped Pc-PBBA COF. The first-principles calculations revealed that the Li atoms can be doped on the surface of the channel of Pc-PBBA COF with a binding energy of 1.08 eV. Each Li cation can bind three H2 molecules with an average adsorption energy of 0.11 eV. At most, 24 H2 molecules can be adsorbed in one formula unit, corresponding to a maximum of gravimetric density of 5.3 wt % and volumetric uptake of 45.2 g/L. The diffusion barriers of H2 between different Li-adsorption sites are in the range 0.027–0.053 eV. The KMC simulations have predicted that the optimum conditions of hydrogen storage for Li-doped Pc-PBBA COF are at T = 250 K and P = 100 bar, with a gravimetric density of 4.70 wt % and volumetric uptake of 40.23 g/L. At T = 300 K and P = 1 bar, the adsorbed H2 molecules have fast desorption kinetics, and 97% hydrogen can be released from the adsorbed phase to the gas phase. A two-step modification method (the B-substitution is first) was also advanced to suppress the Li clustering behavior and further improve the binding energy of H2 molecules to doped Li atoms.