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

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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...