Effect of Li Adsorption on the Electronic and Hydrogen Storage Properties of Acenes: A Dispersion-Corrected TAO-DFT Study

Abstract

Due to the presence of strong static correlation effects and noncovalent interactions, accurate prediction of the electronic and hydrogen storage properties of Li-adsorbed acenes with n linearly fused benzene rings (n = 3–8) has been very challenging for conventional electronic structure methods. To meet the challenge, we study these properties using our recently developed thermally-assisted-occupation density functional theory (TAO-DFT) with dispersion corrections. In contrast to pure acenes, the binding energies of H2 molecules on Li-adsorbed acenes are in the ideal binding energy range (about 20 to 40 kJ/mol per H2). Besides, the H2 gravimetric storage capacities of Li-adsorbed acenes are in the range of 9.9 to 10.7 wt%, satisfying the United States Department of Energy (USDOE) ultimate target of 7.5 wt%. On the basis of our results, Li-adsorbed acenes can be high-capacity hydrogen storage materials for reversible hydrogen uptake and release at ambient conditions.

Effect of Li Termination on the Electronic and Hydrogen Storage Properties of Linear Carbon Chains: A TAO-DFT Study

“…Among them, Li adsorption is especially attractive, because of its light weight with which a high gravimetric storage capacity could be easily achieved. Note also that Li-adsorbed carbon materials have been shown to possess relatively high gravimetric storage capacities with enhanced H 2 adsorption binding energies [9][10][11][12][13][14], through a charge-transfer induced polarization mechanism [2,[15][16][17].…”

“…Besides, existing XC density functionals in KS-DFT may also be adopted in TAO-DFT. Due to its computational efficiency and reasonable accuracy for large systems with strong static correlation, TAO-DFT has been successfully applied to the study of several strongly correlated electron systems at the nanoscale [14,[49][50][51], which are typically regarded as "challenging systems" for traditional electronic structure methods (e.g., KS-DFT with conventional XC density functionals and single-reference ab initio methods) [44]. Accordingly, TAO-DFT can be an ideal theoretical method for studying the electronic properties of Li 2 C n .…”

Electronic and Hydrogen Storage Properties of Li-Terminated Linear Boron Chains Studied by TAO-DFT

“…Here, we assess the multi-reference character of Li 2 B n by calculating the symmetrized von Neumann entropy 47 , 48 , 53 , 55 – 57 , 60 for the ground state of Li 2 B n . In Eq.…”

“…Note that Eq. ( 9 ) is the van’t Hoff equation 55 , 57 , 63 , 64 , where E b (H 2 ) is calculated using Eq. ( 7 ).…”

“…Moreover, TAO-DFT reduces to KS-DFT when the static correlation energy of a system is insignificant, enabling a well-balanced description for both systems possessing non-radical character and systems possessing radical character 53 – 57 . In our previous TAO-DFT studies, Li-adsorbed acenes 55 and Li-terminated linear carbon chains (Li 2 C n ) 57 were found to be promising HSMs at near-ambient conditions, showing that the search for promising HSMs can be extended to large systems possessing radical character. Although Li 2 C n and Li 2 B n look similar in structure, their electronic and hydrogen storage properties are distinctly different.…”