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

Sonai Seenithurai,Jeng-Da Chai

doi:10.1038/srep33081

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.

Highlights

In this work, we adopt dispersion-corrected TAO-DFT38 to study the electronic and hydrogen storage properties of Li-adsorbed n-acenes with various chain lengths (n = 3–8)
In 2015, the United States Department of Energy (USDOE) set the 2020 target of 5.5 wt% and the ultimate target of 7.5 wt% for the gravimetric storage capacities of onboard hydrogen storage materials for light-duty vehicles[8]
We have studied the electronic properties of zigzag graphene nanoribbons (ZGNRs) using thermally-assisted-occupation density functional theory (TAO-DFT), where the strong static correlation effects have been properly described[39]

Summary

Introduction

In this work, we adopt dispersion-corrected TAO-DFT38 to study the electronic and hydrogen storage properties of Li-adsorbed n-acenes with various chain lengths (n = 3–8). N-acene can strongly bind the Li adatoms with the binding energy range of 86 to 91 kJ/mol per Li. At the ground-state (i.e., the lowest singlet state) geometry of pure/Li-adsorbed n-acene, containing N electrons, the vertical ionization potential IPv =EN−1 −EN, vertical electron affinity EAv =EN −EN+1, and fundamental gap Eg =IPv −EAv =EN+1 +EN−1 − 2EN are obtained with multiple energy-difference calculations, where EN is the total energy of the N-electron system.

Results

Conclusion