Enhanced H2 storage in silicene through lithium decoration and single vacancy and Stone-Wales defects: A density functional theory investigation

Abstract

Defect engineering and metal decoration onto 2-D materials have gained major attention as a means of creating viable hydrogen storage materials. This Density Functional Theory (DFT) based study presents lithium decorated single vacancy (SV) and Stone-Wales (SW) defective silicene as a viable media for storing hydrogen via physisorption. Introducing defects increases the Li adatom's binding energy from −2.36 eV in pristine silicene to −3.44 and −2.73 eV in SV and SW silicene, respectively, preventing Li adatom clustering. The presence of defects and Li adatom further aid hydrogen adsorption onto the substrates with binding energies present between the US-DOE set range of −0.2 to −0.7 eV/H₂ with the highest binding energy measured to be −0.389 eV/H₂. The enhanced H₂ binding energies are a result of a combined contribution of the Li(p) and Li(s) orbitals with the H(s) orbital with an indirect electronic transfer from the silicene substrate to the Li adatom. Upon double side Li decoration, both the Li-decorated defective systems were able to effectively store multiple H₂ molecules up to 28 H₂ with the highest gravimetric density being 5.97 wt%. Ab Initio molecular dynamic simulations conducted at 300 K and 310 K confirm the stability of the Li adatom as well as the adsorbed H₂ molecules at room temperature and establish the viability of these systems as effective, high gravimetric density, physisorption-based hydrogen storage media.