Hydrogen adsorption and diffusion through a two dimensional sheet of lithium: a first principles study

Two-dimensional (2D) materials have shown promise as highly selective, ultrathin membranes to transport ions, and atomic and subatomic particles. They have also been regarded as potential hydrogen storage candidates due to their chemical stability and high specific surface area. However, most of these studies have been carried out with semiconducting 2D materials. With recent explorations towards the existence and stability of 2D metals, we explore the hydrogen adsorption and diffusion through a 2D metallic sheet of lithium. We report that in the lowest energy metallic configuration, the sheet is predicted to crystallize in a highly buckled honeycomb structure. We calculate the adsorption energy for the diffusion of hydrogen on various high symmetry sites in the lattice, and find that adsorption is energetically favoured. We study the minimum energy pathways for diffusion through the sheet and find that the lowest energy barriers exist for tunneling through the honeycomb ring. Our results would be of direct technological relevance to the applications of 2D metallic nanostructures as membranes for selective transport or towards storage.