Hydrogen storage in Li decorated and defective pentaoctite phosphorene: A density functional theory study

Abstract

Hydrogen storage in 2D pentaoctite phosphorene was investigated by density functional theory (DFT) calculations. Defect engineering and Li decoration were adopted to evaluate their effects on the hydrogen storage. The formation energies for two types of point defects, single vacancy (SV) and double vacancy (DV) were calculated. The DFT results showed that pristine pentaoctite had a very weak binding with H2 molecule. With the defect formation energies in the order of black phosphorene, the point defects marginally improved the binding energy of H2 molecule. However, Li decoration over pristine and defective substrates enhanced the binding energy of H2 molecule by 5–10 fold improving from around −0.03 eV/H2 to −0.25 eV/H2, thereby, resulting a better H2 storage capacity. PDOS calculation evidenced the charge transfer from Li atom as its key attribute. In addition, multiple Li adatoms were decorated over the substrate at the favorable sites. In Li decorated pristine, SV, and DV defective substrates, up to 5, 6, and 3 H2 molecules could be absorbed at each Li adatom. The diffusion energy barrier of Li from one favorable site to another was calculated to be an order of magnitude higher that its thermal energy causing an impedance to clustering.