In this study, we studied defect-engineering and lithium decoration of 2D phosphorene for effective hydrogen storage using density functional theory. Contrary to graphene, it is found that the presence of point-defects is not preferable for anchoring of H-2 molecules over defective phosphorene. According to previous research, strategies such as defect engineering, metal decoration, and doping enhance the hydrogen storage capacity of several 2D materials. Our DFT simulations show that point defects in phosphorene do not improve the hydrogen storage capacity compared to pristine phosphorene. However, selective lithium decoration over the defective site significantly improves the hydrogen adsorption capacity yielding a binding energy of as high as -0.48 eV/H-2 in Li-decorated single vacancy phosphorene. Differential charge densities and projected density of states have been computed to understand the interactions and charge transfer among the constituent atoms. Strong polarization of the H-2 molecule is evidenced by the charge accumulation and depletion. The PDOS shows that the presence of Li leads to enhanced charge transfer. The maximum gravimetric density was investigated by sequentially adding H-2 molecules to the Li-decorated single vacancy defective phosphorene. The Li-decorated single vacancy phosphorene is found to possess a gravimetric density of around 5.3% for hydrogen storage. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.