The use of lithium-decorated phosphorene for hydrogen storage is significantly limited due to metal aggregation on substrates. Despite considerable research and effort in the literature to address this issue, no one has succeeded in enhancing the capacity of phosphorene through metal atom decoration. Based on density functional theory (DFT) and AIMD simulations, superalkali NLi4-decorated black phosphorene monolayer is developed as a new hydrogen storage solid-state material. Our results show that the NLi4-cluster exhibits a significant binding energy of −3.18 eV when attached to one side of the phosphorene on a stable site, indicating a strong affinity between the NLi4-cluster and phosphorene surfaces. Moreover, 2(NLi4)@phosphorene can store up to 30H2 molecules with a suitable average hydrogen adsorption-energy and a maximum hydrogen storage capacity of 6.8 wt%. Using the van't Hoff equation and increasing the pressure, we find that the desorption temperature is higher than the critical point for hydrogen. AIMD simulations at different temperatures demonstrate the thermal stability of the hydrogenated 2(NLi4)@phosphorene and the H2 desorption process. The findings of the present study suggest the potential utilization of the 2(NLi4)@phosphorene adsorptive material for hydrogen storage applications.