Efficient Hydrogen Storage in Superalkali NLi₄-Decorated Boron Phosphide Biphenylene

Two-dimensional porous materials are potential candidates for reversible hydrogen storage. Driven by the growing popularity of organic biphenylene materials, we explored the hydrogen storage capacity of superalkali NLi4-decorated boron phosphide biphenylene (BPB) using first-principles calculations employing the GGA-PBE functional enhanced with van der Waals corrections. Interestingly, NLi4 was strongly bonded with the BPB monolayer via an electronic charge transfer mechanism with a large binding energy of −5.38 eV when decorated on one side and −5.34 eV/NLi4 when decorated on both sides of the monolayer. The NLi4@BPB complex can adsorb up to 16 H2 molecules, and the 2NLi4@BPB complex adsorbs a maximum of 32 H2 molecules with the H2 adsorption energy ranging from −0.35 to −0.24 eV/H2, resulting in a hydrogen storage capacity of 5.6 and 9.93 wt %, respectively, surpassing the DOE target of 5.5 wt %. H2 interacts with Li atoms in NLi4 clusters by charge polarization, which causes lengthening of the H–H bond. The hydrogen occupation index evaluated for various temperatures and pressures reveals, about the hydrogen reversibility, that the material offers complete desorption above 380 K at 1 atm. Ab initio molecular dynamics simulations further confirm the structural stability and the reversibility of hydrogen adsorption. From the findings, NLi4-decorated BPB proved to be a very efficient hydrogen storage material.