Extensive Multiscale Investigations of Li/Na-Functionalized Three-Dimensional Borophosphene for Enhanced Hydrogen Storage

Three-dimensional porous borophosphene (3D-B 2 P 2 ) has emerged as a promising material for battery applications. Beyond this, its inherently porous crystal structure, along with excellent thermal and mechanical stability, suggests a broader potential. Therefore, in this work, we extend its application scope by systematically exploring its suitability for hydrogen storage using density functional theory (DFT) calculations and ab initio molecular dynamics (AIMD) simulations by exploiting the polarizing mechanism induced by alkali atoms. Particularly, our findings demonstrate that Li (−4.16 eV) and Na (−3.31 eV) bind strongly to 3D-B 2 P 2 driven by pronounced charge transfer. This phenomenon enables the polarization of up to five H 2 molecules per metal atom, yielding capacities of 7.07 and 6.36 wt %, meeting the DOE’s targets, with optimal average adsorption energies for reversible storage (−0.152 and −0.105 eV/H 2 ). Furthermore, the functionalized systems exhibit very low H 2 diffusion barriers (0.0056–0.12 eV) ensuring efficient kinetics. Pressure–H 2 capacity–temperature-dependent studies reveal that the Li-functionalized system achieves an effective, reversible gravimetric capacity of 5.74 wt % at 298.15 K and 46 bar, aligning with practical application requirements. AIMD simulations confirm stable hydrogen cycling under ambient conditions. Thus, experimental investigations of 3D-B 2 P 2 as a potential material for reversible H 2 storage are recommended.