Li4B8H8 as a reversible hydrogen storage unit in free and graphene-anchored forms.

Hydrogen storage remains a major bottleneck for the deployment of hydrogen-based energy technologies, as conventional approaches such as high-pressure compression and cryogenic liquefaction impose high energy penalties, safety risks, and demanding infrastructure. Solid-state materials offer a safer and more reversible alternative, yet no existing system simultaneously satisfies the U.S. DOE targets of moderate adsorption enthalpy (-0.1 to -0.6 eV per H2), fast kinetics, and gravimetric capacities above 5 wt%. Here, we propose the Li4B8H8 cluster as a lightweight, electronically robust hydrogen-storage unit based on a nido-B8H84- borane framework functionalized by four exposed Li+ centers. Global potential-energy-surface searches and ab initio molecular dynamics identify a C2v global minimum for the isolated Li4B8H8 cluster. Extended-Lagrangian ADMP simulations reveal that the cluster is kinetically persistent up to 800 K, with the nido-B8H8 backbone remaining structurally intact. Beyond this temperature, at 1000 K, the high mobility and rearrangement of the Li centers compromise the structural integrity of the borane framework. Stepwise adsorption calculations reveal reversible coordination of up to 20H2 molecules with average adsorption energies BSSE-corrected of -0.17 to -0.09 eV per H2, yielding a gravimetric capacity of 24.8 wt% in the free cluster. When immobilized on graphene, Li4B8H8 maintains efficient storage performance, accommodating 16, 20, and 24H2 molecules at 5.9, 7.4, and 8.7 wt%, respectively, with adsorption energies consistently within -0.13 to -0.10 eV per H2, and retaining fully physisorptive character as confirmed by IGMH interaction analysis. These results establish Li-decorated nido-boranes as a previously overlooked class of molecular hydrogen sorbents, extending cluster-based design strategies beyond conventional B6-derived motifs and offering a promising route toward high-capacity, intermediate-binding solid-state hydrogen-storage media.