Hydrogen Storage on a New 2D Orthorhombic Boron Nitride Allotrope: Insights from Density Functional Theory

Hydrogen is a clean and renewable energy carrier, but its reversible storage near ambient conditions remains a major challenge. Here, density functional theory (DFT) combined with ab initio molecular dynamics (AIMD) is employed to assess the newly predicted 2D orthorhombic diboron dinitride (o-B₂N₂) monolayer, in pristine and Li-functionalized forms, as a hydrogen storage medium. On the pristine surface, H₂ physisorbs with binding energies of -0.158 to -0.174 eV. Li atoms anchor strongly at the hexagonal hollow sites (Ebind from -0.979 to -1.321 eV, strongest at the B-rich H1 site), donate 0.65-0.84 |e| to the substrate, and render the semiconducting monolayer metallic. A positive cluster formation energy (+0.171 eV per Li pair) and a 5 ps AIMD simulation at 400 K confirm that the Li adatoms remain dispersed, without clustering. Each Li+ center polarizes and binds up to five H₂ molecules, with average adsorption energies of -0.207 to -0.336 eV/H₂, within the optimal window for room-temperature reversible storage. The 4Li@o-B₂N₂(20H₂) system attains a theoretical gravimetric capacity of 15.12 wt% and a practical capacity of 10.99 wt% under realistic operating conditions (charging at 30 atm/25 °C; release at 3 atm/100 °C). These results establish Li-functionalized o-B₂N₂ as a promising hydrogen storage material that merits experimental exploration.