Penta-octagraphene (POG) is a newly suggested two-dimensional carbon allotrope recognized for its distinct configuration and fascinating electronic characteristics. This work presents a new inorganic counterpart of POG, named POG-B₄C₂N₃, designed through density functional theory (DFT) calculations. This new structure exhibits a direct band gap transition at the X-point, measured at 0.32/0.86 eV with PBE/HSE functionals. Mechanical properties were comprehensively assessed, showcasing its Young's modulus (Y_max/Y_min = 157.12/100.84 N/m) and shear modulus (G_max/G_min = 83.03/38.09 N/m), alongside Poisson's ratio (ν_max/ν_min = 0.58/-0.09), indicating that POG-B₄C₂N₃ is an auxetic material. Additionally, Li decoration on this monolayer was studied to investigate its potential to enhance hydrogen storage through physisorption. The Li@POG-B₄C₂N₃ system shows robust physisorption (adsorption energies ranging from -0.35 to -0.19 eV), high hydrogen storage capacity (8.35 wt %), and effective hydrogen desorption dynamics, positioning this novel material as a promising platform for reversible hydrogen storage.

A two-dimensional graphene-like carbon nitride (g-CN) monolayer decorated with the superatomic cluster NLi₄ was studied for reversible hydrogen storage by first-principles calculations. Molecular dynamics simulations show that the g-CN monolayer has good thermal stability at room temperature. The NLi₄ is firmly anchored on the g-CN monolayer with a binding energy of −6.35 eV. Electronic charges are transferred from the Li atoms of NLi₄ to the g-CN monolayer, mainly due to the hybridization of Li(2s), C(2p), and N(2p) orbitals. Consequently, a spatial local electrostatic field is formed around NLi₄, leading to polarization of the adsorbed hydrogen molecules and further enhancing the electrostatic interactions between the Li atoms and hydrogen. Each NLi₄ can adsorb nine hydrogen molecules with average adsorption energies between −0.152 eV/H₂ and −0.237 eV/H₂. This range is within the reversible hydrogen storage energy window. Moreover, the highest achieved gravimetric capacity is up to 9.2 wt%, which is superior to the 5.5 wt% target set by the U.S. Department of Energy. This study shows that g-CN monolayers decorated with NLi₄ are a good candidate for reversible hydrogen storage.