First-Principles Insights of Cr-Decorated BeN₄ Monolayer for Promising Hydrogen Storage

Hydrogen is widely recognized as a clean and sustainable energy vector and has been considered a potential alternative to traditional fossil-based energy sources. Recently, two-dimensional (2D) nanomaterials have attracted significant attention as effective candidates for enhancing hydrogen storage performance and practical applicability within the field of clean energy technologies. In this investigation, the hydrogen adsorption behavior of Cr-functionalized beryllium tetranitride (BeN₄) was systematically explored through density functional theory (DFT) calculations combined with van der Waals (vdW) corrections. The obtained theoretical results demonstrate that the dual-side Cr-modified BeN₄ monolayer is capable of accommodating as many as 18 hydrogen molecules, exhibiting a mean adsorption energy of approximately -0.12 eV, which yields a gravimetric hydrogen storage density of 9.06 wt %. This storage capacity is higher than the target proposed by the U.S. DOE and outperforms numerous previously reported two-dimensional hydrogen storage systems. The estimated desorption temperature (T_D = 155 K) is notably above the critical temperature of hydrogen. Ab initio molecular dynamics simulations conducted at 200 and 300 K further indicate rapid hydrogen desorption kinetics (τ = 1.08 × 10^-10 s), demonstrating the excellent reversibility of the adsorption-desorption process. In addition, the hydrogenated structure maintains its structural stability under ambient conditions, even at a relatively low pressure of 1.37 MPa, highlighting the promising capability of this system for efficient, reversible, and practical hydrogen storage.