Hydrogen storage on a star-like CBe₅Li₅+ superalkali cluster featuring planar pentacoordinate carbon

Abstract

The hydrogen storage capacity of the star-like planar pentacoordinate carbon (ppC) superalkali cluster CBe₅Li₅⁺, whose high stability can be understood through the 18-electron rule, was studied using density functional theory (DFT). The obtained results showed that H₂ adsorbs on the CBe₅Li₅⁺ cluster in molecular form, and the cluster remains planar and stable even after adsorption. Importantly, the CBe₅Li₅⁺ cluster is predicted to be a promising candidate for hydrogen storage material, achieving a gravimetric density of up to a theoretical limit of 25.8 %. Additionally, molecular dynamics (MD) simulations were performed on CBe₅Li₅⁺, 5H₂@CBe₅Li₅⁺, 10H₂@CBe₅Li₅⁺, 15H₂@CBe₅Li₅⁺, and 16H₂@CBe₅Li₅⁺ clusters at room temperature to study the adsorption and desorption of H₂ molecules over time. The MD simulations revealed that the majority of adsorbed hydrogen molecules shifted out of the cluster within 300 fs; however, some H₂ molecules remained bound to the cluster. In ADMP molecular dynamics simulations, H₂ was considered bound to the CBe₅Li₅⁺ cluster when the minimum H–cluster atom distance stayed under 2.5 Å. A distance exceeding 3.0 Å with continuous separation, lacking oscillations, signified desorption from the cluster surface. The energy analysis from MD simulations indicated that the structures are dynamically stable. Even after H₂ adsorption, the planarity of the CBe₅Li₅⁺ cluster is retained, confirming its stability. These findings suggest that CBe₅Li₅⁺ is a structurally strong and efficient candidate for next-generation hydrogen storage applications.