Unveiling Calcium-Decorated Psi-Graphene as a High-Capacity Hydrogen Storage Material: A First-Principles Investigation

Abstract

Our work investigates the potential of Ca-decorated Psi-Graphene for efficient hydrogen storage using first-principles electronic structure calculations and ab initio molecular dynamics simulations. The system exhibits an exceptional storage capacity of 13.44 wt% by adsorbing up to 82 H₂ molecules in a fully Ca loaded Psi-Graphene unit cell, significantly exceeding the Department of Energy (DOE) target. The last four hydrogen molecules of each single Ca atom have low binding energies under GGA approximation due to the only presence of Vander Waals interactions. The uniform binding energy of ~0.232 eV (under the GGA approximation) surpasses other Ca-decorated materials, attributed to H₂ polarization, hybridization of Ca 3d empty orbitals with H₂ σ orbitals, and the non-symmetric nature of Psi-Graphene. Additionally, strong Ca-substrate binding (~1.95 eV/atom) ensures system stability, as confirmed by density of states (DOS), projected density of states (PDOS), and Bader charge analysis. We have also performed Nudged Elastic Band (NEB) analysis to confirm that our system is not prone to metal clustering. The non-magnetic nature of isolated Ca and Psi-Graphene maintains a zero magnetic moment throughout the adsorption process. Ab initio molecular dynamics simulations further validate the thermal stability of the system up to 500 K. Using Van't Hoff equation, the desorption temperature falls within the range of 334.16–364.79 K between 5 and 12 bar pressure. These findings establish that Ca-decorated Psi-Graphene is a highly promising candidate for hydrogen storage applications.