Hydrogen storage performance of the TPO-graphene system: first-principles calculations

Among the many forms of graphene and its derivatives, TPO-graphene (TPOG) exhibits good thermodynamic and mechanical stability and uniform pore size, making it a promising candidate for hydrogen storage. In this study, we systematically analyze the hydrogen storage performance and adsorption mechanism of the TPOG system using first-principles calculations. It was found that Li and Na atoms could be stably bound to the TPOG substrate, with the metal atoms transferring a significant amount of charge to the substrate and thereby generating an electric field directed toward the substrate. Adsorption calculations revealed that the 2Li@TPOG system adsorbs 8 H₂ molecules, corresponding to a hydrogen storage capacity of 10.7 wt%, while the 2Na@TPOG system adsorbs 12 H₂ molecules, with the hydrogen storage capacity reaching 12.7 wt%. The adsorption mechanism of H₂ molecules predominantly involves two distinct pathways: strong polarization induced directly by the internal electric field, resulting in an average adsorption energy of -0.303 eV; and weak polarization arising from the electric field of previously polarized H₂ molecules, which induces intermolecular van der Waals interactions, with an average adsorption energy of about -0.120 eV. Molecular dynamics (MD) simulations further confirmed that at 300 K, the 2Li@TPOG and 2Na@TPOG systems retained hydrogen storage capacities of 8.3 wt% and 8.9 wt%, respectively, significantly exceeding the U.S. Department of Energy (DOE) target and demonstrating their promise as room-temperature hydrogen storage materials.