Hydrogen storage performance of TPO-Graphene system: first-principles calculations

Abstract

Among the many forms of graphene and its derivatives, TPO-Graphene (TPOG) exhibits good thermodynamic, mechanical stability and uniform pore size, making it a promising candidate for hydrogen storage. In this paper, 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 bind to the TPOG substrate, with the metal atoms transferring significant 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 a 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.