Density functional theory investigation of hydrogen storage properties on Mg-decorated tri-graphene

The excessive consumption of fossil fuels has led to energy shortages and environmental issues, thereby driving the development of efficient solid-state hydrogen storage materials. In this work, density functional theory (DFT) calculations were performed to systematically investigate the structural stability, electronic properties, and hydrogen storage properties of Mg-decorated tri-graphene (Tri-G), which is identified as a two-dimensional carbon material exfoliated from the [110] crystal plane of T-carbon. The results show that Mg atoms preferentially adsorb at the center of the dodecagonal ring (denoted as the H1 site), where approximately 1.38 e of the two valence electrons are transferred to the substrate, thereby forming positively charged active centers. The average adsorption energies of the first ten H 2 molecules fall within the ideal reversible range of −0.1 to −0.6 eV, while that of the 11th H 2 molecule is slightly above −0.1 eV, yet the molecule remains stably adsorbed. A single side of Mg@Tri-G can accommodate up to 11 H 2 molecules, while a double-sided configuration accommodates a total of 22 H 2 molecules, corresponding to a theoretical gravimetric hydrogen storage capacity of 12.43 wt%. The desorption temperatures are estimated via the van 't Hoff equation and range from 114 to 352 K, which are all well above the critical point of H 2 (33 K), suggesting reversible hydrogen uptake and release. Although the average adsorption energy of the fully loaded system (-0.089 eV) slightly exceeds the ideal threshold, the majority of the adsorbed H2 molecules remain within the reversible adsorption window, indicating good practical reversibility. This study provides a theoretical foundation for the design of low-cost, high-capacity two-dimensional carbon-based solid-state hydrogen storage materials.