First-principles prediction of Mg decoration on monolayer g-C6N7 as a promising a hydrogen storage media

In recent years, two-dimensional materials with larger specific surface area and more active sites have been widely designed as hydrogen storage materials. In this paper, we investigate and clarify the hydrogen storage performance of Mg-decorated g-C6N7 (Mg@g-C6N7) monolayer using first-principles calculations. By calculating the binding energy, we find that the most stable configuration for the Mg atom is at the holey site bonded with two N atoms (denoted as N1) in monolayer g-C6N7. A modification effect of the Mg atom enhances the activity of g-C6N7 monolayer. The ideal theory storage gravimetric density of the Mg@g-C6N7 monolayer is up to 10 wt% with the average adsorption energy of −0.178 eV/H2. Furthermore, the physical mechanism of H2 molecules adsorbed on monolayer Mg@g-C6N7 is theoretically explored. We find that orbital interactions and electrostatic interactions exist between Mg2+ cation and the 1st to 4th H2 molecules, while only strong electrostatic interactions make the 5th to 10th H2 molecules bind onto the Mg2+ cation. The effects of temperature and pressure on the hydrogen storage performance are also investigated, and the results show that the hydrogen adsorbed structures of Mg@g-C6N7 are stable at room temperature under mild pressure.