Enhanced Reversible Hydrogen Storage Performance of Mg-Decorated g-C2N: First Principles Calculations

The graphene-like 2D material g-C2N owns superior properties for functional materials development, for instance, its ideal porosity can easily accommodate functional metal atoms, making itself more competitive for energy storage. In this study, density functional theory (DFT) computational studies were employed to solve the electronic structure of Mg-doped g-C2N, and furthermore its potential in hydrogen storage was systematically evaluated. Within our calculations, we found that partial charges of the doped Mg atoms can be successfully transferred to pyridinic N atoms. In one aspect, the Mg atoms can display higher electropositivity, and in another aspect, the N atoms own higher electronegativity. Such a change in electronic structure is favorable to enhance its hydrogen adsorption performance, as the H2 molecules in the vicinity of Mg and N atoms can be easily polarized, and thus the electrostatic attractions can be strengthened. In addition, multiple configurations of the Mg-doped g-C2N with adsorbed H2 molecules were presented also in this study, and we found that each 2 × 2 supercell unit possesses a high gravimetric surface area of 2863 m2/g, and can accommodate at most 44 H2 molecules with the adsorption energies ranging from −0.29 eV to −0.12 eV. With the decoration of Mg, its capacity of hydrogen storage can be as high as 8.03 wt%. The theoretical analysis presented in this study provides important chemical insights for energy materials design, with profound implications for improving the performance of 2D materials’ hydrogen.