Impact of Li Decoration on P-C3N Monolayer for Reversible Hydrogen Storage: A First-Principles Study

Two-dimensional carbon nitride materials have emerged as promising candidates for multifunctional applications. Motivated by the growing interest in carbon nitride-based two-dimensional materials, we investigated the hydrogen storage capacity of a Li-decorated P-C3N (Li@P-C3N) monolayer using density functional theory (DFT) calculations. Upon functionalization with Li atoms, the P-C3N monolayer can accommodate up to 12 H2 molecules, achieving a hydrogen storage capacity of 9.59 wt % with adsorption energies ranging from -0.18 to -0.13 eV per H2. The calculated material-level gravimetric capacity exceeds the numerical value of the DOE system-level gravimetric target. The hydrogen adsorption mechanism on Li@P-C3N was analyzed through charge transfer analysis, projected density of states (PDOS), and noncovalent interaction (NCI) analysis. The thermal stability of both pristine P-C3N and Li@P-C3N systems was examined using ab initio molecular dynamics (AIMD). Furthermore, the dynamical stability of Li@P-C3N was confirmed through phonon dispersion calculations. The reversibility of hydrogen adsorption in the Li@P-C3N + 12H2 system was also investigated using AIMD simulations. These results demonstrate that Li-decorated P-C3N is a highly efficient candidate for hydrogen storage. Therefore, experimental investigations of P-C3N are strongly encouraged to validate its potential for reversible hydrogen storage applications.