Sodium-Decorated P-C3N: A Porous 2D Framework for High-Capacity and Reversible Hydrogen Storage

The development of reversible hydrogen storage materials has become crucial for enabling carbon-neutral energy systems. Based on this, the present work investigates the hydrogen storage on the sodium-decorated P-C$_3$N (Na@P-C$_3$N), a porous carbon nitride monolayer recently proposed as a stable semiconductor. First-principles calculations reveal that Na atoms preferentially adsorb with an adsorption energy of -4.48~eV, effectively suppressing clusterization effects. Upon decoration, the system becomes metallic, while \textit{ab initio} molecular dynamics simulations confirm the thermal stability of Na@P-C$_3$N at 300~K. Hydrogen adsorption on Na@P-C$_3$N occurs through weak physisorption, with energies ranging from -0.18 to -0.28~eV, and desorption temperatures between 231 and 357~K. The system can stably absorb 16 H$_2$ molecules per unit cell, corresponding to a gravimetric storage capacity of 9.88~wt\%, surpassing the U.S. Department of Energy target. These results demonstrate that Na@P-C$_3$N is a promising candidate for lightweight, stable, and reversible hydrogen storage.