Reversible hydrogen storage via Ca-decorated T-C₃N monolayer: insights from first-principles calculations

Two-dimensional carbon-based materials have emerged as promising candidates for solid-state hydrogen storage. In this work, the hydrogen storage performance of T-C₃N monolayer functionalized with calcium atoms is systematically investigated using first-principles calculations. Calcium functionalization on T-C₃N exhibits high binding energy and excellent thermal stability, as confirmed by ab initio molecular dynamics (AIMD) simulations. Upon Ca decoration, the T-C₃N system undergoes a transition from semiconducting to metallic behavior and acquires a finite magnetic moment, as revealed by spin-polarized band structure calculations. The results demonstrate that the Ca@T-C₃N system can adsorb up to 16 H₂ molecules, achieving a gravimetric hydrogen storage capacity of 9.15 wt%, which exceeds the U.S. Department of Energy (DOE) target. The hydrogen adsorption energy lies within the optimal range of -0.12 to -0.20 eV per H₂. The hydrogen adsorption mechanism is elucidated through Bader charge analysis, charge density difference (CDD) plots, and projected density of states (PDOS) calculations. The thermal stability and reversibility of hydrogen storage in the Ca@T-C₃N system are further validated by AIMD simulations. Overall, these findings establish Ca@T-C₃N as a highly efficient and reversible hydrogen storage material for light-duty fuel cell vehicles and provide theoretical insights that may inspire future experimental exploration of calcium-decorated T-C₃N monolayers.