Reversible hydrogen storage properties of defect-engineered C₄N nanosheets under ambient conditions

Inspired by the promise of hydrogen (H₂) as a clean alternate to the existing energy sources, we have employed spin-polarized density functional theory calculations on a recently designed two-dimensional C₄N monolayer as a promising H₂ storage material. By means of first principles DFT calculations, we have comprehensively studied the geometric and electronic properties of pristine, defected and metal-doped C₄N nanosheets and further explored their H₂ storage properties. We found that light metal dopants such as Li, Na, K, Mg, and Ca bind strongly to defects on a C₄N nanosheet with binding energies of 3–4 eV per dopant. These binding energies are sufficiently strong to surpass metal clustering. Thermal stability of the metal-doped C₄N nanosheets has been further verified by means of ab initio molecular dynamics simulations. The bonding nature of the metal dopants with the C₄N nanosheet has been studied through Bader analysis and Roby-Gould methods and the electronic properties were studied through density of states. We found that each dopant in the metal-doped C₄N nanosheet can bind up to five H₂ molecules with adsorption energies ranging between 0.15 and 0.60 eV/H₂, which results in optimal H₂ storage capacities. Finally, we employed thermodynamic analysis to investigate the H₂ adsorption/desorption mechanism under practical operating conditions.