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

Inspired by the promise of hydrogen (H-2) 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 H-2 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 H-2 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 H-2 molecules with adsorption energies ranging between 0.15 and 0.60 eV/H-2, which results in optimal H-2 storage capacities. Finally, we employed thermodynamic analysis to investigate the H-2 adsorption/desorption mechanism under practical operating conditions. (C) 2019 Elsevier Ltd. All rights reserved.