Computational Evaluation of Lithium-Functionalized Carbon Nitride (g‑C6N8) Monolayer as an Efficient Hydrogen Storage Material

Quantum chemical density functional theory calculations have been used to study the structural, electronic, and hydrogen storage properties of a monolayer that is a stable allotrope of carbon nitride (g-C6N8). It was observed that a 2 × 2 supercell can bind three, six, and eight lithium (Li) adatoms in different configurations with a binding energy much higher than the cohesive energy of Li, indicating that a distribution of Li over the monolayer can form without clustering of Li occurring. Density of states calculations suggests that adding Li atoms transforms the semiconducting (g-C6N8) monolayer into a conducting one. A significant amount of charge is transferred from Li to the monolayer that induces a partial positive charge on each Li adatom. This facilitates the polarization of the H2 molecules exposed to Li, which are then held by it through electrostatic and van der Waals interactions. Each Li can adsorb multiple H2 molecules with adsorption energies that lie within the desired range for an efficient and reversible H2 storage material with a storage capacity of 7.55 wt %.