Exploration of Hydrogen Storage Exhibited by Rh-Decorated Pristine and Defective Graphenes: A First-Principles Study

We utilized density functional theory (DFT) to ascertain the storage of hydrogen in Rh-decorated pristine (PG) and defective graphenes, primarily graphitic-N (GNG) and pyridinic-N (PNG). The binding energy of a single Rh atom on PG, GNG, and PNG was found to be −1.87, −2.18, and −4.01 eV, respectively. PG exhibits a weak adsorption energy of hydrogen molecules (−0.06 eV/H₂). On the other hand, Rh-decorated pristine and defective graphenes show incredibly higher hydrogen adsorption energy. As per the latest guidelines of the U.S. Department of Energy (DOE), the Rh-decorated GNG (Rh@GNG) is found to be the best hydrogen storage material out of the three systems investigated here. The single Rh atom-decorated GNG adsorbs up to 4H₂. Uniform decoration of graphene surfaces with Rh atoms is necessary to improve hydrogen storage performance. Both sides of GNG surfaces are decorated with 8Rh atoms, which can adsorb up to 24H₂ molecules, with an average adsorption energy of −0.33 eV/H₂. The mechanism of H₂ adsorption on the host system has been explored based on DFT-evaluated deformation of charge density, partial density of states (PDOS), and non-covalent interaction (NCI) plots. For a better understanding of the adsorption process, the diffusion energy barrier of Rh metal is computed using the climbing image nudged elastic band (CI-NEB) method, and the thermal stability has been evaluated through ab initio molecular dynamics (AIMD) simulations.