Enhanced hydrogen storage performance of graphene nanoflakes doped with Cr atoms: a DFT study

The hydrogen storage performances of novel graphene nanoflakes doped with Cr atoms were systematically investigated using first-principles density functional theory. The calculated results showed that one Cr atom could be successfully doped into the graphene nanoflake with a binding energy of -4.402 eV. Different from the H₂ molecule moving away from the pristine graphene nanoflake surface, the built Cr-doped graphene nanoflake exhibited a high affinity to the H₂ molecule with a chemical adsorption energy of -0.574 eV. Moreover, the adsorptions of two to five H₂ molecules on the Cr-doped graphene nanoflake were studied as well. It was found that there were a maximum of three H₂ molecules stored on the graphene nanoflake doped with one Cr atom. Also, the further calculations showed that the numbers of the stored H₂ molecules were effectively improved to be six (or nine) when the graphene nanoflakes were doped with two (or three) Cr atoms. This research reveals that the graphene nanoflake doped with Cr atom could be a promising material to store H₂ molecules and its H₂ storage performance could be effectively enhanced through modifying the number of doped Cr atoms.