Exploring hydrogen binding and activation on transition metal-modified circumcoronene

Abstract

Graphene-based materials modified with transition metals, and their potential utilization as hydrogen storage devices, are extensively studied in the last decades. Despite this widespread interest, a comprehensive understanding of the intricate interplay between graphene-based transition metal systems and H₂ molecules remains incomplete. Beyond fundamental H₂ adsorption, the activation of H₂ molecule, crucial for catalytic reactions and hydrogenation processes, may occur on the transition metal center. In this study, binding modes of H₂ molecules on the circumcoronene (CC) decorated with Cr or Fe atoms are investigated using the DFT methods. Side-on (η²-dihydrogen bond), end-on and dissociation modes of H₂ binding are explored for high (HS) and low (LS) spin states. Spin state energetics, reaction energies, QTAIM and DOS analysis are considered. Our findings revealed that CC decorated with Cr (CC-Cr) emerges as a promising material for H₂ storage, with the capacity to store up to three H₂ molecules on a single Cr atom. End-on interaction in HS is preferred for the first two H₂ molecules bound to CC-Cr, while the side-on LS is favored for three H₂ molecules. In contrast, CC decorated with Fe (CC-Fe) demonstrates the capability to activate H₂ through H–H bond cleavage, a process unaffected by the presence of other H₂ molecules in the vicinity of the Fe atom, exclusively favoring the HS state. In summary, our study sheds light on the intriguing binding and activation properties of H₂ molecules on graphene-based transition metal systems, offering valuable insights into their potential applications in hydrogen storage and catalysis.

Graphical abstract