Exciting H₂ Molecules for Graphene Functionalization

Abstract

Hydrogen functionalization of graphene by exposure to vibrationally excited H molecules is investigated by combined scanning tunneling microscopy, high-resolution electron energy loss spectroscopy, X-ray photoelectron spectroscopy measurements, and density functional theory calculations. The measurements reveal that vibrationally excited H molecules dissociatively adsorb on graphene on Ir(111) resulting in nanopatterned hydrogen functionalization structures. Calculations demonstrate that the presence of the Ir surface below the graphene lowers the H dissociative adsorption barrier and allows for the adsorption reaction at energies well below the dissociation threshold of the H-H bond. The first reacting H molecule must contain considerable vibrational energy to overcome the dissociative adsorption barrier. However, this initial adsorption further activates the surface resulting in reduced barriers for dissociative adsorption of subsequent H molecules. This enables functionalization by H molecules with lower vibrational energy, yielding an avalanche effect for the hydrogenation reaction. These results provide an example of a catalytically active graphene-coated surface and additionally set the stage for a re-interpretation of previous experimental work involving elevated H background gas pressures in the presence of hot filaments.

Sticking of atomic hydrogen on graphene

“…A selective functionalization of hcp areas by hot H atoms has been achieved and seen to give rise to highly ordered hydrogenated structures, including the opening of a gap in the electronic band structure (Balog et al 2010, Balog et al 2013, Jørgensen et al 2016. Graphene/Ir(111) is interesting in many respects, as it has been recently shown that the carbon sheet can "mediate" the catalytic activity of the substrate, and make dissociative adsorption of H 2 feasible when employing vibrationally excited molecules (Kyhl et al 2018). In this case, functionalization of the graphene surface occurs in a highly ordered manner and exhibits an avalanche effect where the first dissociative adsorption event decreases the barriers for subsequent dissociative adsorption.…”

Hydrogen interaction with graphene on Ir(1 1 1): a combined intercalation and functionalization study

“…We have recently shown that vibrationally excited molecular hydrogen, H # 2 , can functionalize graphene on iridium in a similar way to atomic hydrogen, despite the large energy cost (4.5 eV) required to break the H-H bond. Functionalization with H # 2 takes place because of the possibility to form highly stable graphane-like structures, formation of which reduces the barrier to substantially lower values when compared to the free-standing graphene case [30]. The procedure from [30] using a hot tungsten capillary was then repeated for the fully intercalated graphene system.…”

Functionalized Graphene-Based Materials as Innovative Adsorbents of Organic Pollutants: A Concise Overview

“…Functional moieties distributed on the graphene surface and edges facilitate sorbent-sorbate specific interactions, which depend on the pollutant structure. In this sense, discovering the nature of the forces involved is crucial for enhancing the adsorbent selectiveness and performance (Kyhl et al, 2018). The most reported interactions are π−π stacking, electrostatic, van der Waals forces and H-bonds (Xue et al, 2018;Das et al, 2017;Wang et al, 2017a).…”