Abstract
Room temperature oxygen hydrogenation below graphene flakes supported by Ir(111) is investigated through a combination of X-ray photoelectron spectroscopy, scanning tunneling microscopy, and density functional theory calculations using an evolutionary search algorithm. We demonstrate how the graphene cover and its doping level can be used to trap and characterize dense mixed O–OH–H2O phases that otherwise would not exist. Our study of these graphene-stabilized phases and their response to oxygen or hydrogen exposure reveals that additional oxygen can be dissolved into them at room temperature creating mixed O–OH–H2O phases with an increased areal coverage underneath graphene. In contrast, additional hydrogen exposure converts the mixed O–OH–H2O phases back to pure OH–H2O with a reduced areal coverage underneath graphene.
Highlights
One promising application of the rich variety of new 2D materials is as model systems for studying catalysis
The dense OH−H2O phase is not observed on bare Ir(111), as its formation requires going through the dilute OH−H2O phases that desorbs without the confining cover of the Gr
We have demonstrated that the dense OH−H2O phase facilitates oxygen intercalation under Gr already at room temperature and by using the Gr doping level as an additional probe we showed that O atoms are dissolved into the OH−H2O phase making it less dense and increasing its areal coverage
Summary
One promising application of the rich variety of new 2D materials is as model systems for studying catalysis. We demonstrate how the Gr doping level together with C 1s reference values for intercalated structures[19] give a novel tool to follow undercover reactions in situ Using this new tool we follow how the dense OH−H2O structure increases its areal cover underneath Gr once O atoms are dissolved into it and subsequently reduce its areal coverage upon converting the Density functional theory calculations were performed using an evolutionary search algorithm[29,30] to determine the structure and stability for OH−H2O mixed phases intercalated under an idealized (4 × 4) graphene covered (2 3 × 2 3 ) Ir(111) surface unit cell. With the used sign convention, a positive CLS corresponds to a shift to higher binding energies in the experiment
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