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Interaction of Atomic Hydrogen with the Cu2O(100) and (111) Surfaces

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journal contribution
posted on 28.08.2019, 15:42 by Heloise Tissot, Chunlei Wang, Joakim Halldin Stenlid, Mohammad Panahi, Sarp Kaya, Markus Soldemo, Milad Ghadami Yazdi, Tore Brinck, Jonas Weissenrieder
Reduction of Cu2O by hydrogen is a common preparation step for heterogeneous catalysts; however, a detailed understanding of the atomic reaction pathways is still lacking. Here, we investigate the interaction of atomic hydrogen with the Cu2O­(100):(3,0;1,1) and Cu2O­(111):(√3 × √3)R30° surfaces using scanning tunneling microscopy (STM), low-energy electron diffraction, temperature-programmed desorption (TPD), and X-ray photoelectron spectroscopy (XPS). The experimental results are compared to density functional theory simulations. At 300 K, we identify the most favorable adsorption site on the Cu2O­(100) surface: hydrogen atoms bind to an oxygen site located at the base of the atomic rows intrinsic to the (3,0;1,1) surface. The resulting hydroxyl group subsequently migrates to a nearby Cu trimer site. TPD analysis identifies H2 as the principal desorption product. These observations imply that H2 is formed through a disproportionation reaction of surface hydroxyl groups. The interaction of H with the (111) surface is more complex, including coordination to both Cu+ and OCUS sites. STM and XPS analyses reveal the formation of metallic copper clusters on the Cu2O surfaces after cycles of hydrogen exposure and annealing. The interaction of the Cu clusters with the substrate is notably different for the two surface terminations studied: after annealing, the Cu clusters coalesce on the (100) termination, and the (3,0;1,1) reconstruction is partially recovered. Clusters formed on the (111) surface are less prone to coalescence, and the (√3 × √3)R30° reconstruction was not recovered by heat treatment, indicating a weaker Cu cluster to support interaction on the (100) surface.