Enhanced Oxide Reduction by Hydrogen at Cuprous Oxide-Copper Interfaces near Ascending Step Edges

Understanding the dynamic processes involved in the interaction of hydrogen with oxides is of fundamental importance in catalysis. This paper probes the reduction of Cu₂O-"29" surfaces by hydrogen at room temperature combining in situ ambient pressure scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) calculations. Reduction of the atomic layer thin Cu₂O film is observed to be preferentially initiated at step edges and terrace defects, where perfect Cu₂O(111) terraces are found to be stable toward hydrogenation under the same conditions. After a long induction period, regions of partially reduced Cu₂O-"29" and metallic Cu coexist before the surface is fully reduced to Cu(111). The reduction rate strongly depends on the nature of nearby Cu step edges. We propose a mechanism for the reduction of Cu₂O-"29" by hydrogen where free copper atoms from ascending metallic step edges facilitate the formation of active ensembles for H₂dissociation and transfer H to the edges of Cu₂O regions.