Atomic Origin of the Autocatalytic Reduction of Monoclinic CuO in a Hydrogen Atmosphere

Abstract

Reducibility is key for the use of bulk metal oxides in chemical transformations involving redox reactions, but probing microscopic processes of oxide reduction is challenging. This is because the insulating nature of bulk oxides restricts ion and electron spectroscopic measurements of oxide surfaces. Herein, using a combination of environmental transmission electron microscopy and atomistic modeling, we report direct in situ atomic-scale observations of the surface and subsurface dynamics and show that the hydrogen-induced CuO reduction occurs through the receding motion of Cu–O/Cu bilayer steps at the surface, the formation of the partially reduced CuO superstructure by the self-ordering of O vacancies in the subsurface, and the collapse of Cu–O layers in the bulk. All these substeps can be traced back to the progressively increased concentration and activity of O vacancies in the surface and subsurface of the oxide, thereby leading to the self-accelerated oxide reduction. These results demonstrate the microscopic details that may have a broader applicability in modulating various redox processes.

Au@Cu2O Core–Shell and Au@Cu2Se Yolk–Shell Nanocrystals as Promising Photocatalysts in Photoelectrochemical Water Splitting and Photocatalytic Hydrogen Production

“…As displayed in Figure S3a, b, grains with different orientations can be identified in the Cu 2 O and Cu 2 Se shells, the boundaries of which were highlighted with dashed lines. On the other hand, the existence of vacancies can be unambiguously recognized from the alternative bright and dim contrast in the atomic-scale image Figure S3c, d presents the magnified HRTEM images at the regions marked with dash squares in Figure S3a, b.…”

“…On the other hand, the existence of vacancies can be unambiguously recognized from the alternative bright and dim contrast in the atomic-scale image. 35 Figure S3c, d presents the magnified HRTEM images at the regions marked with dash squares in Figure S3a, b. The inset intensity profiles clearly revealed the prevalence of weakened bright atoms along a selected row, suggesting that some lattice sites were vacant.…”

Revealing an Intermediate Cu–O/OH Superstructure on Cu(110)

“…Therefore, the competing action of simultaneously present oxidizing and reducing gases may lead to complex spatial-temporal dynamic changes in the surface structure and composition under the reaction conditions. This is demonstrated by recent in situ electron microscopy observations showing the oscillatory redox phase transitions induced by the interconversion between coexisting metal and oxide during hydrogen oxidation over Cu or CuO surfaces. − …”

Nematic‐type Structure of the SnO2(110) Surface at Room Temperature

“…The AC-TEM has been successfully applied to the (100) and (101) surfaces of SnO 2 , [15,18] the subsurface reconstruction of the materials with the spinel structure, [16,[20][21][22] and other transition metal oxide. [12,14,17,19,[23][24][25][26][27][28] In this work, a more stable nematic SnO 2 (110) surface, which is stabilized at room temperature, is determined by using the negative Cs imaging (NCSI) technique of AC-TEM, [29][30][31] combined with image simulations and DFT calculations. It shows that the building blocks of the (110) surface are the Sn 2 O 2 strands which have been predicted by theoretical calculations.…”

“…By the profile imaging, AC‐TEM has better performance to determine local surface structures and nanoparticles. The AC‐TEM has been successfully applied to the (100) and (101) surfaces of SnO 2 , [15,18] the subsurface reconstruction of the materials with the spinel structure, [16,20–22] and other transition metal oxide [12,14,17,19,23–28] …”