Predominance of Subsurface and Bulk Oxygen Vacancies in Reduced Manganese Oxide

Abstract

Oxygen vacancies (V o s) play a vital role in the physical and chemical properties of oxide materials and their applications. Because V o s are first produced on oxide surfaces, it has been often recognized that they are richer at the top surface than at the subsurface or bulk region. Here the depth distribution of V o s in reduced manganese oxide (MnO x ) films has been studied by a combination of ion-sputtering treatment and variable-angle Xray photoelectron spectroscopy measurement. The density of V o s on the top surface is determined to be ∼8% lower than that in the subsurface region after reduction treatment of the oxide in CO at 573 K. Density functional theory calculations show that lattice oxygen atoms in the bulk tend to migrate and fill into the V o s on the top surface with a barrier of 0.94 eV at most. The stability of V o s in the bulk is higher than that on the surface via a reduced Mn 3 O 4 skeleton, which can be reflected by the energy of oxygen filling at the V o .

Defect Engineering of Ceria Nanocrystals for Enhanced Catalysis via a High-Entropy Oxide Strategy

“…With enhanced bond covalency and maximized active sites, the CuCoFeNiMn-CeO 2 sample exhibits optimal CO oxidation capabilities. These atomistic insights into the surface and bulk structures of ceria-based HEO nanocrystals have important implications for oxygen defect engineering in reducible metal oxides . For example, the ability to control the surface and bulk oxygen defects of nanoscale HEOs is important in the exploration of new topological materials, where the interior electronic and magnetic properties are completely different from those on the surface or at the oxide–oxide interface .…”

“…These atomistic insights into the surface and bulk structures of ceriabased HEO nanocrystals have important implications for oxygen defect engineering in reducible metal oxides. 63 For example, the ability to control the surface and bulk oxygen defects of nanoscale HEOs is important in the exploration of new topological materials, where the interior electronic and magnetic properties are completely different from those on the surface or at the oxide−oxide interface. 64 More work is anticipated to unravel the metal−oxygen covalency in mixed and entropy-stabilized metal oxides, as the atomic-scale structural heterogeneities may benefit lattice oxygen activation for catalytic and sensing applications.…”

A nonmetallic plasmonic catalyst for photothermal CO2 flow conversion with high activity, selectivity and durability

“…In such systems, noble-metal nanoparticles with an localized surface plasmon resonance (LSPR) effect can enhance light utilization and generate hot carriers for chemical reactions 10 , 13 . Meanwhile, oxide components provide oxygen vacancies (V o ) to facilitate CO 2 adsorption and activation 16 , 17 . For example, Au/TiO 2 is one typical photocatalyst with LSPR effect 18 – 20 .…”

Scanning Tunneling Microscopy of Mno X Ultrathin Films on Au(111)

“…A variety of stoichiometries and structures exist for MnO x (1 < x < 2), among which Mn 3 O 4 (hausmannite, with a spinel structure) is of particular research interest because of the mixed valence states of Mn (3+ and 2+) and the possibility of a variety of surface terminations. Mn 3 O 4 growth has been studied on a range of crystalline substrates, each with a varying degree of influence on the terminations and atomic structures of Mn 3 O 4 via the mechanisms of epitaxy and associated strain, e.g., SrTiO 3 (001) [7][8][9], SrTiO 3 (111) [9,10], Si(001) [11,12], Ag(001) [13][14][15], Pd(001) [16], Cu(111) [14,17,18], and Au(111) [14,[19][20][21]. The atomic and crystalline structures of the Mn 3 O 4 films were investigated using X-ray diffraction (XRD) [7,8,10,12,21], reflection high energy electron diffraction (RHEED) [8], transmission electron microscopy (TEM) [12], atomic force microscopy (AFM) [7,10], scanning tunneling microscopy (STM) [15,17,19,20], scanning transmission electron microscopy (STEM) [17], and low-energy electron diffraction (LEED) [13][14][15][17][18][19].…”