How to Characterize (Oxygen/Nitrogen) Defects/Vacancies at Transition Metal Oxide?

I. XPS and XRD

1. Refrences

• Engineering Interface and Oxygen Vacancies of Ni_xCo_1–xSe₂ to Boost Oxygen Catalysis for Flexible Zn–Air Batteries ACS Appl. Mater. Interfaces 2019, 11, 31, 27964–27972
• Unraveling the Influence of Oxygen Vacancy Concentration on Electrocatalytic CO₂ Reduction to Formate over Indium Oxide Catalysts ACS Catal. 2023, 13, 6, 4021–4029

2. Typical Reasons for the Formation of OXygen Vacancies

The formation of V_O″ may be caused by the following factors: (i) the lattice O was oxidized to O₂ during polarization and (ii) Se on the surface may be oxidized to Se element and peeled off, thus leading to oxygen vacancies.^{[ACS Appl. Mater. Interfaces 2019, 11, 31, 27964–27972]}

3. XPS O1s Deconvolution

Ref ^{[ACS Appl. Mater. Interfaces 2019, 11, 31, 27964–27972]}

• the O1 area at 530.2 eV corresponds to metal–O bond.
• The O2 at 531.8 eV corresponds to V_O″.
• The O3 (532.9 eV) is associated with hydroxy species or adsorbed water molecules

Ref ^{[ACS Catal. 2023, 13, 6, 4021–4029]}

The O 1s XPS spectra of the three In₂O₃ samples were deconvoluted into three peaks, corresponding to lattice oxygen (In–O, ∼529.7 eV), oxygen vacancies (∼531.4 eV), and chemisorbed oxygen (∼532.5 eV), respectively.

Ref [https://doi.org/10.1016/j.apcatb.2023.122775]

BiVO₄ has lattice oxygen (O_L) at 529.7 eV and an oxygen vacancy (O_V) at 531.7 eV [30], [31]. The ESR results also proved that there were oxygen vacancies on BiVO₄, B-Sm4 and α-Fe₂O₃ (Fig. S5). This is an inherent defect in the materials [14]. With the modification of the catalyst, the incorporation of metal Sm slightly decreased the O_L, indicating that metal Sm interacted with O. The oxygen vacancy of B-Sm4 became 530.8 eV and that of B-Sm-F became 531.1 eV. The decrease in the O_V binding energy indicates that the electrons around the O_V are enriched. This may be due to the electron transfer around Bi, resulting in the loosening and fracture of the chemical bond between Bi and O and the subsequent generation of oxygen vacancies.

4. Electron paramagnetic resonance (EPR) or electron spin resonance (ESR) spectroscopy

Mechanism: the fact that a single electron can be captured or trapped by surface oxygen vacancies in catalysts.

EPR can not only probe the defects directly with high sensitivity but also determine the type of defects by a g factor value.^{[J. Phys. Chem. C 2019, 123, 26, 16268–16280]}

Operation:

Operation

Electron paramagnetic resonance (EPR) measurements were run on a Bruker EPR A300 spectrometer at 77 K

ACS Catal. 2022, 12, 15, 9437–9445

a

ESR spectra were measured at 300 K using an ESR spectrometer (JEOL JES-FA200) at 9.08 GHz

ACS Catal. 2020, 10, 2, 1077–1085

Low temperature electron paramagnetic resonance (EPR) of solid sample was taken on Bruker-A300-10/12 spectrometer and measured at 77 K. In addition, the EPR signals of radicals were also examined on Bruker-A300-10/12 spectrometer at room temperature

ACS Catal. 2021, 11, 17, 11256–11265

no signal was detected for the In₂O₃ prepared in the air, while significant peaks located at g = 2.001 were observed for P-In₂O₃ and R-In₂O₃, indicating a much higher oxygen vacancy concentration in the In₂O₃ sample prepared in an NH₃ and a H₂ atmosphere

ACS Catal. 2023, 13, 6, 4021–4029