The role of oxygen vacancies: Triggering lattice oxygen oxidation mechanism in acidic OER

The mechanisms underlying the reaction between carbon monoxide (CO) and activated dioxygen on metal oxide substrates to produce CO2 remain poorly understood, particularly regarding the role of oxygen vacancies and the nature of the activated O2 adsorbate. In this study, we present experimental findings from infrared reflection-absorption spectroscopy on a model system of bulk monocrystalline CeO2(111). Contrary to expectations, exposing the reduced surface to dioxygen (O2) at 80 K does not yield activated oxygen species, such as superoxo or peroxo. Notably, in the presence of adsorbed CO, an unexpected low-temperature oxidation reaction occurs, consuming CO while oxidizing the CeO2 substrate. Since a direct reaction between impinging O2 and adsorbed CO is unlikely at these low temperatures, a novel mechanism is proposed. Extensive spin-polarized density functional theory (DFT) calculations reveal that oxygen vacancies play a critical role in this low-temperature CO oxidation. Initially located in the subsurface region (Vss), these vacancies migrate to the surface (Vs) via a concerted interaction with coadsorbed CO and O2, leading to O2 activation and the formation of superoxo or peroxo species. Detailed analysis identifies key reaction intermediates and quantifies their adsorption energies and activation barriers. Our findings suggest that the peroxo-mediated pathway, with its lower activation barrier, is more favorable for CO oxidation at low temperatures compared to the carbonate pathway. This study provides valuable insights into the dynamic role of subsurface oxygen vacancies in the activation of gaseous O2 and CO oxidation mechanisms on CeO2.

Smart oxygen vacancy engineering to enhance water oxidation efficiency by separating the different effects of bulk and surface vacancies

Green emission in ZnO nanostructures—Examination of the roles of oxygen and zinc vacancies

Defect engineering, such as modification of oxygen vacancy density, has been considered as an effective approach to tailor the catalytic performance on transition-metal oxide nanostructured surfaces. The role of oxygen vacancies (OV) on the surface of the as-prepared, zinnia-shaped morphology of CuO nanostructures and their marigold forms on calcination at 800 °C has been investigated through the study of model catalytic reactions of reduction of 4-nitrophenol and aerobic oxidation of benzyl alcohol. The OV on the surfaces of different morphologies of CuO have been identified and quantified through Rietveld analysis and HRTEM, EPR, and XPS studies. The structure-activity relationships between surface oxygen vacancies (OV) and catalytic performance have been systematically investigated. The enhanced catalytic performance of the cubic CuO nanostructures compared to their as-prepared forms has been attributed to the formation of surface oxygen species on the reactive and dominant (110) surface that has low oxygen vacancy formation energy. The mechanistic role of surface oxygen species in the studied reactions has been quantitatively correlated with the catalytic activity of the different morphological forms of the CuO nanostructures.

Enhancement mechanism of full-solar-spectrum catalytic activity of g-C3N4-x/Bi/Bi2O2(CO3)1-x(Br, I)x heterojunction: The roles of plasma Bi and oxygen vacancies

Roles of oxygen vacancy and ferroelectric polarization in photovoltaic effects of BiFeO3 based devices

Highly efficient Cu/CeO2-hollow nanospheres catalyst for the reverse water-gas shift reaction: Investigation on the role of oxygen vacancies through in situ UV-Raman and DRIFTS

A combined experimental and computational study of an oxygen‐deficient Li2MnO3−δ (δ≈0.071) cathode for understanding the role and effects of oxygen vacancies on phase transformation and electrochemical activity in Li‐ion batteries is presented. The oxygen‐deficient Li2MnO3−δ exhibits improved electrochemical reactivity toward Li+ ions without significant loss of structural stability. The oxidation of O during Li+ ion extraction can be suppressed by the enhanced redox reaction of Mn in this material. Furthermore, the inevitable phase transformation of Li2MnO3 can be impeded by the increased kinetic barriers to Mn migration in Li2MnO3−δ (ΔEbarrier=1.0–2.5 eV), which disfavors the formation of stable intermediate coordination geometries due to the oxygen vacancies. These findings reveal the underlying mechanism on the role of the oxygen vacancies in changing phase transformation and electrochemical activity in inactive Li2MnO3, and provide a scientific insight to the electrochemical reactivity and sustainability of Li‐rich oxide cathode materials in Li‐ion batteries.

The roles of oxygen vacancies in electrocatalytic oxygen evolution reaction

Oxygen vacancies play an important role in the performance improvement of oxide semiconductors as photoanodes for water splitting, such as TiO2, WO3, and Fe2O3. Conductivity improvement due to the presence of oxygen vacancies was reported to be the main reason for the enhanced performance. However, oxygen vacancies may also affect light absorption and charge transfer through the solid/electrolyte interface. The roles of oxygen vacancies have not been thoroughly discussed in the past. Herein, with hematite as an example, the effects of oxygen vacancies on bulk charge transport and surface catalysis are quantitatively analyzed by decoupling photon absorption, interfacial charge transfer and charge separation processes. Oxygen vacancies improve the charge separation of both pristine and Ti-doped hematite. However, opposite observations are found in the charge transfer process for pristine and Ti-doped hematite: the positive effect in pristine hematite but the negative effect in the Ti-doped one. An electrochemical technique is used to analyze the different influences on pristine and Ti-doped hematite to unravel the mechanism of the opposite observations caused by oxygen vacancies. The current study sheds lights on how oxygen vacancies affect various aspects of important factors behind PEC performance, which is helpful to the development of more efficient photoanodes in the future.

Role of oxygen vacancy in metal oxides for photocatalytic CO2 reduction

Roles of oxygen vacancies in layered double hydroxides-based catalysts for wastewater remediation: fundamentals and prospects.

Role of oxygen vacancy in dissociation of oxygen molecule on SOFC cathode: Ab initio molecular dynamics simulation

Tuning the level of oxygen vacancies in metal oxide materials is a promising approach to enhance resistive switching properties towards memory applications. To comprehensively understand the microstructure and oxygen vacancy migration mechanism of oxide materials, recent research in controlling the concentration of oxygen vacancies and the relationship between oxygen vacancy and resistive switching behavior as well as computational study have been reviewed in this work. In particular, the role of oxygen vacancies on the resistive switching properties of various metal oxides, including transition oxides, perovskite oxides and complex oxides are discussed in this review. Moreover, different types of processing methodologies of oxygen vacant oxide materials are reviewed and compared in detail. In the end, the future trends in fine tuning the level of oxygen vacancies are reviewed and discussed.

Role of oxygen vacancies in vanadium oxide and oxygen functional groups in graphene oxide for room temperature CO2 gas sensors