Oxygen Vacancy Engineering Research Articles

Influence of Defect Engineering in Nanocrystalline CeO2 for Therapeutics of Reactive Oxygen Species-mediated Disorders.

Intracellular oxidative stress generation is a root cause of the dysfunctioning of mitochondria that is accountable for neurodegenerative disorders. In nano-CeO2, the intrinsic redox cycle (Ce3+ ⇔ Ce4+) confers them with a distinct oxygen buffering ability. Thus, increasing the Ce3+/Ce4+ ratio by preferentially engineering oxygen vacancies is expected to boost the antioxidant characteristics in CeO2 nanocrystals (NCs) and hold promise in nanotherapeutics of neurodegenerative disorders. Here, a pristine, economic, and scalable synthesis route with rapid nucleation-growth to yield monodispersed CeO2 NCs of 4 nm has been employed. The NCs demonstrated sustained colloidal stability (zeta potential ~ -30.3±7.2 mV). The survival rate (~96.1% for 0.1 mg/mL) of healthy L929 cells and cell apoptosis induced on the SH-SY5Y cells (~ 30.2% for 0.1 mg/mL) indicate nano-CeO2s' prospects in nanomedicine. The formulated sustainable synthesis strategy for the enrichment of defects in these NCs is anticipated to pave the way for nanocrystal-based-treatments in smart healthcare.Clinical Relevance-This investigation signifies the oxygen vacancy-dependent therapeutic efficacy of CeO2 NCs by ensuring ~96.1% survival rate of L929 cells while demonstrating cell apoptosis on SH-SY5Y cells (~ 30.2%) to establish newer insights on treatment of neurodegenerative disorders.

Unraveling a trade-off between positive effect and poisoning mechanism of soot over low-dose PtCu/CeO2 for simultaneously photothermocatalytic removal of VOCs and soot

It is challenging for simultaneous removal of VOCs and soot as soot would aggravate coke formation, and the lack of a deep understanding of pollutant effect on catalyst textural properties seriously limit its application. Herein, efficiently photothermocatalytic simultaneous removal of VOCs and soot was achieved by optimizing coke resistance and Pt utilization of PtCu/CeO2 through alloy modification and oxygen vacancy engineering. The findings of our combined experimental and computational study on catalytic process unravel a trade-off between positive effect and poisoning mechanism of soot, as follow: the unique photothermal properties and enhanced VOCs adsorption of soot accelerate VOCs degradation, while partially degraded soot passivate surface-active site of PtCu/CeO2 and weaken OH/O2 adsorption, thus suppressing VOCs mineralization. These new insights into the interfacial mechanism will provide a promising strategy to catalytic performance optimization and practical application.

Oxygen vacancy engineering of mesoporous Bi-Fe2O3@NC multi-channel microspheres for remarkable oxygen reduction and aqueous/flexible Zn-air batteries

Designing multi-channel mesoporous structure and introducing oxygen vacancies to synergistically enhance oxygen reduction reaction (ORR) activity is crucial for the practical application of zinc-air batteries (ZABs) in the field of energy storage and conversion. Herein, a novel multi-channel mesoporous Bi-Fe2O3 microsphere with abundant oxygen vacancies supported on nitrogen-doped carbon (denoted as Bi-Fe2O3@NC) is constructed and the designated catalyst demonstrates a higher half-wave potential (0.88 V), large limiting current density (5.8 mA cm−2@0.4 V), and superior stability. Besides, the aqueous ZAB utilizing Bi-Fe2O3@NC cathode achieves a high power density of 198.6 mW cm−2 and maintains exceptional stability for 459 h at 5 mA cm−2, superior to most previously reported catalysts. Furthermore, a solid-state ZAB assembled with Bi-Fe2O3@NC shows a power density of 55.9 mW cm−2, highlighting its potential for flexible ZAB applications. The prominent ORR performance of Bi-Fe2O3@NC can be ascribed to its unique multi-channel mesoporous structure and abundant oxygen vacancies, which increase the exposure of active sites and facilitate efficient electron/mass transport. This work provides valuable insights for the rational design of advanced ORR catalysts for the practical requirements of aqueous/flexible ZABs in energy storage and conversion.

Oxygen vacancy engineering of TiO2 nanosheets for enhanced photothermal therapy against cervical cancer in the second near-infrared window

Cervical cancer is the most common and deadly female cancer on the worldwide scale. Considering that the conventional surgery treatment and chemotherapy would cause certain side effects, photothermal therapy (PTT) possesses desired therapeutic efficiency and insignificant side effects against cervical cancer. However, the lack of efficient and safe photothermal agents that operate in the second near-infrared (NIR-II) window is a main obstacle hindering the clinical transformation of PTT. Titanium dioxide (TiO2)-based nanomaterials are commonly applied in the biomedicine field, but the weak absorption and low photothermal conversion efficiency (PCE) of TiO2 in the NIR region limit their applications in PTT. Herein, we report the oxygen vacancy engineering that is a robust strategy to regulate the electronic structures of TiO2 for photothermal conversion properties optimizing. The obtained oxygen vacancy-doped TiO2−x nanosheets exhibit strong NIR-II absorption and high PCE owing to their decreased bandgap. Specifically, the PCE of TiO2−x nanosheets is determined to be 69.5 % in the efficient NIR-II window, which is much higher than that of widely reported PTT agents. Complete tumor recession without recurrence or pulmonary metastasis is realized by enhanced NIR-II PTT via TiO2−x nanosheets at an ultralow and safe laser exposure (0.6 W/cm2). Our findings suggest that oxygen vacancy engineering of nanomaterials could regulate their photothermal conversion performances, promoting the further application of TiO2-based nanomaterials in the biomedical.

Cover Feature: Boosting the Electrochemical Performance of Lithium‐Rich Cathodes by Oxygen Vacancy Engineering (Batteries & Supercaps 7/2023)

The Cover Feature shows the Li-rich layered oxide, as promising cathode materials for powering electric vehicle (EVs) applications due to their high energy density. Post-annealing strategy is developed to pre-introduce oxygen vacancies (OVs) into Li1.2Mn0.457Ni0.229Co0.114O2 cathode to modify the local Mn coordination environments, enhance structural stability, and suppress oxygen release. The presence of oxygen vacancies through thermal expansion diminishes the phase transitions in cathode materials during the heating process. More information can be found in the Research Article by H. Gao, G. Wang and co-workers.

Facilitating Reconstruction of the Heterointerface Electronic Structure by the Enriched Oxygen Vacancy for the Oxygen Evolution Reaction

Exploring high-performance non-precious metal-based electrocatalysts for the sluggish oxygen evolution reaction (OER) process is fundamentally significant for the development of multifarious renewable energy conversion and storage systems. Oxygen vacancy (Vo) engineering is an effective leverage to boost the intrinsic activity of OER, but the underlying catalytic mechanism remains anfractuous. Herein, we realize the construction of oxygen vacancy-enriched porous NiO/ln2O3 nanofibers (designated as Vo-NiO/ln2O3@NFs hereafter) via a facile fabrication strategy for efficient oxygen evolution electrocatalysis. Theoretical calculations and experimental results uncover that, compared with the no-plasma engraving component, the presence of abundant oxygen vacancies in the Vo-NiO/ln2O3@NFs is conducive to modulating the electronic configuration of the catalyst, altering the adsorption of intermediates to reduce the OER overpotential and promote O* formation, upshifting the d band center of metal centers near the Fermi level (Ef), and also increasing the electrical conductivity and enhancing the OER reaction kinetics simultaneously. In situ Raman spectra proclaim that the oxygen vacancy can render the NiO/ln2O3 more easily reconstructible on the surface during the OER course. Therefore, the as-obtained Vo-NiO/ln2O3@NFs demonstrated distinguished OER activity, with an overpotential of only 230 mV at 10 mA cm-2 and excellent stability in alkaline medium, surmounting the majority of the previously reported representative non-noble metal-based candidates. The fundamental insights gained from this work can pave a new path for the electronic structure modulation of efficient, inexpensive OER catalysts via Vo engineering.

Ultrahigh concentration surface oxygen vacancies in ferrite foams for broadened electromagnetic absorption bandwidth

Currently, the absorbing bandwidth of the Ferrites is enormously limited at X-band and Ku-band by the poor intrinsic dielectric properties. Thus, there are few reports about the pure Ferrites’ application at 8-18 GHz. In this paper, the Ferrites composite foams (NFC) with a high surficial oxygen vacancy concentration (48.1%) were prepared by the NH4NO3 assisted solution-combustion strategy and solid phase sintering. Noteworthily, the concentration of surficial oxygen vacancy can be effectively regulated by the NH4NO3. This is facilitated to achieve balanced impedance matching. Therefore, the effective absorption bandwidth (EAB) of the NFC covered the whole X-band and Ku-band. Conduction loss and defect polarization relaxation realized by surficial oxygen vacancies were confirmed to be the key to such wide EAB for the NFC at 8-18 GHz. This work explores the important role of surficial oxygen vacancy engineering in regulating the dielectric parameters of the Ferrites, and provides a feasible strategy of surficial oxygen vacancy engineering for wide EAB electromagnetic performance at the high-frequency.

Defective core–shell NiCo2S4/MnO2 nanocomposites for high performance solid-state hybrid supercapacitors

The roles of oxygen vacancies to enhance the electrochemical performance were not clearly explained in comprehensive research. Herein, the vertically oriented NiCo2S4/MnO2 core–shell nanocomposites are in situ grown on the nickel foam (NF) surface and activated by oxygen vacancy engineering via a chemical reduction method. The scanning electron microscope (SEM) and transmission electron microscope (TEM) results show the shell-MnO2 is well coated on the core-NiCo2S4. The hierarchical core–shell nanostructures synergistically increase conductivity and provide rich faradaic redox chemical reactions. Moreover, the density functional theory (DFT) calculations further indicate that the electronic properties and structure properties in NiCo2S4/MnO2 electrode of reduction for 60 min (NiCo2S4/MnO2-60) are effectively adjusted by introducing oxygen vacancies. Impressively, the NiCo2S4/MnO2-60 electrode delivers substantially appreciable areal capacity of 2.13 mAh·cm−2 couple with superior rate capability. The as-prepared high-performance electrode material can assemble into solid-state hybrid supercapacitor. The fabricated NiCo2S4/MnO2-60//AC device exhibits an exceptional energy density of 43.16 Wh·kg−1 at a power density of 384.21 W·kg−1 and satisfactory cyclic stability of 92.1 % at current density of 10 mA·cm−2 after 10,000 cycles. In general, the work demonstrates the significance of NiCo2S4/MnO2-60 as a highly redox active electrode material for future practical application in supercapacitors.

Electrocatalytic conversion of methane to ethanol by ultrathin WO3 nanosheets: Oxygen vacancy engineering

Electrocatalytic conversion of CH4 into valuable liquid products is an attractive strategy for utilization of natural gas, however, it was still constrained by low product yields. Herein, ultrathin WO3 nanosheets with adequate oxygen vacancies (Ov) as robust electrocatalysts for highly efficient CH4 conversion to ethanol were synthesized. Using the optimized sample, the ultrahigh ethanol yield and selectivity of 125,090 μmol gcat−1 h−1 and 99.4% are achieved within 8 h at low potential of 1.2 V vs. RHE, both of which outperform the previous reports as we know. The corresponding ethanol Faradic efficiencies is 50.7%. In-situ Raman spectra and density functional theory calculation reveal that Ov effectively enable CH activation and CC coupling, and eventually promotes the electrocatalytic activity and ethanol selectivity for CH4 conversion. This work provides a constructive avenue for designing electrocatalysts with both high activity and selectivity to realize CH4 conversion.

Core-shell structure strategy and oxygen vacancy engineering of 0.1LaMnO3@0.9(Ba0.5Sr0.5)TiO3 ceramics towards tuning electrical properties

In recent years, core-shell structures have attracted much attention for their potential in tuning the functional properties of materials and have become an effective method for preparing high-performance materials. In this work, core-shell structured 0.1LaMnO3@0.9(Ba0.5Sr0.5)TiO3 nanoparticles were fabricated by sol-gel method and dense ceramics were prepared at different sintering temperatures. The phase composition, morphology, chemical state and electrical properties were systematically investigated. Structural analysis confirmed the formation of 0.1LaMnO3@0.9(Ba0.5Sr0.5)TiO3 core-shell nanostructures. The results show that the prepared samples exhibit typical negative temperature coefficient characteristics in the range of 50–1000 °C, which is derived from the effect of carrier pairs and oxygen vacancies on the electrical properties. This study provides new insights from structure to material into guiding the development and design of advanced thermistor materials for temperature sensing applications.

Engineering oxygen vacancies of 2D WO3 for visible-light-driven benzene hydroxylation with dioxygen

Solar-driven benzene oxidation with dioxygen (O2) provides a green and sustainable alternative for phenol production, but the construction of heterogeneous photocatalysts remains a huge challenge for efficient conversion under visible light irradiation and ambient conditions. Herein, we reported a facile microwave assisted strategy for the defect engineering of two-dimensional (2D) tungsten oxide while well maintaining the original crystalline architecture. Abundant oxygen vacancies were constructed on the 2D tungsten oxide, which remarkably promoted photochemical (light harvesting, charge separation and transfer) and O2 activation behaviors, this promotion effect was further strengthened by the hybridization with Pt species with the formation of Schottky junction. The champion catalyst enabled a high phenol yield of 11.3% with a selectivity of 91% in the visible-light-driven benzene hydroxylation with atmospheric O2 at room temperature. The catalyst can be facilely recovered and reused with stable activity. The oxygen vacancies and Pt co-catalyst were demonstrated to play vital roles in the photocatalytic formation of the reactive oxygen species (hydroxyl radials, ·OH) for effective oxidation.

3 nm-Wide WO3–x Nanorods with Abundant Oxygen Vacancies as Substrates for High-Sensitivity SERS Detection

Oxygen vacancy (Vo) engineering is a powerful tool to improve semiconductor metal oxide-based surface-enhanced Raman scattering (SERS) activity due to the enriched surface states of substrates. However, the current energy-consuming high-temperature hydrogen reduction methods of introducing Vo and the poor sensitivity impede practical applications of semiconductor SERS. In this work, a facile solvothermal method was developed to prepare ultrafine WO3–x nanorods (∼3 nm width) for high-performance SERS substrates. The lowest detection limit of the rhodamine 6G (R6G) molecule on the Vo substrate can be as low as 10–10 mol/L and exceeds that of unmodified WO3 by more than two orders of magnitude. Experimental and calculated results suggest that the Vo-induced localized surface plasmon resonance (LSPR), diverse vibronic coupling, and enhanced charge transfer synergistically account for this outstanding activity. These findings can provide insights into the rational design of oxygen vacancy-tailored semiconductor SERS substrates.

Engineering Oxygen Vacancies in IrOx Clusters Supported on Metal–Organic Framework Derived Porous CeO2 for Enhanced Oxygen Evolution in Acidic Media

Developing highly active and stable electrocatalysts for the oxygen evolution reaction (OER) in acidic media for proton exchange membrane water electrolysis is urgent but still challenging. Herein, porous CeO2-supported IrOx clusters with different oxygen vacancy (Ov) concentrations are synthesized by the aid of N-rich and N-free isostructural Ce-based metal–organic frameworks (Ce-MOFs) as templates. Ov concentration in the derived IrOx clusters is effectively regulated by the presence of heteroatoms in MOFs. The optimized IrOx/CeO2 catalyst with high Ov (hov-IrOx/CeO2) exhibits a low overpotential of 251 mV at 10 mA cm–2, a higher turnover frequency (TOF) of 5400 h–1 and outstanding durability for at least 98 h of catalysis in 0.1 M HClO4, outperforming other analogues. Density functional theory calculations also show that the rich Ov in IrOx can weaken the binding energy between Ir and *O intermediates, which decreases the energy barriers for forming *OOH from *O in the rate-determining step. Additionally, the suppressed over-oxidation of Ir species as well as the corrosion resistance of the CeO2 support also contribute to the high stability.

Room temperature triethylamine gas sensor with excellent performances based on novel porous CuO foam via a simple and facile route

Monitoring of explosive and toxic triethylamine (TEA) is essential for environmental safety and human health. However, high sensitivity detection of TEA remains a huge challenge at low temperature or even room temperature. Here, we developed a CuO porous foam-based gas sensor for TEA detection at room temperature by defect engineering of oxygen vacancies. The CuO porous foam with rich surface oxygen vacancies have been synthesized through a sol-gel autocombustion method, and the formation mechanism of porous foam structure and rich oxygen vacancies of CuO have been investigated by various characterization methods. Moreover, the fabricated CuO foam gas sensor reveals the high response of 140.0 for 50 ppm TEA, a low detection limit of 0.5 ppm, excellent selectivity, good stability and repeatability at room temperature, which are ascribed to porous structure and rich surface oxygen vacancies of CuO foam. Importantly, the surface redox reaction model and density function theoretical calculation have been applied to deeply explore the sensing mechanism. This work can not only realize the ultra-sensitive sensing of TEA at room temperature, but also provide a novel strategy for the design of other ideal performance sensors at low operating temperatures.

Engineering oxygen vacancy to accelerate proton conduction in Y-doped BaZrO3

Proton conducting oxides have drawn great interest as electrolytes for proton-conducting reversible solid oxide cells (P-RSOCs), but suffered from the inferior ionic conductivity. To accelerate proton conduction, oxygen vacancy engineering via calcium-doping is proposed and validated, which generates more oxygen vacancies to increase proton concentration and importantly tailors the position of oxygen vacancy to accelerate proton diffusion. TG and EIS results show that calcium-doped BaZr0.8Y0.2O3-δ (BZY2), BaZr0.8Ca0.1Y0.2O3-δ (BZCa1Y2), owns higher proton concentration, and demonstrates ionic conductivity of 0.008 S cm−2 at 700 °C, 2.7 times higher than BZY2. The lower activation energy of conductivity in BZCa1Y2 confirms the faster proton conduction behavior. DFT calculation concludes that oxygen vacancies prefer to cluster with Ca site and proton diffusion barrier is decreased most when vacancy is tailored to generate nearing Ca. When considering the concentration of proton and oxygen vacancy, proton diffusion coefficient obtained from Ab-initio Molecular Dynamics simulation is 1.1×10−5 cm2s−1 for BZCa1Y2 in 200 °C, larger than BZY2 (9.0×10−6 cm2s−1) and verifying the accelerated proton diffusion due to the tailored oxygen vacancy. The oxygen vacancy engineering provides a further understanding of proton diffusion in proton conducting oxides and a new promising opportunity to improve conductivity.

Boosting the Electrochemical Performance of Lithium‐Rich Cathodes by Oxygen Vacancy Engineering

AbstractThe challenges of voltage decay and irreversible oxygen release for lithium‐rich layered oxide cathode materials have hindered their commercial application despite their high energy density and low cost. Herein, a facile post‐annealing strategy is developed to pre‐introduce oxygen vacancies (OVs) into Li1.2Mn0.457Ni0.229Co0.114O2 cathode materials. The induced OVs modify the local Mn coordination environments, enhance structural stability, and suppress oxygen release. The modified cathode exhibits a discharge capacity of 224.1 mAh g−1 at 0.1 C after 100 cycles with 97.7 % capacity retention. Even at 2 C, excellent capacity retention of 93.3 % after 300 cycles can be achieved. In situ and ex situ X‐ray diffraction are used to elucidate the reaction mechanisms and crystal structure during cycling tests. Ex situ X‐ray photoelectron spectroscopy confirmed the suppressed oxygen release, enhanced oxygen vacancies and reduced cathode‐electrolyte interfacial layer after cycling for the post‐annealed cathode. Our results show that the presence of oxygen vacancies through thermal expansion diminishes the phase transitions in cathode materials during the heating process. These findings contribute to developing next‐generation Li‐ion batteries (LIBs) by oxygen vacancy engineering for new cathode materials with improved electrochemical performances.

Nanosecond Memristor Based on Oxygen Vacancy Engineering in SrTiO3 Single Crystal

AbstractMemristors are of great significance for the construction of memory devices and neuromorphological computing, which need a fast response time for ultrahigh data storage, ultrafast information processing, and efficient neuromorphic computing. Currently, memristors based on perovskite oxide materials generally have a long response time. In this paper, the electroforming‐free memristive behavior based on Ar+ irradiating induced oxygen vacancy modulation in SrTiO3 (STO) has been investigated. The Ag/STO/(Ta/Pt) device shows a stable bipolar resistive switching (RS) characteristic and can realize ultrafast multi‐resistance switching behavior. More importantly, its conductance can be continuously controlled with short pulse on the nanosecond scale to simulate potentiation and depression of synapse, promising potential application in ultra‐fast biological synapse and high‐efficiency training of neural networks. More importantly, the defect engineering strategy used in this work provides more freedom for the design and optimization of versatile memristor devices.

Tuning resistive switching properties of WO3− x -memristors by oxygen vacancy engineering for neuromorphic and memory storage applications

High density memory storage capacity, in-memory computation and neuromorphic computing utilizing memristors are expected to solve the limitation of von-Neumann computing architecture. Controlling oxygen vacancy (V O) defects in metal oxide thin film based memristors holds the potential of designing resistive switching (RS) properties for memory storage and neuromorphic applications. Herein, we report on RS characteristics of complementary metal–oxide–semiconductor compatible WO3−x based memristors modulated by precisely controlled oxygen non-stoichiometry. Switchability of the resistance states has been found to depend strongly on the V Os concentration in the WO3−x layer. Depending on x, the memristors exhibited forming-free bipolar, forming-required bipolar, and non-formable characteristics. Devices with moderate V Os concentration (∼5.8 × 1020 cm−3) exhibited a large R off/R on ratio of ∼6500, and reset voltage-controlled multi-level resistance states. A forming-free, stable multi-level RS has been realized for a memristor possessing V Os concentration of ∼6.2 × 1020 cm−3. WO3−x -based memristors with higher V Os concentrations (∼8.9 × 1020 cm−3–1 × 1021 cm−3) exhibited lower initial resistance, low R off/R on ratios (∼15–63) and forming-free synaptic functions with reasonable conduction modulation linearity. Investigation of the conduction mechanism suggests that tailoring V Os concentration modifies the formation and dimension of the conducting filaments and the Schottky barrier height at the WO3−x /Pt interface, which paves the way for designing WO3−x -based memristors for memory storage and neuromorphic applications.

Enhance the stability of oxygen vacancies in SrTiO3 via metallic Ag modification for efficient and durable photocatalytic NO abatement

Oxygen vacancy engineering is an appealing strategy in the direction of photocatalytic pollutant purification. Unfortunately, the short lifetime of oxygen vacancies significantly limits photocatalytic efficiencies and their application. Herein, we report that such a scenario can be resolved via plasmonic silver metal modification SrTiO3 containing oxygen vacancies, which can achieve a high NO removal rate of 70.0% and long stability. This outstanding photocatalytic activity can be attributed to the increased optical response range and carrier separation by metallic Ag with the unique character of localized surface plasmonic resonance (LSPR) effect. Moreover, the intrinsic mechanism of how the plasmonic metal could enhance the stability of oxygen vacancies is proposed. The plasmon-driven hot carriers inject SrTiO3 support that promotes the regeneration of oxygen vacancies around the interface, meanwhile, the introduction of Ag nanoparticles prevents the oxygen vacancies from being filled by the reactant. This work elucidates the unique role of plasmonic metal in photocatalysis, providing an innovative idea for improving catalytic stability.

Unraveling the Influence of Oxygen Vacancy Concentration on Electrocatalytic CO2 Reduction to Formate over Indium Oxide Catalysts

Rational engineering of oxygen vacancies in a metal oxide-based catalyst represents an effective strategy to regulate catalytic performances by influencing both their electrochemical active surface areas and the microelectronic structure. However, the precise control and modulation of the concentration and uniformity of oxygen vacancies on the catalyst surface still remains inadequately explored and poorly elucidated. Herein, we develop a facile and effective method to prepare a series of In2O3 nanorods with varying oxygen vacancy concentrations for efficient electrolytic CO2 reduction to formate. Experimental results and theoretical calculations reveal that the abundant oxygen vacancies in the In2O3 catalyst significantly improve CO2 activation and promote the production of *HCOO intermediates, achieving a maximum formate Faradaic efficiency of 91.2% at −1.27 V vs a reversible hydrogen electrode (RHE) with high partial current density and, meanwhile, superior stability. The underlying relationship between the oxygen vacancy concentration and CO2 reduction reaction (CO2RR) performance was further established. This work offers a feasible strategy to finely tune the oxygen vacancy concentration in p-block metal oxide-based catalysts for highly efficient electrolytic CO2RR.