Oxygen Vacancy Engineering Research Articles

Oxygen vacancy boosted microwave absorption in CeO2 hollow nanospheres

Oxygen vacancy engineering is one of the key strategies to modulate the electric structure and properties of metal oxides. However, the relationship between oxygen vacancies and electromagnetic wave (EMW) absorption capabilities is so far unclear. Herein, oxygen vacancy boosted microwave absorption was realized over CeO2 dual-shell hollow nanospheres (HNSs), which can be tuned by thermal conversion temperatures (Ts) of CeOHCO3 HNSs. The lattice stress decreases linearly, and the conductivity increases gradually with the elevating Ts. Our findings show that a moderate Ts favors the formation of dual-shell CeO2 HNSs with a high oxygen vacancy concentration, a large SBET, an appropriate lattice defect, and proper conductivity. The abundant oxygen vacancies endow CeO2 HNSs with massive localized electrons and dipole centers, which benefit the conductivity, conductive loss, defect/dipole polarizations. CeO2 DSHNSs formed at Ts = 400 °C bear broad bandwidth (5.44 GHz) and strong absorption (−43.28 dB), far superior to the reported CeOHCO3 single-shell HNSs, CeO2 single-shell HNSs, and most other CeO2-based composites. Overall, this work establishes a clear correlation between oxygen vacancy defects and EMW dissipation ability, offering valuable insights for designing superior EMW absorbents.

Enhanced photo-carrier transportation at semiconductor/electrolyte interface of TiO2 photoanode by oxygen vacancy engineering

The practicality of photoanodes for photoelectrochemical (PEC) water splitting was severely hampered by poor bulk photo-carrier separation and slow surface reaction kinetics. Here, we report an oxygen vacancy-enriched TiO2 photoanode modified by a highly crystalline TiO2 layer with enhanced bulk photo-carrier separation and surface reaction kinetics through stepwise gas diffusion at elevated temperatures. Experimental studies reveal that the reduction treatment introduces oxygen vacancy to TiO2, thereby increasing the charge carrier concentration and shifting the Fermi level to conduction band. The oxidation treatment affects the oxygen vacancy distribution of TiO2 surface which forms a suitable Fermi energy difference with the bulk, thus accelerating the carriers’ drift near to semiconductor/electrolyte interface. The as-obtained TiO2 photoanode exhibits an enhanced photocurrent density of 2.26 mA cm−2 at +1.23 V vs. RHE which is 2.75 times higher than that of the pristine TiO2. Hence, the present work illustrates the great potential of oxygen vacancy engineering via simple gas annealing treatment for Fermi level manipulation that can be further explored to other metal oxide semiconductors to design highly efficient oxygen vacancy enriched crystalline PEC photoelectrodes and provides novel insights into contact interfaces between semiconductors and electrolytes in PEC water splitting.

Boosting near-infrared absorption properties enabled by oxygen vacancy engineering within tungsten trioxide

Tungsten-based semiconductor nanomaterials have great potential for developing energy-saving windows as a consequence of excellent shielding performance in the near-infrared (NIR) region. The performance of such nanomaterials is profoundly influenced by the the oxygen vacancies (OVs). However, the relationship between NIR absorption properties and OVs concentration has been rarely explored. In this work, the WO3-x nanosheets capable of various OVs concentration were successfully synthesized via a simple solvothermal approach, and we have carefully investigated their optical properties. Particularly, we found that the WO3-x-Pr nanosheets showed the strongest UV and NIR absorption, with the transmittance in visible region is up to 60%. Furthermore, this material is capable of the lowest temperature gap (about 11.4 °C). This work manifests that the optical performance of the tungsten (W)-based semiconductor nanomaterials is highly depended by the OVs concentration.

A facile and high-effective oxygen defect engineering for improving electrochemical performance of lithium-rich manganese-based cathode materials

The irreversible evolution of oxygen for lithium-rich manganese-based cathode (LRMC) is the main challenge which will induce accelerated migration of transition metal ions and structural transformation, thus resulting in serious voltage attenuation and capacity decay. Herein, a facile and high-effective oxygen vacancy engineering of hydrogenation treatment is proposed for introducing oxygen vacancy on the surface of LRMC to suppress the irreversible evolution of oxygen. X-ray diffraction (XRD) Rietveld refinement, X-ray photoelectron spectroscopy and electron paramagnetic spectroscopy demonstrate the successful introduction of oxygen vacancy on the surface of LRMC. The changes of physicochemical properties of LRMC after hydrogenation treatment are investigated through systematical electrochemical performance tests and scanning electron microscopy and transmission electron microscopy. The investigative results reveal that the presence of oxygen vacancy can significantly improve the structural stability, electrical conductivity and Li+ diffusion kinetics of the LRMC materials. Especially, the optimized H500-LRMC shows excellent electrochemical performances including the enhanced cyclic stability with a capacity retention of 221.8 mAh g−1 and a capacity retention rate of 94.11% after 100 cycles. Therefore, the well-designed oxygen vacancy engineering through hydrogenation treatment is a promising strategy for the development and industrialization of the high-performance LRMC.

Oxygen vacancy engineering of photocatalytic nanomaterials for enrichment, activation, and efficient removal of nitrogen oxides with high selectivity: a review

Oxygen vacancy engineering of photocatalytic nanomaterials for enrichment, activation, and efficient removal of nitrogen oxides with high selectivity: a review

La-RuO2 nanocrystals with efficient electrocatalytic activity for overall water splitting in acidic media: Synergistic effect of La doping and oxygen vacancy

The development of high-performance and durable Ru-based electrocatalysts in proton exchange membrane (PEM) water electrolyzers for both the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) remains a huge challenge due to the severe catalyst’s corrosion and high reaction overpotential in acid media. Herein, we reported a synergistic strategy of effectively combining hetero-atom doping and oxygen vacancy in the La-doped RuO2 nanocrystals, successfully realized by a hydrothermal and followed annealing process aiming for efficiently overall water splitting. The as-obtained La-doped RuO2 nanocrystals demonstrate superior electrocatalytic performances with ultra-low overpotential of 208 mV for OER and 71 mV for HER at the current density of 10 mA/cm2 together with robust long-term stability in 0.5 M H2SO4 electrolyte, which are 222 and 15 mV lower in overpotentials than that of bare RuO2 electrocatalyst. Moreover, the La-doped RuO2 nanocrystals only require a cell voltage of 1.53 V to drive the overall water splitting reaction and exhibit a remarkable stability. Density functional theory (DFT) calculations further reveal that the synergistic effect of La doping and oxygen vacancy engineering could tune the d-band center of Ru active sites and optimize the Gibbs free energy of intermediate state, thus enhancing the activity of RuO2. Such synergistic strategy of aliovalent doping and vacancy engineering for much enhanced acid electrocatalysis may offer important referential values for exploring efficient electrocatalysts towards overall water splitting in acidic media.

Photoelectrochemical Antibacterial Platform Based on Rationally Designed Black TiO2-x Nanowires for Efficient Inactivation against Bacteria.

A hyphenated strategy for photoelectrochemical (PEC) disinfection is proposed with rationally designed black TiO2-x as a photoresponsive material. The PEC method, a fusion of electrochemistry and photocatalysis, is an innovative and effective way to improve photocatalytic performance, which imparts certain properties to the photoelectrode and greatly promotes the charge transfer, thus effectively inhibiting the recombination of carriers and greatly promoting the catalytic efficiency. The oxygen vacancy (Vo) engineering on TiO2 is conducted to obtain black TiO2-x, which shows a much larger light absorption region in the full solar spectrum than the pristine white TiO2 and presents excellent PEC sterilization performance. The bactericidal efficiency with the PEC method is 10 times higher than that with the photocatalytic method, inactivating 99% of bacteria within a short time of 30 min. In addition, the black titanium oxide nanowires (B-TiO2-x NWs) are grown on flexible carbon cloth (CC) to form a sandwich structural self-cleaning face mask. The bacteria adhering to the surface of the mask will be sterilized quickly and efficiently under the illumination of visible light. The face mask with the characteristics of superior antibacterial effect and long service lifetime will be used for epidemic prevention and reduce the second pollution.

Co9S8@MnO2 core–shell defective heterostructure for High-Voltage flexible supercapacitor and Zn-ion hybrid supercapacitor

Flexible and wearable energy storage devices have drawn increasing attention owing to the rapid development of smart and portable electronic gadgets. Herein, vertically oriented Co9S8@MnO2 core–shell heterostructure nanotube arrays are in situ grown on the carbon cloth surface and activated by oxygen vacancy engineering via a fast NaBH4 reduction method. The introduction of oxygen vacancy can effectively improve the conductivity, reaction kinetics and thus increase the capacitance performance. The as-prepared high-active electrode material can assemble into high-performance flexible supercapacitor and Zn-ion hybrid supercapacitor. The assembled flexible all-solid asymmetric supercapacitors (AAS) show a wide potential window of 2.4 V, the excellent areal capacitance of 0.8058F cm−2 at 2 mA cm−2, high energy density of 92.14 Wh kg−1 and power density of 342.86 W kg−1. Further, the assembled Zn-ion hybrid supercapacitor has a higher energy density of 198.857 Wh kg−1, which is about twice than that of AAS devices. This work provides a rational strategy for design energy storage devices with high energy density and voltage window.

A hypoxia-irrelevant Fe-doped multivalent manganese oxide sonosensitizer via a vacancy engineering strategy for enhanced sonodynamic therapy

Sonodynamic therapy (SDT), as a noninvasive treatment with preferable therapeutic depth, has attracted widespread attention. However, current sonosensitizers suffer from a low quantum yield of ultrasound (US)-triggered reactive oxygen species (ROS), and their efficacy is greatly compromised by hypoxia, a characteristic feature of most solid tumors. To address this issue, a hypoxia-irrelevant sonosensitizer, namely, Fe-doped multivalent manganese oxide nanoparticle (FDMN), was developed via an oxygen vacancy engineering strategy. The prepared FDMNs possessed sufficient oxygen vacancies (OVs) due to the doping of Fe3+ into the multivalent manganese oxide lattice, which allowed efficacious ROS generation by preventing the recombination of sono-triggered electron-hole pairs. Specifically, due to the OVs structures, oxygen molecules were adsorbed on the surface of FDMNs, bestowing nanosonosensitizers with a hypoxia-irrelevant singlet oxygen (1O2) generation ability, which has not been shown before. Furthermore, FDMNs were capable of catalyzing endogenous O2 into highly toxic 1O2 without any exogenous stimulus to realize ROS overproduction, inherited from multivalent manganese oxides, and eliminating glutathione (GSH) to amplify the oxidative stress. All these synergistic effects result in a superior therapeutic outcome even in hypoxic microenvironment. Overall, this work illustrates that the vacancy engineering strategy is a favorable method to rationally construct a hypoxia-irrelevant sonosensitizer for highly efficient and safe SDT.

Multilevel resistive switching in graphene oxide-multiferroic thin-film-based bilayer RRAM device by interfacial oxygen vacancy engineering

Multilevel resistive switching in graphene oxide-multiferroic thin-film-based bilayer RRAM device by interfacial oxygen vacancy engineering

Mechanochemically tailoring oxygen vacancies of MnO2 for efficient degradation of tetrabromobisphenol A with peroxymonosulfate

Oxygen vacancy (VO) engineering can efficiently improve the catalytic activity of metal oxides. This work developed a solvent-free mechanochemical method to tailor VO levels on the surface of commercial MnO2 under ambient conditions. After a typical ball milling treatment at 350 rpm for 20 min, the obtained VO-rich MnO2 activated peroxymonosulfate (PMS) to completely degrade tetrabromobisphenol (TBBPA) with a pseudo-first-order rate constant of 0.21 min−1, being 22 times larger than that for non-milled MnO2. 18O-labeling tests confirmed that singlet oxygen was generated from both PMS and lattice oxygen of MnO2 as dominant active species for the TBBPA degradation. It was clarified that the catalytic activity of MnO2 depends on not only VO levels, but also the local environment of VO, i.e., VO-associated cations. The Mn4+/Mn3+ redox couple is more important than Mn3+/Mn2+, and VO improves the oxygen mobility in/on MnO2 and Mn4+/Mn3+ redox reactions for the activation of PMS.

Tailored oxygen defect coupling composition engineering Co Mn2O4 spinel hollow nanofiber enables improved Bisphenol A catalytic degradation

Hollow nanofiber composed of Co 2 Mn 2 O 4 nanocrystals with modulated composition engineering and tailored oxygen-vacancy sites was constructed through electrospinning and successive thermal-treatment, rendering improved activated efficiency of peroxymonosulfate in Bisphenol A (BPA) degradation. • One dimensional Co x Mn 2 O 4 hollow nanofibers were constructed by electrospinning approach. • The precise composition engineering was introduced into specially-configurated spinel catalyst. • The resulted catalyst embraces the beneficial active interface and tailored oxygen vacancy engineering. • The activation of PMS over tailored oxygen vacancy site of spinel was demonstrated. • The resulted catalyst affords excellent catalytic bisphenol A degradation efficiency. Hollow nanofiber composed of Co 2 Mn 2 O 4 nanocrystals with modulated composition engineering and tailored oxygen-vacancy sites was constructed through electrospinning and successive thermal treatment, rendering improved activated efficiency of peroxymonosulfate (PMS) in Bisphenol A (BPA) degradation. Importantly, the similar coordination orbits of Co and Mn allow them to occupy simultaneously tetrahedral and octahedral sites of spinel configuration in a stable state even by tuning Mn/Co composition. The XPS results further reveal that tailored oxygen-vacancy sites were given by tuning composition engineering in Co x Mn 2 O 4 spinel. Impressively, the rational composition proportion could further induce the regulation of most active Co(II) and Mn(III) in spinel for promoting electron-transferring and enhancing catalytic property. The catalytic tests revealed that the CMO catalyst affords the best degradation activity of BPA (k = 0.229 min −1 , 30 mg L -1 ) by the improved activation of pmonopersulfate over the optimized oxygen vacancy of spinel, whose superiority for adsorption and activation of PMS was further elucidated by Density-Functional-Theoretical calculation.

Tuning oxygen vacancies in spinel nanosheets for binder-free oxygen cathodes with superior catalytic activity in zinc-air batteries

As a promising energy storage technology, zinc-air battery (ZAB) has attracted much attention because of its safety, cleanliness, and potential high efficiency. However, slow kinetics of the oxygen evolution and reduction reactions (OER and ORR) on air cathode significantly limit the battery performance. Herein, a facile two-step tuning strategy is investigated to convert NiCoLDH to oxygen vacancy-rich NiCo2O4 nanosheet (R–NiCo2O4-x/CC). With carefully controlled air annealing and NaBH4 treatment processes, the optimal R–NiCo2O4-x/CC exhibits enhanced OER and ORR activities compared with NiCo2O4/CC counterpart. Liquid and quasi-solid-state ZABs based on the binder-free R–NiCo2O4-x/CC electrode demonstrate power density and cycling stability that surpass the reference RuO2+Pt/C/CC catalyst with open-circuit voltage and peak power density of 1.486 and 1.39 V, and 88.6 and 38.6 mW cm−2, respectively. This study provides a new approach toward high-performance catalysts for ZABs using an oxygen vacancy engineering strategy under mild conditions.

Oxygen vacancies activated porous MnO/graphene submicron needle arrays for high-capacity lithium-ion batteries

Engineering oxygen vacancies (Ovs) in submicron transition metal oxides (TMOs) is a promising way to fabricate high-capacity anodes for lithium-ion batteries (LIBs). Herein, oxygen vacancies activated porous MnO/graphene submicron needle arrays (Ovs-MnO/G NAs) are directly grown on flexible nanoporous Cu–Mn substrate by chemical vapour deposition and hydrogen etching method, and their lithium-ion diffusion and storage mechanisms and morphology evolution are systematically investigated at submicron scale. It can be concluded that these modification strategies synergistically guarantee the fast charge transfer, effective lithium-ion diffusion and storage behaviour, and electrode structural stability. Thus, the optimal Ovs-MnO/G NAs electrode deliver a high reversible capacity of 7.7 mAh cm−2 after 100 cycles at 0.2 mA cm−2 and outstanding cycling performance of 6.12 mAh cm−2 after 500 cycles at 1.0 mA cm−2. Furthermore, the Ovs-MnO/G NAs//NCM 523 full cells also achieve high average capacities of 6.74 mAh cm−2 and cycling stability of 3.88 mAh cm−2 after 100 cycles at 0.2C, indicating its practical application value.

Oxygen vacancy engineering of novel ultrathin Bi12O17Br2 nanosheets for boosting photocatalytic N2 reduction

The conversion of N2 to NH3 is one of the most promising processes in maintaining natural life and chemical production. Photocatalytic nitrogen reduction reaction (NRR) has the advantage of clean and sustainable, which is considered to be an ideal synthesis technology. In this work, we report the successful synthesis of Bi12O17Br2 ultrathin nanosheets through simple alkali treatment and solvothermal method. The Bi12O17Br2 ultrathin nanosheets can improve the separation of carriers and the transfer of photogenerated electrons to N2 molecules, thus improving the photocatalytic efficiency. Of note, the higher Bi/Br atomic ratio in Bi12O17Br2 is beneficial to broaden the light absorption edge, and the high concentration of O atoms is easy to produce oxygen vacancies on the surface during the synthesis process of Bi12O17Br2. The abundant oxygen vacancies and high specific surface area enable N2 molecules and water to have powerful chemical adsorption and activation. In addition, the photocatalytic reduction of N2 to NH3 in pure water shows excellent and stable performance, and the average generation rate of NH3 reaches up to 620.5 μmol·L-1·h−1. This study discovers that rich oxygen vacancies and ultrathin morphology may have a significant part in the process of the photocatalytic nitrogen reduction reaction.

Engineering oxygen vacancies in metal-doped MnO2 nanospheres for boosting the low-temperature toluene oxidation

Promoting the catalytic activity by engineering oxygen vacancies is a fascinating strategy in heterogeneous catalysis. Herein, a series of metal oxide catalysts with different metal doping were prepared through a redox precipitation method to regulate oxygen vacancies in MnO2 and tested in toluene catalytic oxidation at low temperature. To accurately elaborate the structure–activity relationship of different catalysts, the prepared catalysts were systematically characterized by various techniques. Results showed that the doped metals entered the MnO2 skeleton as expected and resulted in the lattice distortion, as well as oxygen vacancies. The catalyst Cu-MnO2, which was obtained by doping Cu into MnO2, had the most oxygen vacancy contents and increased oxygen migration mobility, thus showing the best catalytic toluene oxidation activity at low temperature (T90 = 219 °C). Meanwhile, in-situ DRIFTs demonstrated the intermediates like benzene methanol, benzaldehyde, benzoic acid, maleic acid generated at different environments and revealed that the rate-controlling step probably be the deep oxidation of benzoate species. In addition, the supplement of gas phase oxygen played an important role in the complete transformation of the intermediate benzoic acid. This work open up an attractive method for acquiring metal-doped MnO2 nanospheres catalysts for toluene oxidation.

Engineering Oxygen Vacancies in Co3o4 to Boost P-D Hybridization for Hydrogeneration of Nitrogen and Oxygen

Engineering Oxygen Vacancies in Co3o4 to Boost P-D Hybridization for Hydrogeneration of Nitrogen and Oxygen

Defect engineered SnO2 nanoparticles enable strong CO2 chemisorption toward efficient electroconversion to formate.

Oxygen vacancy (Ov) engineering of SnO2 electrocatalysts plays a crucial role in realizing efficient CO2 electroreduction (CO2RR) into formate. Herein, we demonstrate the rational synthesis of highly dispersed SnO2 nanoparticle electrocatalysts with an ultrahigh Ov content of up to 25.1% by a thermally induced strategy. The high Ov content greatly improves the intrinsic conductivity and remarkably enhances the chemisorption capacity to CO2, thus boosting the catalytic activity and reaction kinetics of CO2 electroconversion into formate. These advantages make the Ov-engineered SnO2 electrocatalysts exhibit both a high Faraday efficiency (FE) of nearly 90% and a superior cathodic energy efficiency of above 60% to produce formate in a wide current range from 100 to 400 mA cm-2 in a flow cell. A commercially required current of 200 mA cm-2 can be obtained at only 2.8 V in a full cell. The present Ov engineering strategy exhibits the possibility for the design and construction of high-activity oxide-based electrocatalysts.

Oxygen and sulfur dual vacancy engineering on a 3D Co3O4/Co3S4heterostructure to improve overall water splitting activity

Oxygen, sulfur dual vacancy-rich Co3O4/Co3S4heterojunction nanoflowers were grown on nickel foam (DV-Co3O4/Co3S4@NF) using hydrothermal and reduction strategies and assembled as efficient bifunctional electrocatalysts for overall water splitting.

Oxygen vacancy and valence engineering in CeO2 through distinct sized ion doping and their impact on oxygen reduction reaction catalysis.

Defect tuning in ceria to enhance its catalytic properties is a subject of great interest for the scientific community owing to the growing demand for catalytic materials in drug, automobile and chemical industries. Doping induced defect engineering was found to be one of the most sought out strategies particularly in oxides for achieving multifunctionality. Here, in this study, we have doped ceria with distinct sized trivalent rare-earth ions, namely, Y3+, Eu3+ and La3+, using combustion techniques. Positron annihilation lifetime spectroscopy (PALS) suggested enhanced defect density with doping in general and higher concentration of oxygen vacancies in La3+ doped ceria compared to Y3+ and Eu3+ counterparts. X-ray photoelectron spectroscopy (XPS) suggested the existence of both Ce3+ and Ce4+, with the former having higher fraction in CeO2:La3+ compared to CeO2:Y3+. The electron transfer resistance (Rct) reduced in all the doped samples when compared to undoped ceria and they demonstrated improved catalytic activity towards the oxygen reduction reaction (ORR). The highest reduction in Rct was seen in the 5% La doped sample owing to the very high concentration of oxygen vacancies and Ce3+/Ce4+ ratio and CeO2:5.0% La3+ showed the best performance towards ORR electrocatalysis. The studies are expected to help in further tuning the catalysts in terms of dopant concentrations, and in future work, the strategy will be to control the Ce3+/Ce4+ ratio and see its implication in both catalytic and magnetic applications.