Oxygen Vacancy Engineering Research Articles

Modulating internal electric field by oxygen vacancy engineering and consequent forming quantum wells for boosted selective CO2 photoreduction

Although internal electric field of photocatalysts is considered as the potent driving force for efficient charge separation, modulating the internal electric field intensity remains a challenge. Herein, we considered that the internal electric field intensity of Sillén-structured bimetallic oxyhalide PbBiO2Cl could be modulated by tuning surface oxygen vacancy concentration, thereby influencing the corresponding charge transfer. In comparison to bulk PbBiO2Cl and PbBiO2Cl with deficient oxygen vacancies, the PbBiO2Cl with rich oxygen vacancies possessed enhanced internal electric field intensity due to its high oxygen vacancy concentrations, resulting in the primary charge separation spatially. Then the surface oxygen vacancies captured more dissociative electrons as quantum wells to promote the photocatalytic selective CO2-CO conversion. The mechanism was researched and verified by in-situ FTIR and DFT calculations. Using defect engineering to simultaneously modulate internal electric field and form quantum wells for promoting charge separation is an efficient strategy to rationally improve photocatalytic performances.

Oxygen Vacancies‐Rich Metal Oxide for Electrocatalytic Nitrogen Cycle

AbstractThe development of industry and agriculture has been accompanied by an artificially imbalanced nitrogen cycle, which threatens human health and ecological environments. Electrocatalytic systems have emerged as a sustainable way of converting nitrogen‐containing molecules into high value‐added chemicals. However, the construction of high‐performance electrocatalysts remains challenging. The development of oxygen vacancy engineering strategy has promoted more research efforts to explore the structure‐activity relationship between catalytic activity and oxygen vacancies. This review systematically summarizes the recent development of oxygen vacancies‐rich metal oxides for electro‐catalyzing nitrogen cycling systems, involving electrocatalytic nitrate reduction reaction, nitric oxide reduction reaction, nitrogen reduction reaction, C─N coupling, urea oxidation reaction, and nitrogen oxidation reaction. First, the construction methods and characterization methods of oxygen vacancies are summarized. Then, the effect of oxygen vacancy on electrocatalytic activity of metal oxides is discussed in terms of regulating the electronic structures of electrocatalysts, improving the electroconductivity of catalysts, lowing the energy barrier, and strengthening adsorption and activation of intermediate species. Finally, future directions for oxygen vacancy engineering and electrocatalytic nitrogen cycle are anticipated.

Piezoelectric Ba0.85 Sr0.15 TiO3 Nanosonosensitizer with Nitric Oxide Delivery for Boosting Cancer Therapy.

The efficacy of sonodynamic therapy (SDT) mainly relies on the sonosensitizers, which generate reactive oxygen species (ROS) upon ultrasound (US) stimulation. However, the limited availability of high-efficiency sonosensitizers hampers the therapeutic effectiveness of SDT as a standalone modality. In this work, a robust sonodynamic and gas cancer therapeutic platform is constructed based on strontium (Sr) doped barium titanate (BST) piezoelectric nanoparticles functionalized with L-arginine (BST@LA). The doping of Sr into A site of the ABO3 piezoelectric nanocrystals not only introduces oxygen vacancies into the nanoparticles and enhance the intrinsic piezoelectricity, but also narrows the semiconductor band gap and enhances charge carrier migration, all of which facilitate the sonodynamic production of superoxide anion (•O2 - ) and hydroxyl radical (•OH). In addition, the generated ROS promotes the decomposition of the surface-tethered LA, enabling the controlled release of nitric oxide (NO) gas at the tumor site, thereby achieving a combination therapeutic effect. In vivo experiments exhibit remarkable tumor suppression rate (89.5%) in 4T1 tumor mice model, demonstrating the effectiveness of this strategy. The ion doping and oxygen vacancy engineering to improve sonosensitizers, along with the synergistic combination of sonodynamic and gas therapy, provides promising avenues for improving cancer therapy.

Effect of rare earth substitution on electromagnetic and microwave absorption properties of nickel-cobalt nano ferrite

Oxygen vacancy engineering is one of the most effective strategies for tuning the microstructural properties of oxide nanomaterials. However, the connection between oxygen vacancies and electromagnetic (EM) wave absorption capacities is unclear. Herein, oxygen vacancy-boosted microwave absorption is realized over Gd-doped Ni0.5Co0.5Fe2O4 (NCFO) nanoceramics. All magnetic properties are studied with the influence of induced lattice strain. Except for Ni0.5Co0.5 Gd0.075Fe1.925O4 (NCFOG3), which has an elevated saturation magnetization (Ms) of 63 emu/g, the Ms decreases with increasing Gd content. In addition, remnant magnetization (Mr), coercivity (Hc), and anisotropic constant (K) increased until Ni0.5Co0.5 Gd0.050Fe1.95O4 (NCFOG2) and then declined. The EM wave parameters: dielectric permittivity (ϵ'), magnetic permeability (μ'), dielectric loss (ϵ''), and magnetic loss (μ'') are systematically examined and found in the ranges of 2.07–3.5, 1.73–4.7, (4 × 10-2) – (2.2 × 10-1) and 0.18–0.35 respectively. Our finding shows that a small amount of Gd favors the high oxygen vacancy concentration, an appropriate lattice defect, and high magnetic and dielectric losses. The possible mechanism for EM wave absorption revealed the largely localized electrons and dipole centers created by the numerous oxygen vacancies causing the multiple reflection and scattering, which enhanced conductive loss, defect, and dipole polarizations. The maximum reflection loss (RL) -28.37 dB is observed at 17.80 GHz of a 2 mm thick sample for NCFOG3. This research reveals a distinct link between oxygen vacancy defects and EM wave dissipation capability, providing important information for developing better EM wave absorbents.

Synergistic effect of electronic modulation and oxygen vacancy in Cu2O@CuNiMo heterostructure for accelerating alkaline electrocatalytic hydrogen evolution reaction

Electrochemical water splitting is an attractive chemical method for hydrogen generation with cleanliness and zero pollution. However, the reported catalysts are still unsatisfactory due to low electron transport efficiency and poor water splitting capacity. Herein, a high–performance oxygen vacancy–rich Cu2O–based heterostructure (Cu2O@CuNiMo) was constructed for solving these problems. The results of X–ray photoelectron spectroscopy and Raman suggested that there was strong electron transfer between CuNiMo and Cu2O, which could optimize the electronic structure. Electron paramagnetic resonance proved that there were abundant oxygen vacancies (OVS) on the surface of the Cu2O, which generated a mass of adsorbed hydrogen (Hads) by accelerating water splitting in an alkaline solution. Therefore, the Cu2O@CuNiMo electrocatalyst exhibits outstanding hydrogen evolution reaction (HER) performance with an ultra–low overpotential of 49 mV at a current density of 10 mA cm−2 in 1.0 M KOH electrolyte, outperforming many other previously reported transition metal–based catalysts. Moreover, Cu2O@CuNiMo exhibits exceptional durability for a 24–h long–term test at a current density of 200 mA cm−2. This work provides a promising method to design highly active HER electrocatalysts via the dual regulation strategy of oxygen vacancy engineering and electronic behavior.

Ultra-efficient electrooxidation of ethylene glycol enable by Pd-loaded Fe-doped Nb2O5 with abundant oxygen vacancies

Niobium pentoxide (Nb2O5) has emerged as a highly promising electrocatalyst for ethylene glycol oxidation reaction (EGOR) due to its eco-friendly nature and its ability to maintain structural stability in alkaline environments. However, its inherent electronic structure has posed a significant barrier to further enhancing of EGOR activity. In this study, we successfully synthesized Pd-based electrocatalysts by incorporating Fe-doped Nb2O5 with abundant oxygen vacancies (Pd/FNO-2.5), which effectively promoted ethylene glycol oxidation. The results showed that the introduction of Fe doping not only altered the electronic structure of Nb2O5, leading to the generation of oxygen vacancies, but also decreased the d-band center of Pd, thereby reducing thermodynamic energy barrier of the rate-determining step by approximately 0.58 eV. Impressively, the Pd/FNO-2.5 catalyst demonstrated remarkable electrocatalytic performance exhibiting a relatively low initial potential (−0.11 V) and high mass activity (0.380 A mg−1Pd). Furthermore, even after undergoing 100 consecutive recycling experiments, the Pd/FNO-2.5 catalyst still retained 81.10 % of its current density. This study demonstrates that doping-induced oxygen vacancy engineering is a promising approach for developing efficient EGOR electrocatalysts for direct ethylene glycol fuel cells, which is associating with the efficient and sustainable development of fuel cell and the carbon neutrality efforts.

Oxygen Defect and Cl--Doped Modulated TiNb2O7 Compound with High Rate Performance in Lithium-Ion Batteries.

TiNb2O7 has attracted extensive attention from lithium-ion battery researchers due to its superior specific capacity and safety. However, its poor ion conductivity and electron conductivity hinder its further development. To improve the ion/electron transport of TiNb2O7, we report that chlorine doping and oxygen vacancy engineering regulate the energy band and crystal structure simultaneously through a simple solid-phase method. NH4Cl was used to realize Cl- doping and oxygen vacancy production. A Rietveld refinement demonstrates an effective substitution of Cl in the O sites of Nb-O octahedra, with an enlarged crystal plane spacing. The oxygen vacancies provide more active sites for lithium intercalation. The diffusion coefficient of Li+ is inceased from 2.39 × 10-14 to 1.50 × 10-13 cm2 s-1, which reveals the positive influence of Cl- doping and oxygen vacancies on the promoted Li+ transport behavior. Charge compensation is introduced by the doping of Cl- and the generation of oxygen vacancies, leading to the formation of Ti3+ and Nb4+ and the adjustment of the electronic structure. DFT calculations reveal that TiNb2O7 with Cl- doping and an O vacancy shows a metallic property with a finite value at the Fermi level, which is conducive to electron transfer in the electrode material. Benefiting from these advantages, the modified TiNb2O7 presents superior rate performance with a commendable capacity of 172.82 mAh g-1 at 50 C. This work provides guidance to design high-performance anode materials for high-rate lithium-ion batteries.

High-Valence Mo Doping and Oxygen Vacancy Engineering to Promote Morphological Evolution and Oxygen Evolution Reaction Activity.

The rational design of high-efficiency, low-cost electrocatalysts for electrochemical water oxidation in alkaline media remains a huge challenge. Herein, combined strategies of metal doping and vacancy engineering are employed to develop unique Mo-doped cobalt oxide nanosheet arrays. The Mo dopants exist in the form of high-valence Mo6+, and the doping amount has a significant effect on the structure morphology, which transforms from 1D nanowires/nanobelts to 2D nanosheets and finally 3D nanoflowers. In addition, the introduction of vast oxygen vacancies helps to modulate the electronic states and increase the electronic conductivity. The optimal catalyst MoCoO-3 exhibits greatly increased active sites and enhanced reaction kinetics. It gives a dramatically lower overpotential at 50 mA cm-2 (288 mV), much smaller than that of the undoped counterpart (418 mV) and comparable to those of the recently reported electrocatalysts. Density functional theory results further verify that the increased electronic conductivity and optimized adsorption energy toward oxygen evolution reaction intermediates are mainly responsible for the enhanced catalytic activity. Moreover, the assembled two-electrode electrolyzer (MoCoO-3||Pt/C) exhibits superior performance with the cell potential decreased by 233 mV to reach a current density of 50 mA cm-2 with respect to the benchmark counterpart catalysts (RuO2||Pt/C). This work might contribute to the rational design of effective, low-cost electrocatalyst materials by combining multiple strategies.

Relationship between defect and strain in oxygen vacancy-engineered TiO2 towards photocatalytic H2 generation

Photocatalytic H2 generation is an effective approach to convert solar energy into renewable H2 energy and has drawn great attentions. To improve the catalytic activity, lots of attentions have been paid to developing advanced strategies, of which oxygen vacancy engineering is considered as a promising one. However, oxygen vacancy induced coexistence of defect and strain makes understanding the essential mechanism of enhanced photocatalytic performance elusive and challenging. Here, the classic photocatalyst TiO2 is selected as a paradigm to reveal the relationship between the accompanied defect and strain in boosting H2 generation activity. It is found that oxygen vacancy concentration almost shows a volcano-type trend, while strain exhibits a monotonic decrease with increasing the calcination temperature. An optimal photocatalytic H2 yield of 788 μmol g−1 h−1 is achieved over the TiO2 with high oxygen vacancy concentration but slight strain. This value is 2.5 times higher than the counterpart with low oxygen vacancy concentration and large strain, indicating that oxygen vacancy induced defect instead of strain plays the dominate role in enhancing photocatalytic H2 generation, which is further verified by theoretical calculations and experimental carrier dynamics analysis. This work uncovers the relationship between defect and strain in oxygen vacancy-engineered photocatalysts.

Engineering oxygen vacancies in Bi2WO6 by introducing heteroatoms for enhancing photo-oxidation/reduction activities

To improve the light-harvesting capability and electron-hole separation efficiency, a novel heteroatom-introduced Bi2WO6 photocatalyst (OV–Bi2WO6) with oxygen vacancies (OVs) was prepared via the partial substitution of O2− by S2− anions. The OV-Bi2WO6 showed high photocatalytic properties in photo-oxidation/reduction reactions under visible-light. The OVs content could be controlled by adjusting the sulfur source amount, and the optimal OV(0.9)-Bi2WO6 with suitable OVs had a high photocatalytic activity with 97.6% of MO removal and 88.2% of Cr(VI) removal efficiency. Density functional theory (DFT) calculations verified that the OVs in Bi2WO6 could induce a new defect level to decrease the bandgap energy and accelerate the carrier separation/migration. Furthermore, the possible photocatalytic mechanisms for MO degradation and Cr(VI) reduction over the OV-Bi2WO6 were proposed, respectively. The present work helped us to better understand the enhancement mechanism of OVs in Bi-based semiconductors and paved the way to develop high-performance photocatalysts for environmental remediation.

Ultrahigh Piezocatalytic Performance of Perovskite Ferroelectric Powder via Oxygen Vacancy Engineering.

Piezocatalysis has increasingly gained prominence due to its enormous potential for addressing energy shortages and environmental pollution issues. Nonetheless, the low piezocatalytic activity of state-of-the-art materials seriously inhibits the practical applications of piezocatalysis. Here, itis proposed to greatly enhance the piezocatalytic activity for a perovskite ferroelectric, i.e., Sm-doped 0.68Pb(Mg1/3 Nb2/3 )-0.32PbTiO3 (Sm-PMN-PT, a solid solution with ultrahigh piezoelectricity), by introducing oxygen vacancies (OVs). The results show that the presence of OVs promotes the production of reactive oxygen species while enhancing the adsorption and activation of organic pollutants to improve piezocatalytic performance. The OV-Sm-PMN-PT is found to possess a superior piezocatalytic degradation rate constant of 0.073 min-1 under ultrasonic vibration, which is ≈4.9 times higher than that of pristine Sm-PMN-PT. Furthermore, the OV-Sm-PMN-PT can efficiently remove RhB under 400rpm stirring, making it a promising candidate for water purification using low-frequency mechanical energy from nature. This research sheds light on the design of piezocatalytic materials via defect engineering.

Cationic and anionic defect decoration of CoO through Cu dopants and oxygen vacancy for a High‑Performance supercapacitor

CoO has attracted increasing attention as an electrochemical energy storage owing to its excellent redox activity and high theoretical specific capacitance. However, its low inherent electrical conductivity results in sluggish reaction kinetics, and the poor rate capability of CoO limits its widespread applications. Herein, a multiple-defect strategy of engineering oxygen vacancies and Cu-ion dopants into the low-crystalline CoO nanowires (Ov–Cu–CoO) is successfully applied. Because of the advantage of the dual defect synergetic effect, the electronic structure and charge distribution are effectively modulated, thus enhancing the electrical conductivity and enriched redox chemistry. The obtained Ov–Cu–CoO electrode exhibits a high specific capacity of 1388.6 F⋅g−1 at a current density of 1 A⋅g−1, an ultrahigh rate performance (81.2% of the capacitance retained at 20 A⋅g−1) and excellent cycling stability (101.1% after 10,000 cycles). Moreover, an asymmetric supercapacitor device with Ov–Cu–CoO as the positive electrode having a high energy density of 44.1 W⋅h⋅kg−1 at a power density of 800 W⋅kg−1, and can still remain 27.2 W⋅h⋅kg−1 at a power density of 16 kW⋅kg−1. This study demonstrates an effective strategy to enhance electrochemical performance of CoO that can be easy applied to other transition metal oxides.

Oxygen vacancies in MnOx regulating reaction kinetics for aqueous zinc-ion batteries

MnO2 cathode materials have presented challenges due to their poor conductivity, unstable structure, and sluggish diffusion kinetics for aqueous zinc-ion batteries (AZIBs). In this study, a nanostructured MnOx cathode material was synthesized using an acid etching method, Which introduced abundant Mn(III) sites, resulting in the formation of numerous oxygen vacancies. Comprehensive characterizations revealed that these oxygen vacancies facilitated the reversible adsorption/desorption of Zn2+ ions and promoted efficient electron transfer. In addition, the designed mesoporous structure offered ample active sites and shortened the diffusion path for Zn2+ and H+ ions. Consequently, the nanosized MnOx cathode exhibited enhanced reaction kinetics, achieving a considerable reversible specific capacity of 388.7 mAh/g at 0.1 A/g and superior durability with 72.0% capacity retention over 2000 cycles at 3.0 A/g. The material delivered a maximum energy density of 639.7 Wh kg−1 at 159.94 W kg−1. Furthermore, a systematic analysis of the zinc storage mechanism was performed. This work demonstrates that engineering oxygen vacancies with nanostructure regulation provides valuable insights into optimizing MnO2 cathode materials for AZIBs.

Engineering oxygen vacancies in perovskite oxides by in-situ electrochemical activation for highly efficient nitrate reduction

Perovskite oxides have emerged as a new category of catalysts for NO3RR, yet their low intrinsic catalytic activity results in unsatisfactory performance. Oxygen vacancy engineering has recently been found to be effective for improving the NO3RR performance of perovskite oxides. Herein, a novel and efficient strategy of electrochemical activation for in-situ oxygen vacancies (OVs) creation in perovskite oxide La0.9FeO3-δ was reported. The results showed that the NO3−-N removal rate increased 2.6-fold on activated La0.9FeO3-δ in comparison to pristine La0.9FeO3-δ. The enhanced NO3RR performance was attributed to the presence of more OVs, which served to increase the adsorption energy of NO3− while also promoting atomic H* formation for NO3−-N hydrogenation. Furthermore, a continuous experiment lasting 240 h found the activated La0.9FeO3-δ exhibited extremely high stability. Additionally, we demonstrated that the electrochemical activation method was applicable to other typical perovskite oxides, such as LaCoO3, indicating its generalizability. This study provides a simple and scalable approach for the preparation of a high-performance perovskite oxide-type electrocatalysts for NO3RR.

Turning Silica into Enzymes by Hydrogenation: Simultaneously Achieving Oxygen Vacancy Engineering and Tumor Adaptive Accumulation for NIR‐II‐Potentiated Therapy

AbstractMolybdenum (Mo)‐based nanozymes have been attracting increasingly extensive attention in photocatalytic antitumor field due to their versatile physicochemical properties, whereas the limited light capture rate and high recombination rate of photogenerated carriers seriously impedes their further development. Herein, MoO3‐starring silica nanozymes with hyaluronic acid modification (HMMSNs@HA) are innovated by hydrogenation to simultaneously achieve oxygen vacancies (OVs) engineering and tumor adaptive accumulation for the second near‐infrared (NIR‐II, 1064 nm) light‐potentiated thermal‐catalytic therapy. The hydrogenation‐regulated OVs can narrow the band gap of HMMSNs from 2.66 to 1.16 eV, achieving optimal optical absorption in NIR‐II region. Additionally, HMMSNs hold high separation efficacy of electron‐hole pairs to facilitate the generation of reactive oxygen species under laser irradiation. Significantly, HMMSNs@HA are stable in tumor microenvironment, while can degrade in normal physiological conditions, thereby offering tumor‐adaptive accumulation. Synchrotron radiation‐based extended X‐ray absorption fine structure spectroscopy reveals that OVs enabling the Mo4+ and Mo5+ formation, which can react with tumor endogenous H2O2 to produce hydroxyl radicals. Furthermore, OVs‐induced localized surface plasmon resonance effect endows the nanozymes with photothermal conversion efficacy of 32.3%, which affords NIR‐II‐excited photonic hyperthermia‐enhances catalytic therapy. All the experimental results demonstrate the high safety and superiorities of HMMSNs@HA for NIR‐II‐initiate therapy.

Oxygen vacancy engineering on copper-manganese spinel surface for enhancing toluene catalytic combustion: A comparative study of acid treatment and alkali treatment

Copper-manganese spinel is a low-cost VOCs catalytic combustion catalyst with good performance. Oxygen vacancy has excellent properties for oxygen activation and VOCs dehydrogenation activation, which is beneficial for the catalytic combustion of VOCs. In this study, a large number of oxygen vacancies were introduced on the copper-manganese spinel surface by selective dissolution method (acid treatment and alkali treatment) for catalytic combustion of toluene. Furthermore, the effects of acid treatment and alkali treatment on the catalytic performance, oxygen vacancy amount, physical and chemical properties, and toluene catalytic combustion mechanism of copper-manganese spinel were studied. Both acid treatment and alkali treatment can produce large quantities of oxygen vacancies on the copper-manganese spinel surface. The generation of surface oxygen vacancies can greatly improve the catalytic combustion activity of copper-manganese spinel. At 240 °C, the combustion rate of toluene increased by 8.8 times for the acid-treated catalyst and 11.2 times for the alkali-treated catalyst. The numerous surface oxygen vacancies, Mn3+/Mn4+ at the ratio of 1.11 and appropriate acidity result in the alkali-treated catalyst exhibiting excellent catalytic activity and stability for toluene combustion. This strategy provides a new method to further improve catalytic combustion activity of copper-manganese spinel and a reference for the development of the surface oxygen vacancy engineering of transition metal oxides.

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.