Dynamic investigation of oxygen defects on transition metal-based electrocatalysts:formation,characterization,and mechanism during alkaline oxygen evolution reaction

Oxygen defects play a critical role in the electrocatalytic oxygen evolution reaction(OER).Therefore,in-depth understanding the structure-activity-mechanism relationship of these defects is the key to design efficient OER electrocatalysts.This relationship needs to be understood dynamically due to the potential for irreversible phase transitions during OER.Consequently,significant efforts have been devoted to study the dynamic evolution of oxygen defects to shed light on the OER mechanism.This review critically examines and analyzes the dynamic processes occurring at oxygen defect sites during OER,including defect formation and defect evolution mechanisms,along with the advanced characterization techniques needed to understand these processes.This review aims to provide a comprehensive understanding of high-efficiency electrocatalysts,with a particular emphasis on the importance of in situ monitoring the dynamic evolution of oxygen defects,providing a new perspective towards efficient OER electrocatalyst design.

Introducing Ce ions and oxygen defects into V_(2)O_(5)nanoribbons for efficient aqueous zinc ion storage

Cost-effectively,eco-friendly rechargeable aqueous zinc-ion batteries(AZIBs)have reserved widespread concerns and become outstanding candidate in energy storage systems.However,the progress pace of AZIBs suffers from limitation of suitable and affordable cathode materials.Herein,a double-effect strategy is realized in a one-step hydrothermal treatment to prepare V_(2)O_(5)nanoribbons with intercalation of Ce and introduction of abundant oxygen defects(Od-Ce@V_(2)O_(5))to enhance electrochemical performance synergistically.Coupled with the theoretical calculation results,the introduction of Ce ions intercalation and oxygen vacancies in V2O5 structure enhances the electrical conductivity,reduces the adsorption energy of zinc ions,enlarges the interlayer distance,renders the structure more stable,and facilitates rapid diffusion kinetics.As expected,the desirable cathode delivers the reversible capacity of 444 mAh·g^(−1)at 0.5 A·g^(−1)and shows excellent Coulombic efficiency,as well as an extraordinary energy density of 304.9 Wh·kg^(−1).The strategy proposed here may aid in the further development of cathode materials with stable performance for AZIBs.

Oxygen-defects evolution to stimulate continuous capacity increase in Co-free Li-rich layered oxides

Though oxygen defects are associated with deteriorated structures and aggravated cycling performance in traditional layered cathodes,the role of oxygen defects is still ambiguous in Li-rich layered oxides due to the involvement of oxygen redox.Herein,a Co-free Li-rich layered oxide Li_(1.286)Ni_(0.071)Mn_(0.643)O_(2)has been prepared by a co-precipitation method to systematically investigate the undefined effects of the oxygen defects.A significant O_(2)release and the propagation of oxygen vacancies were detected by operando differential electrochemical mass spectroscopy(DEMS)and electron energy loss spectroscopy(EELS),respectively.Scanning transmission electron microscopy-high angle annular dark field(STEMHAADF)reveals the oxygen vacancies fusing to nanovoids and monitors a stepwise electrochemical activation process of the large Li_(2)MnO_(3)domain upon cycling.Combined with the quantitative analysis conducted by the energy dispersive spectrometer(EDS),existed nano-scale oxygen defects actually expose more surface to the electrolyte for facilitating the electrochemical activation and subsequently increasing available capacity.Overall,this work persuasively elucidates the function of oxygen defects on oxygen redox in Co-free Li-rich layered oxides.

Oxygen defects boost polysulfides immobilization and catalytic conversion:First-principles computational characterization and experimental design

Although some experiments have shown that point defects in a cathode host material may enhance its performance for lithium-sulfur battery(LSB),the enhancement mechanism needs to be well investigated for the design of desired sulfur host.Herein,the first principle density functional theory(DFT)is adopted to investigate a high-performance sulfur host material based on oxygen-defective TiO2(D-TiO2).The adsorption energy comparisons and Gibbs free energy analyses verify that D-TiO2 has relatively better performances than defect-free TiO2 in terms of anchoring effect and catalytic conversion of polysulfides.Meanwhile,D-TiO2 is capable of absorbing the most soluble and diffusive long-chain polysulfides.The newly designed D-TiO2 composited with three-dimensional graphene aerogel(D-TiO2@Gr)has been shown to be an excellent sulfur host,maintaining a specific discharge capacity of 1,049.3 mAhg^−1 after 100 cycles at 1C with a sulfur loading of 3.2 mgcm^−2.Even with the sulfur mass loading increasing to 13.7 mgcm^−2,an impressive stable cycling is obtained with an initial areal capacity of 14.6 mAhcm^−2,confirming the effective enhancement of electrochemical performance by the oxygen defects.The DFT calculations shed lights on the enhancement mechanism of the oxygen defects and provide some guidance for designing advanced sulfur host materials.

In-situ oriented oxygen-defect-rich Mn-N-O via nitridation and electrochemical oxidation based on industrial-scale Mn_(2)O_(3) to achieve high-performance aqueous zinc ion battery

As a general problem in the field of batteries,materials produced on a large industrial scale usually possess unsatisfactory electrochemical performances.Among them,manganese-based aqueous rechargeable zinc-ion batteries(ARZBs)have been emerging as promising large-scale energy storage systems owing to their high energy densities,low manufacturing cost and intrinsic high safety.However,the direct application of industrial-scale Mn2O3(MO)cathode exhibits poor electrochemical performance especially at high current rates.Herein,a highly reversible Mn-based cathode is developed from the industrial-scale MO by nitridation and following electrochemical oxidation,which triples the ion diffusion rate and greatly promotes the charge transfer.Notably,the cathode delivers a capacity of 161 m Ah g^(-1) at a high current density of 10 A g^(-1),nearly-three times the capacity of pristine MO(60 m Ah g^(-1)).Impressive specific capacity(243.4 m Ah g^(-1))is obtained without Mn^(2+) additive added in the electrolyte,much superior to the pristine MO(124.5 m Ah g^(-1)),suggesting its enhanced reaction kinetics and structural stability.In addition,it possesses an outstanding energy output of 368.4 Wh kg^(-1) at 387.8 W kg^(-1),which exceeds many of reported cathodes in ARZBs,providing new opportunities for the large-scale application of highperformance and low-cost ARZBs.

Oxygen‑Deficient β‑MnO_(2)@Graphene Oxide Cathode for High‑Rate and Long‑Life Aqueous Zinc Ion Batteries

Recent years have witnessed a booming interest in grid-scale electrochemical energy storage,where much attention has been paid to the aqueous zinc ion batteries(AZIBs).Among various cathode materials for AZIBs,manganese oxides have risen to prominence due to their high energy density and low cost.However,sluggish reaction kinetics and poor cycling stability dictate against their practical application.Herein,we demonstrate the combined use of defect engineering and interfacial optimization that can simultaneously promote rate capability and cycling stability of MnO_(2) cathodes.β-MnO_(2) with abundant oxygen vacancies(VO)and graphene oxide(GO)wrapping is synthesized,in which VO in the bulk accelerate the charge/discharge kinetics while GO on the surfaces inhibits the Mn dissolution.This electrode shows a sustained reversible capacity of~129.6 mAh g^(−1) even after 2000 cycles at a current rate of 4C,outperforming the state-of-the-art MnO_(2)-based cathodes.The superior performance can be rationalized by the direct interaction between surface VO and the GO coating layer,as well as the regulation of structural evolution ofβ-MnO_(2) during cycling.The combinatorial design scheme in this work offers a practical pathway for obtaining high-rate and long-life cathodes for AZIBs.

Oxygen defect-rich double-layer hierarchical porous Co3O4 arrays as high-efficient oxygen evolution catalyst for overall water splitting

Construction of oxygen evolution electrocatalysts with abundant oxygen defects and large specific surface areas can significantly improve the conversion efficiency of overall water splitting.Herein,we adopt a controlled method to prepare oxygen defect-rich double-layer hierarchical porous Co3O4 arrays on nickel foam(DL-Co3O4/NF)for water splitting.The unique array-like structure,crystallinity,porosity,and chemical states have been carefully investigated through SEM,TEM,XRD,BET,and XPS techniques.The designated DL-Co3O4/NF has oxygen defects of up to 67.7%and a large BET surface area(57.4 m2g-1).Electrochemical studies show that the catalyst only requires an overpotential of 256 mV to reach 20 mA cm-2,as well as a small Tafel slope of 60.8 mV dec-1,which is far better than all control catalysts.Besides,the catalyst also demonstrates excellent overall water splitting performance in a two-electrode system and good long-term stability,far superior to most previously reported catalysts.Electrocatalytic mechanisms indicate that abundant oxygen vacancies provide more active sites and good conductivity.At the same time,the unique porous arrays facilitate electrolyte transport and gas emissions,thereby synergistically improving OER catalytic performance.

Tunable oxygen defect density and location for enhancement of energy storage

Defect engineering is in the limelight for the fabrication of electrochemical energy storage devices.However,determining the influence of the defect density and location on the electrochemical behavior remains challenging.Herein,self-organized TiO_(2)nanotube arrays(TNTAs)are synthesized by anodization,and their oxygen defect location and density are tuned by a controllable post-annealing process.TNTAs annealed at 600℃ in N2 exhibit the highest capacity(289.2 m Ah g^(-1)at 0.8 C)for lithium-ion storage,while those annealed at 900℃ in N2 show a specific capacitance of 35.6 m F cm^(-2)and stability above96%after 10,000 cycles for supercapacitor.Ex situ electron paramagnetic resonance spectra show that the surface-exposed oxygen defects increase,but the bulk embedded oxygen defects decrease with increasing annealing temperature.Density functional theory simulations reveal that a higher density of bulk oxygen defects corresponds to higher localized electrons states,which upshift the Fermi level and facilitate the lithium intercalation kinetic process.Meanwhile,differential charge density calculation indicates that the increase of surface oxygen defects in the anatase(101)plane leads to higher density excess electrons,which act as negative charge centers to enhance the surface potential for ion adsorption.This oxygen-deficient location and density tunable strategy introduce new opportunities for high-energy and high-power-density energy storage systems.

Oxygen‑Defect Enhanced Anion Adsorption Energy Toward Super‑Rate and Durable Cathode for Ni–Zn Batteries

The alkaline zinc-based batteries with high energy density are becoming a research hotspot.However,the poor cycle stability and low-rate performance limit their wide application.Herein,ultra-thin CoNiO2 nanosheet with rich oxygen defects anchored on the vertically arranged Ni nanotube arrays(Od-CNO@Ni NTs)is used as a positive material for rechargeable alkaline Ni–Zn batteries.As the highly uniform Ni nanotube arrays provide a fast electron/ion transport path and abundant active sites,the Od-CNO@Ni NTs electrode delivers excellent capacity(432.7 mAh g^(−1))and rate capability(218.3 mAh g^(−1) at 60 A g^(−1)).Moreover,our Od-CNO@Ni NTs//Zn battery is capable of an ultra-long lifespan(93.0%of initial capacity after 5000 cycles),extremely high energy density of 547.5 Wh kg^(−1) and power density of 92.9 kW kg^(−1)(based on the mass of cathode active substance).Meanwhile,the theoretical calculations reveal that the oxygen defects can enhance the interaction between electrode surface and electrolyte ions,contributing to higher capacity.This work opens a reasonable idea for the development of ultra-durable,ultra-fast,and high-energy Ni–Zn battery.

Oxygen vacancies enriched nickel cobalt based nanoflower cathodes: Mechanism and application of the enhanced energy storage

The rational design of oxygen vacancies and electronic microstructures of electrode materials for energy storage devices still remains a challenge. Herein, we synthesize nickel cobalt-based oxides nanoflower arrays assembled with nanowires grown on Ni foam via the hydrothermal process followed annealing process in air and argon atmospheres respectively. It is found that the annealing atmosphere has a vital influence on the oxygen vacancies and electronic microstructures of resulting NiCo_(2)O_(4) (NCO-Air) and CoNiO_(2) (NCO-Ar) products, which NCO-Ar has more oxygen vacancies and larger specific surface area of 163.48 m^(2)/g. The density functional theory calculation reveals that more oxygen vacancies can provide more electrons to adsorb –OH free anions resulting in superior electrochemical energy storage performance. Therefore, the assembled asymmetric supercapacitor of NCO-Ar//active carbon delivers an excellent energy density of 112.52 Wh/kg at a power density of 558.73 W/kg and the fabricated NCO-Ar//Zn battery presents the specific capacity of 180.20 mAh/g and energy density of 308.14 Wh/kg. The experimental measurement and theoretical calculation not only provide a facile strategy to construct flower-like mesoporous architectures with massive oxygen vacancies, but also demonstrate that NCO-Ar is an ideal electrode material for the next generation of energy storage devices.

Synergy in magnetic Ni_(x)Co_(1)O_(y) oxides enables base-free selective oxidation of 5-hydroxymethylfurfural on loaded Au nanoparticles

The base-free aerobic oxidation of 5-hydroxymethylfurfural(HMF) to 2,5-furandicarboxylic acid(FDCA)in water is recognized as an important and sustainable upgrading process for cellulosic carbohydrates.However,selectivity control still remains a challenge.Here,we disclose that the unique synergy in magnetic Ni_(x)Co_(1)O_(y)(x=1,3 and 5) bimetallic oxides can induce reactive oxygen defects and simultaneously stabilize small-sized metallic Au nanoparticles in the Au/Ni_(x)Co_(1)O_(y)catalysts.Such catalytic features render effective adsorption and activation of O_(2),OH and C=O groups,realizing selective oxidation of HMF to FDCA.On a series of magnetic Au/Ni_(x)Co_(1)O_(y)catalysts with almost identical Au loadings(ca.0.5 wt%) and particle sizes(ca.2.7 nm),the variable Ni/Co molar ratios give rise to the tunable electron density of Au sites and synergistic effect between NiO and CoO_(y).The initial conversion rates of HMF and its derived intermediates(i.e., DFF,HMFCA and FFCA) show a volcano-like dependence on the number of oxygen defects(i.e.,O_(2)^(-)and O^(-)) and electron-rich Au0sites.The optimum Au/Ni3Co1Oycatalyst exhibits a highest productivity of FDCA(12.5 mmol_(FDCA)mol_(Au)^(-1)h^(-1)) among all the Au catalysts in the literature and achieves> 99% yield of FDCA at 120℃ and 10 bar of O_(2).In addition,this catalyst can be easily recovered by a magnet and show superior stability and reusability during six consecutive cycling tests.This work may shed a light on Au catalysis for the base-free oxidation of biomass compounds by smartly using the synergy in bimetallic oxide carriers.

Constructing oxygen deficiency-rich V_(2)O_(3)@PEDOT cathode for high-performance aqueous zinc-ion batteries

Aqueous zinc-ion batteries(AZIBs)have attracted widespread attention due to the advantages of high safety and environmental friendliness.Although V_(2)O_(3) is a promising cathode,the strong electrostatic interaction between Zn^(2+) and V_(2)O_(3) crystal,and the sluggish reaction kinetics still limit their application in AZIBs.Herein,the oxygen defects rich V_(2)O_(3) with conducive poly(3,4-ethylenedioxythiophene)(PEDOT)shell(V_(2)O_(3)-Od@PEDOT)was fabricated for AZIBs by combining the sulfur-assisted thermal reduction and in-situ polymerization method.The introduced oxygen vacancies of V_(2)O_(3)–Od@PEDOT weaken the electrostatic interaction between Zn^(2+) and the host material,improving the interfacial electron transport,while the PEDOT coating enhances the structural stability and conductivity of V_(2)O_(3),thus accelerating the reaction kinetics.Based on the advantages,V_(2)O_(3)–Od@PEDOT electrode delivers a reversible capacity of 495 mAh·g^(−1) at 0.1 A·g^(−1),good rate capability(189 mAh·g^(−1)at 8.0 A·g^(−1)),and an impressive cycling stability with 90.1%capacity retention over 1000 cycles at 8.0 A·g^(−1).The strategy may provide a path for exploiting the other materials for high performance AZIBs.

Ultrafine MoO_(x)clusters anchored on g-C_(3)N_(4)with nitrogen/oxygen dual defects for synergistic efficient O_(2)activation and tetracycline photodegradation

Photocatalytic O_(2)activation to generate reactive oxygen species is crucially important for purifying organic pollutants,yet remains a challenge due to poor adsorption of O_(2)and low efficiency of electron transfer.Herein,we demonstrate that ultrafine MoO_(x)clusters anchored on graphitic carbon nitride(g-C_(3)N_(4))with dual nitrogen/oxygen defects promote the photocatalytic activation of O_(2)to generate·O_(2)−for the degradation of tetracycline hydrochloride(TCH).A range of characterization techniques and density functional theory(DFT)calculations reveal that the introduction of the nitrogen/oxygen dual defects and MoO_(x)clusters enhances the O_(2)adsorption energy from−2.77 to−2.94 eV.We find that MoO_(x)clusters with oxygen vacancies(Ov)and surface Ov-mediated Moδ+(3≥δ≥2)possess unpaired localized electrons,which act as electron capture centers to transfer electrons to the MoO_(x)clusters.These electrons can then transfer to the surface adsorbed O_(2),thus promoting the photocatalytic conversion of O_(2)to·O_(2)−and,simultaneously,realizing the efficient separation of photogenerated electron–hole pairs.Our fully-optimized MoO_(x)/g-C_(3)N_(4)catalyst with dual nitrogen/oxygen defects manifests outstanding photoactivities,achieving 79%degradation efficiency toward TCH within 120 min under visible light irradiation,representing nearly 7 times higher activity than pristine g-C_(3)N_(4).Finally,based on the results of liquid chromatograph mass spectrometry and DFT calculations,the possible photocatalytic degradation pathways of TCH were proposed.

Defect-rich Mg-Al MMOs supported TEPA with enhanced charge transfer for highly efficient and stable direct air capture

Due to the advantages of low energy consumption and high CO_(2) selectivity, the development of solid amine-based materials has been regarded as a hot research topic in the field of DAC for the past decades.The adsorption capacity and stability over multiple cycles have been the top priorities for evaluation of practical application value. Herein, we synthesized a novel DAC material by loading TEPA onto defect-rich Mg_(0.55)Al-O MMOs with enhanced charge transfer effect. The optimal Mg_(0.55)Al-O-TEPA67% demonstrates the highest CO_(2)uptake of(3.0 mmol g^(-1)) and excellent regenerability, maintaining ~90% of the initial adsorption amount after 80 adsorption/desorption cycles. The in situ DRIFTS experiments suggested the formation of bicarbonate species under wet conditions. DFT calculations indicated that the stronger bonding between Mg_(0.55)Al-O support and solid amine was caused by the abundance of oxygen defects on MMOs confirmed by XPS and ESR, which favors the charge transfer between the support and amine,resulting in intense interaction and excellent regenerability. This work for the first time conducted comprehensive and systematic investigation on the stabilization mechanism for MMOs supported solid amine adsorbents with highest uptake and superior cyclic stability in depth, which is different from the most popular SiO_(2)-support, thus providing facile strategy and comprehensive theoretical mechanism support for future research about DAC materials.

Achieving high-performance multilayer MoSe2 photodetectors by defect engineering

Optoelectronic properties of MoSe2 are modulated by controlled annealing in air.Characterizations by Raman spectroscopy and XPS demonstrate the introduction of oxygen defects.Considerable increase in electron and hole mobilities reveals the highly improved electron and hole transport.Furthermore,the photocurrent is enhanced by nearly four orders of magnitudes under 7 nW laser exposure after annealing.The remarkable enhancement in the photoresponse is attributed to an increase in hole trapping centers and a reduction in resistance.Furthermore,the annealed photodetector shows a fast time response on the order of 10 ms and responsivity of 3×10^(4) A/W.

Simultaneously tuning structural defects and crystal phase in accordion-like Ti_(x)O_(2x−1)derived from Ti_(3)C_(2)T_(x)MXene for enhanced electromagnetic attenuation

Single Ti_(3)C_(2)T_(x)MXene(MTO)materials are not suitable for electromagnetic(EM)wave absorption due to their high conductivity and impedance mismatch.To address this issue,we ingeniously took advantage of easily oxidized characteristics of Ti_(3)C_(2)T_(x)MXene to establish structural defects and multiphase engineering in accordion-like TixO_(2x−1)derived from Ti_(3)C_(2)T_(x)MXene by a high-temperature hydrogen reduction process for the first time.Phase evolution sequences are revealed to be Ti_(3)C_(2)T_(x)MXene/anatase TiO_(2)→Ti_(3)C_(2)T_(x)MXene/rutile TiO_(2)→TixO_(2x−1)(1≤x≤4)during a hydrogen reduction reaction.Benefiting from conductance loss caused by hole motion under the action of an external electric field and heterointerfaces caused by interfacial polarization,the impedance match and EM attenuation capability of accordion-like TixO_(2x−1)absorbers derived from Ti_(3)C_(2)T_(x)MXene are superior to that of pristine Ti_(3)C_(2)T_(x)MXene/TiO_(2)materials.Additionally,simulated whole radar cross section(RCS)plots in different incident angular of the Ti_(3)C_(2)T_(x)MXene/rutile TiO_(2)product are lower than−20 dBm^(2),and the minimum RCS value can reach−43 dBm^(2),implying a great potential for practical applications in the EM wave absorption.Moreover,the relationship among charges,defects,interfaces,and EM performances in the accordion-like TixO_(2x−1)materials is systematically clarified by the energy band theory,which is suitable for the research of other MXene-derived semiconductor absorbing composites.

Oxygen-deficient ammonium vanadate/GO composites with suppressed vanadium dissolution for ultra-stable high-rate aqueous zinc-ion batteries

The structural engineering of hydrated ammonium vanadate as a cathode for aqueous Zn-ion batteries has attracted significant research interest because of its ability to suppress vanadium dissolution and accelerate the electrochemical dynamics.Herein,a feasible fabrication strategy for oxygen-deficient(NH_(4))_(2)V_(10)O_(25)·xH_(2)O/GO(NVOH@GO)composites was proposed,and the charge storage mechanism was discussed.The results of characterization analysis showed that the introduction of graphene oxide(GO)not only enlarged the layer spacing and improved electrical conductivity,providing spacious channels for Zn^(2+)(de)intercalation and accelerating the ion diffusion dynamics,but also induced more oxygen vacancies,inhibited the dissolution of vanadium,and reduced self-discharging,offering additional and stable active sites for ion storage.The optimized NVOH@GO electrode delivered extraordinarily stable capacities of 334 mAh·g^(-1)after 2000 cycles at 5 A·g^(-1)and 238 mAh·g^(-1)after 10,000cycles at 20 A·g^(-1).Furthermore,ex-situ X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS),and Raman results systematically revealed the electrochemical mechanism,including a phase transition reaction and subsequent Zn^(2+)/H_(2)O co-(de)intercalation process.This study provides an effective strategy for expanding the interlayer spacing,inducing defect engineering,and enhancing the structural stability of vanadium-based cathodes for Zn-ion batteries and other multivalent aqueous ion batteries.

Assisting Ni catalysis by CeO_(2) with oxygen vacancy to optimize the hydrogen storage properties of MgH_(2)

Although MgH_(2) has been widely regarded as a promising material for solid-state hydrogen storage,its high operating temperature and slow kinetics pose a major bottleneck to its practical application.Here,a nanocomposite catalyst with interfacial coupling and oxygen defects,Ni/CeO_(2),is fabricated to promote H_(2) desorption and absorption properties of MgH_(2).The interface of Ni/CeO_(2) contributes to both strong mechanical coupling towards stabilizing partial Ni and electronic coupling towards inducing a high con-centration of oxygen vacancies in CeO_(2).Theoretical calculations evidence that CeO_(2) with oxygen vacancy assist Ni in weakening the energy of Mg-H bond as well as enhancing the adsorption energy of Ni upon hydrogen atoms,and the extent of this assistance surprisingly increases with increasing oxygen vacancies concentration.As a result,an impressive performance is achieved by MgH_(2)-5 wt.%Ni/CeO_(2) with onset desorption temperature of only 165°C,and it absorbs approximately 80%hydrogen in just 800 s at 125°C.The generation mechanism of intermediate active species concerning Ni/CeO_(2) in different states has been analyzed for the first time,and the relationship between interfacial coupling and phase evolution has been elucidated.Therefore,a mechanism of the catalysis-assisting effect regarding oxygen defects is proposed.It is believed that this work provides a unique perspective on the mechanism of interfacial coupling and the generation of defects in composite catalysts.

Significantly enhanced piezoelectric performance in Bi_(4)Ti_(3)O_(12)-based high-temperature piezoceramics via oxygen vacancy defects tailoring

Bismuth titanate (Bi_(4)Ti_(3)O_(12),BIT)piezoelectric materials have attracted increasing attention due to their high-temperature applications.However,it is quite challenging to simultaneously achieve outstanding piezoelectric properties and high Curie temperature in BIT-based systems.In this study,oxygen vacancy defects tailoring strategy was utilized to solve this problem,excellent piezoelectric coefficient(32.1 pC/N),and ultrahigh Curie temperature(659℃)are gotten in Bi_(4)Ti_(3)-x(Mn_(1/3)Nb_(2/3))xO_(12)(BTMN)ceramics,which are among the top values in the BIT-based ceramics.More importantly,the(Mn_(1/3)Nb_(2/3))(4+d)+complex-ion modified Bi_(4)Ti_(3)O_(12)-based ceramics are characterized with excellent piezoelectric stability up to 500℃(d33>30.0 pC/N at 500℃))and significantly reduced conductivity(only~10^(-7)U-1 cm^(-1)at 500℃).Moreover,enhanced ferroelectricity and good dielectric stability were also obtained.The better comprehensive properties can be ascribed to two aspects.First,the concentration of oxygen vacancy defects is obviously reduced,and their distribution is effectively controlled in BITMN ceramics.Second,the introduction of(Mn_(1/3)Nb_(2/3))^((4+δ)+)complex-ion gives rise to the antiphase boundaries and massive ferroelectric domain walls.This works not only reveal the high potential of BITMN ceramics for high-temperature piezoelectric applications but also deepen the understanding of the structure-properties relationship in BIT-based materials.

Synergistic effects of CeO_(2)/Cu_(2)O on CO catalytic oxidation:Electronic interaction and oxygen defect

For CO catalytic oxidation,Cu and Ce species are of great importance,between which the synergistic effect is worth investigating.In this work,CeO_(2)/Cu_(2)O with Cu_(2)O {111} and {100} planes were comparatively explored on CO catalytic oxidation to reveal the effects of interfacial electronic interactions and oxygen defects.The activity result demonstrates that CeO_(2)/o-Cu_(2)O {111} has superior performance compared with CeO_(2)/c-Cu_(2)O {100}.Credit to the coordination unsaturated copper atoms(Cu_(CUS)) on oCu_(2)O {111} surface,the interfacial electronic interactions on CeO_(2)/o-Cu_(2)O {111} are more obvious than those on CeO_(2)/c-Cu_(2)O {100},leading to richer oxygen defect generation,better redox and activation abilities of CO and O_(2) reactants.Furthermore,the reaction mechanism of CeO_(2)/o-Cu_(2)O {111} on CO oxidation is revealed,i.e.,CO and O_(2) are adsorbed on the Cucus on Cu_(2)O {111} and oxygen defect of CeO_(2),respectively,and then synergistically promote the CO oxidation to CO_(2).The work sheds light on the designing optimized ceria and copper-based catalysts and the mechanism of CO oxidation.