Single-atom(SA) catalysts have emerged as a pivotal area drawing extensive research interest due to their high catalytic activities.However,SA catalysts are often plagued by the aggregation and deactivation of SA site...Single-atom(SA) catalysts have emerged as a pivotal area drawing extensive research interest due to their high catalytic activities.However,SA catalysts are often plagued by the aggregation and deactivation of SA sites under reaction conditions.This study focuses on CO oxidation over Gd-doped ceriasupported Cu catalysts and aims to provide a new strategy to stabilize the SA site,in which a Cu SA site is "prestored" in a relatively stable Cu cluster and can be dynamically activated under reaction conditions.Three typical Cu_(10)/CeO_(2)catalyst models were built with different Gd-doping contents,which are pristine Cu_(10)/CeO_(2),Cu_(10)/Gd_(0.125)Ce_(0.875)O_(2),and Cu_(10)/Gd_(0.25)Ce_(0.75)O_(2),respectively.We performed density functional theory(DFT) calculations on the Cu_(10)/Gd-CeO_(2)system to investigate the adsorption of CO and O_(2)molecules,the formation of surface oxygen vacancy(OV) and dynamic Cu SA site,and potential energy surfaces of CO oxidation process.Ab initio thermodynamic analysis suggests that the saturation adsorption of CO on Cu_(10)and high Gd-doping in CeO_(2)lead to a spontaneously formed single Cu-CO site and an OVdefect on ceria surface.The CO oxidation process is identified as a two-paths-coupled catalytic cycle,in which Path Ⅰ is activated by the terminal O atom of adsorbed O_(2)at surface OVsite while Path Ⅱinitiates with the lattice O atom of CeO_(2)surface.The micro kinetic modeling demonstrates that the dominant pathway is Path Ⅰ for the undoped and low-doping cases,and Path Ⅱ for the high-doping case which exhibits a novel mechanism for CO oxidation and the highest reaction activity due to the participation of the dynamic SA site.展开更多
Phase transitions, morphology changes, and oxidation mechanism of the ilmenite oxidation process were investigated. FeTi03 transforms to hematite and rutile when oxidation at 700-800 ℃, and pseudobrookite is formed w...Phase transitions, morphology changes, and oxidation mechanism of the ilmenite oxidation process were investigated. FeTi03 transforms to hematite and rutile when oxidation at 700-800 ℃, and pseudobrookite is formed when the oxidation temperature reaches 900 ℃. The initial ilmenite powder exhibits paramagnetism; however, after being oxidized at the intermediate temperature （800-850 ℃）, the oxidation product exhibits weak ferromagnetism. The oxidation mechanism was discussed. The microstructure observations show that a lot of micro-pores emerge on the surfaces of ilmenite particles at the intermediate temperature, which is deemed to be caoable ofenhancin~ the mass transfer ofoxgen during oxidation.展开更多
Water electrolysis,a process for producing green hydrogen from renewable energy,plays a crucial role in the transition toward a sustainable energy landscape and the realization of the hydrogen economy.Oxygen evolution...Water electrolysis,a process for producing green hydrogen from renewable energy,plays a crucial role in the transition toward a sustainable energy landscape and the realization of the hydrogen economy.Oxygen evolution reaction(OER)is a critical step in water electrolysis and is often limited by its slow kinetics.Two main mechanisms,namely the adsorbate evolution mechanism(AEM)and lattice oxygen oxidation mechanism(LOM),are commonly considered in the context of OER.However,designing efficient catalysts based on either the AEM or the LOM remains a topic of debate,and there is no consensus on whether activity and stability are directly related to a certain mechanism.Considering the above,we discuss the characteristics,advantages,and disadvantages of AEM and LOM.Additionally,we provide insights on leveraging the LOM to develop highly active and stable OER catalysts in future.For instance,it is essential to accurately differentiate between reversible and irreversible lattice oxygen redox reactions to elucidate the LOM.Furthermore,we discuss strategies for effectively activating lattice oxygen to achieve controllable steady-state exchange between lattice oxygen and an electrolyte(OH^(-)or H_(2)O).Additionally,we discuss the use of in situ characterization techniques and theoretical calculations as promising avenues for further elucidating the LOM.展开更多
Resin-bonded Al-SiC composite was sintered at 1100,1300,and 1500℃ in the air,the oxidation mechanism was investigated.The reaction models were also established.The oxidation resistance of the Al-SiC composite was sig...Resin-bonded Al-SiC composite was sintered at 1100,1300,and 1500℃ in the air,the oxidation mechanism was investigated.The reaction models were also established.The oxidation resistance of the Al-SiC composite was significantly enhanced with temperature increase.SiC in the exterior of the composite was partially oxidized slightly,while the transformation of metastable Al_(4)C_(3) to stable Al_(4)SiC_(4) existed in the interior.At 1100℃,Al in the interior reacted with residual C to form Al_(4)C_(3).With increasing to 1300℃,high temperature and low oxygen partial pressure lead to active oxidation of SiC,and internal gas composition transforms to Al_(2)O(g)+CO(g)+SiO(g)as the reaction proceeds.After Al_(4)C_(3) is formed,CO(g)and SiO(g)are continuously deposited on its surface,transforming to Al_(4)SiC_(4).At 1500℃,a dense layer consisting of SiC and Al_(4)SiC_(4) whiskers is formed which cuts off the diffusion channel of oxygen.The active oxidation of SiC is accelerated,enabling more gas to participate in the synthesis of Al_(4)SiC_(4),eventually forming hexagonal lamellar Al_(4)SiC_(4) with mutual accumulation between SiC particles.Introducing Al enhances the oxidation resistance of SiC.In addition,the in situ generated non-oxide is uniformly dispersed on a micro-scale and bonds SiC stably.展开更多
Conventional mechanical machining of a composite material comprising an aluminum matrix reinforced with a high volume fraction of SiC particles(hereinafter referred to as an SiCp/Al composite)faces problems such as ra...Conventional mechanical machining of a composite material comprising an aluminum matrix reinforced with a high volume fraction of SiC particles(hereinafter referred to as an SiCp/Al composite)faces problems such as rapid tool wear,high specific cutting force,and poor surface integrity.Instead,a promising method for solving these problems is laser-induced oxidation-assisted milling(LOAM):under laser irradiation,the local workpiece material reacts with oxygen,thus forming loose and porous oxides that are easily removed.In the present work,the oxidation mechanism of SiCp/Al irradiated by a nanosecond pulsed laser is studied to better understand the laser-induced oxidation behavior and control the characteristics of the oxides,with laser irradiation experiments performed on a 65%SiCp/Al composite with various laser parameters and auxiliary gases(oxygen,nitrogen,and argon).With increasing laser pulse energy density,both the ablated groove depth and the width of the heat-affected zone increase.When oxygen is used as the auxiliary gas,an oxide layer composed of SiO_(2)and Al2O3 forms,and CO_(2)is produced and escapes from the material,thereby forming pores in the oxides.However,when nitrogen or argon is used as the auxiliary gas,a recast layer is produced that is relatively difficult to remove.Under laser irradiation,the sputtered material reacts with oxygen to form oxides on both sides of the ablated groove,and as the laser scanning path advances,the produced oxides accumulate to form an oxide layer.LOAM and conventional milling are compared using the same milling parameters,and LOAM is found to be better for reduced milling force and tool wear and improved machined surface quality.展开更多
In order to better understand the specific substituent effects on the electrochemical oxidation process of β-O-4 bond, a series of methoxyphenyl type β-O-4 dimer model compounds with different localized methoxyl gro...In order to better understand the specific substituent effects on the electrochemical oxidation process of β-O-4 bond, a series of methoxyphenyl type β-O-4 dimer model compounds with different localized methoxyl groups, including 2-(2-methoxyphenoxy)-1-phenylethanone, 2-(2-methoxyphenoxy)-1-phenylethanol, 2-(2-methoxyphenoxy)-1-(4-methoxyphenyl)ethanone, 2-(2-methoxyphenoxy)-1-(4-methoxyphenyl)ethanol, 2-(2,6-dimethoxyphenoxy)-1-(4-methoxyphenyl)ethanone, 2-(2,6-dimethoxyphenoxy)-1-(4-methoxyphenyl)ethanol have been selected and their electrochemical properties have been studied experimentally by cyclic voltammetry, and FT-IR spectroelectrochemistry. Combining with electrolysis products distribution analysis and density functional theory calculations, oxidation mechanisms of all six model dimers have been explored. In particular, a total effect from substituents of both para-methoxy(on the aryl ring closing to Cα) and Cα-OH on the oxidation mechanisms has been clearly observed, showing a significant selectivity on the Cα-Cβbond cleavage induced by electrochemical oxidations.展开更多
ZrCoSb-based half-Heusler(HH)compounds are among the most promising thermoelectric(TE)materials for high-temperature power generation.Oxidation resistance is one of the key issues for realizing the practical applicati...ZrCoSb-based half-Heusler(HH)compounds are among the most promising thermoelectric(TE)materials for high-temperature power generation.Oxidation resistance is one of the key issues for realizing the practical application of TE materials for long-term service in the ambient working environment.In this work,the oxidation behavior of Zr_(0.5)Hf_(0.5)CoSb_(0.8)Sn_(0.2)(ZHCSS)half-Heusler is systematically studied in the service temperature range from 873 to 1073 K.It is revealed that three typical layers of oxidation products tend to form on the surface of HH sample,namely,the dense oxide layer(DOL)composed of(Zr,Hf)O_(2) and CoSb,the alternate oxide layer(AOL)composed of repeated(Zr,Hf)O_(2) and CoSb_(2)O_(6)/Co_(3)O_(4),and the CoSb layer between the DOL and AOL.The mass gain during oxidation is mainly caused by the rapid growth of AOL,which is controlled by the outward diffusion of Zr/Hf and the inward diffusion of oxygen.The formation of a continuous CoSb layer and DOL is found beneficial to block the outward diffusion of Zr/Hf.Based on the analysis of the dominant factors on the outward and inward diffusions as well as the reaction activation energy,a simple approach is proposed to improve the oxidation resistance of Zr_(0.5)Hf_(0.5)CoSb_(0.8)Sn_(0.2)by pre-oxidizing the sample in low oxygen pressure to form the dense(Zr,Hf)O_(2) and CoSb layers as oxidation protecting and/or diffusion blocking layers.The oxidation test shows the effectiveness of such pre-oxidation on the formation and growth of the AOL and therefore on improving the service stability of Zr_(0.5)Hf_(0.5)CoSb_(0.8)Sn_(0.2)at high temperatures in the air.展开更多
High-temperature oxidation is a common failure in high-temperature environments,which widely occur in aircraft engines and aerospace thrusters;as a result,the development of anti-high-temperature oxidation materials h...High-temperature oxidation is a common failure in high-temperature environments,which widely occur in aircraft engines and aerospace thrusters;as a result,the development of anti-high-temperature oxidation materials has been pursued.Ni-based alloys are a common high-temperature material;however,they are too expensive.High-entropy alloys are alternatives for the anti-oxidation property at high temperatures because of their special structure and properties.The recent achievements of high-temperature oxidation are reviewed in this paper.The high-temperature oxidation environment,temperature,phase structure,alloy elements,and preparation methods of high-entropy alloys are summarized.The reason why high-entropy alloys have anti-oxidation ability at high temperatures is illuminated.Current research,material selection,and application prospects of high-temperature oxidation are introduced.展开更多
Different from the oxidation kinetics of other nitrides,the oxide layer on AlN can easily reach tens of micrometers at a temperature above 1200 ℃.In the present study,the oxidation mechanism of AlN is investigated th...Different from the oxidation kinetics of other nitrides,the oxide layer on AlN can easily reach tens of micrometers at a temperature above 1200 ℃.In the present study,the oxidation mechanism of AlN is investigated through microstructure observation.The analysis indicates that the oxide layer is full of small pores.The formation of pores generates additional surface area to induce further reaction.The reaction thus controls the oxidation in the temperature range from 1050 to 1350 ℃.The oxidation rate becomes slow as the oxide layer reaches a critical thickness.展开更多
This work employed an inductively coupled plasma wind tunnel to study the dynamic oxidation mechanisms of carbon fiber reinforced SiC matrix composite(C_(f)/SiC)in high-enthalpy and high-speed plasmas.The results high...This work employed an inductively coupled plasma wind tunnel to study the dynamic oxidation mechanisms of carbon fiber reinforced SiC matrix composite(C_(f)/SiC)in high-enthalpy and high-speed plasmas.The results highlighted a transition of passive/active oxidations of SiC at 800–1600℃and 1–5 kPa.Specially,the active oxidation led to the corrosion of the SiC coating and interruption of the SiO_(2) growth.The transition borders of active/passive oxidations were thus defined with respect to oxidation temperature and partial pressure of atomic O in the high-enthalpy and high-speed plasmas.In the transition and passive domains,the SiC dissipation was negligible.By multiple dynamic oxidations of C_(f)/SiC in the domains,the SiO_(2) thickness was not monotonously increased due to the competing mechanisms of passive oxidation of SiC and dissipation of SiO_(2).In addition,the mechanical properties of the SiC coating/matrix and the C_(f)/SiC were maintained after long-term dynamic oxidations,which suggested an excellent thermal stability of C_(f)/SiC serving in thermal protection systems(TPSs)of reusable hypersonic vehicles.展开更多
Experiments were conducted in a fixed-bed reactor containing a commercial V2O5/WO3/TiO2 catalyst to investigate mercury oxidation in the presence of HCl and O2. Mercury oxidation was improved significantly in the pres...Experiments were conducted in a fixed-bed reactor containing a commercial V2O5/WO3/TiO2 catalyst to investigate mercury oxidation in the presence of HCl and O2. Mercury oxidation was improved significantly in the presence of HCl and O2, and the Hg^0 oxidation efficiencies decreased slowly as the temperature increased from 200 to 400℃. Upon pretreatment with HCl and O2 at 350℃, the catalyst demonstrated higher catalytic activity for Hg^0 oxidation. Notably,the effect of pretreatment with HCl alone was not obvious. For the catalyst treated with HCl and O2, better performance was observed with lower reaction temperatures. The results showed that both HCl and Hg^0 were first adsorbed onto the catalyst and then reacted with O2 following its adsorption, which indicates that the oxidation of Hg^0 over the commercial catalyst followed the Langmuir–Hinshelwood mechanism. Several characterization techniques, including Hg^0temperature-programmed desorption（Hg-TPD） and X-ray photoelectron spectroscopy（XPS）, were employed in this work. Hg-TPD profiles showed that weakly adsorbed mercury species were converted to strongly bound species in the presence of HCl and O2. XPS patterns indicated that new chemisorbed oxygen species were formed by the adsorption of HCl, which consequently facilitated the oxidation of mercury.展开更多
The oxidation of carbon nanotubes, C60 and graphite was studied by thermogravimetric (TG) analysis and differential thermal analysis (DTA) technique, and the oxidation kinetic models of three carbon materials studied ...The oxidation of carbon nanotubes, C60 and graphite was studied by thermogravimetric (TG) analysis and differential thermal analysis (DTA) technique, and the oxidation kinetic models of three carbon materials studied were analyzed by mechanism-function method. The results indicate that three carbon species adopt different oxidation mechanisms due to their different structures. The oxidation of carbon nanotubes with cylindrical structure follows contracting volume reaction mechanism [R3 mechanism, 1- (1- α)^1/3 = kt], indicating that the oxidation of carbon nanotubes takes place from the ends to the center. For graphite with planar sandwich structure, the oxidation starts at the edges initially and gradually moves toward the center, which corresponds to contracting area phase boundary reaction mechanism [R2 mechanism, 1 - (1 - α)^1/2 = kt]. The oxidation of C60 with spherical structure, however, is complex and apparently cannot be illustrated with a single kinetic model. The values of apparent activation energy obtained by the mechanism-function method are (145 ± 5) kJ·mol^-1 for carbon nanotubes and (193 ± 7) kJ·mol^-1 for graphite, respectively, while the value of apparent activation energy for C60 determined using Kissinger method is 91 kJ·mol^-1。展开更多
Transition metal chalcogenides(TMCs)are recognized as pre-catalysts,and their(oxy)hydroxides derived from electrochemical reconstruction are the active species in the water oxidation.However,understanding the role of ...Transition metal chalcogenides(TMCs)are recognized as pre-catalysts,and their(oxy)hydroxides derived from electrochemical reconstruction are the active species in the water oxidation.However,understanding the role of the residual chalcogen in the reconstructed layer is lacking in detail,and the corresponding catalytic mechanism remains controversial.Here,taking Cu_(1-x)Co_(x)S as a platform,we explore the regulating effect and existence form of the residual S doped into the reconstructive layer for oxygen evolution reaction(OER),where a dual-path OER mechanism is proposed.First-principles calculations and operando~(18)O isotopic labeling experiments jointly reveal that the residual S in the reconstructive layer of Cu_(1-x)Co_(x)S can wisely balance the adsorbate evolution mechanism(AEM)and lattice oxygen oxidation mechanism(LOM)by activating lattice oxygen and optimizing the adsorption/desorption behaviors at metal active sites,rather than change the reaction mechanism from AEM to LOM.Following such a dual-path OER mechanism,Cu_(0.4)Co_(0.6)S-derived Cu_(0.4)Co_(0.6)OSH not only overcomes the restriction of linear scaling relationship in AEM,but also avoids the structural collapse caused by lattice oxygen migration in LOM,so as to greatly reduce the OER potential and improved stability.展开更多
The oxidation behavior of ferrovanadium spinel(FeV_(2)O_(4)),synthesized via high-temperature solid-state reaction,was investigated using thermogravimetry,X-ray diffractometry,and X-ray photoelectron spectroscopy over...The oxidation behavior of ferrovanadium spinel(FeV_(2)O_(4)),synthesized via high-temperature solid-state reaction,was investigated using thermogravimetry,X-ray diffractometry,and X-ray photoelectron spectroscopy over the temperature range of 450–700℃.The results revealed that the oxidation process of FeV_(2)O_(4)can be divided into three stages with the second stage being responsible for maximum weight gain due to oxidation.Three classical methods were employed to analyze the reaction mechanisms and model functions for distinct oxidation stages.The random nucleation and subsequent growth(A_(3))kinetic model was found to be applicable to both initial and secondary stage.The third stage of oxidation was consistent with the three-dimensional diffusion,spherical symmetry(D_(3))kinetic mode.Both the model-function method and the model-free method were utilized to investigate the apparent activation energy of the oxidation reaction at each stage.It was found that the intermediates including Fe_(3)O_(4),VO_(2),V_(2)O_(3),and Fe_(2.5)V_(7.11)O_(16),played significant roles in the oxidation process prior to the final formation of FeVO_(4)and V_(2)O_(5)through oxidation of FeV_(2)O_(4).展开更多
The oxidation behavior of 316L austenitic steel after thermal aging process at 600℃for 6 h was investigated in the supercritical water(600℃/25 MPa)with 1000 h.Results showed that the grain size and the proportion of...The oxidation behavior of 316L austenitic steel after thermal aging process at 600℃for 6 h was investigated in the supercritical water(600℃/25 MPa)with 1000 h.Results showed that the grain size and the proportion of high angle grain boundaries(HAGB)increased in the steel after thermal aging process,with the observation of micro-textures.The weight gain rate of the steel after aging process increased,presenting the decreased Cr_(2)O_(3)contain in the oxide layer,which resulted in the increasing diffusion rate of Fe and O ions in oxide layer.The molecular dynamics simulation results confirmed the high oxidation rate in HAGB and micro-textures for the 316L steel after aging process.展开更多
The composite photoanodes composed by cobalt phosphate catalyst(Co-Pi) modified semiconductor have been widely used for solar water splitting,but the improvement mechanism has not been experimentally confirmed.Here we...The composite photoanodes composed by cobalt phosphate catalyst(Co-Pi) modified semiconductor have been widely used for solar water splitting,but the improvement mechanism has not been experimentally confirmed.Here we use transient photoelectrochemical measurements and impedance spectroscopy to investigate the effect of Co-Pi catalyst on hematite nanowire photoanode.It is found that under illumination the Co-Pi catalyst can efficiently promote the transfer of photo-generated holes to the Co-Pi layer by increasing the electrical conductivity of the composite structure under a low potential.The Co-Pi catalyst can recombine with photo-generated electrons to reduce the surface recombination efficiency of photo-generated holes and electrons under a high potential.These results provide important new understanding of the performance improvement mechanism for the Co-Pi-modified semiconductor nanowire composite photoanodes.展开更多
The vermicular graphite iron is an important material with excellent combination properties for cylinder heads of diesel engines,and the high-temperature oxidation is a crucial problem during service of the component....The vermicular graphite iron is an important material with excellent combination properties for cylinder heads of diesel engines,and the high-temperature oxidation is a crucial problem during service of the component.In this study,the oxidation experiment of RuT400 vermicular graphite iron was performed at 500 ℃,and the oxidation time was chosen as 100 h,200 h,300 h,400 h,and 500 h,respectively.Meanwhile,the corresponding microstructure evolution,oxidation kinetics,and oxidation mechanism were discussed.It is found that oxidation pores and oxide layer often appear at the vermicular graphite on the specimen surface;the vermicular graphite plays the role of oxidation channel,and it tends to diff use along the adjacent pearlite and then connect with each other to form oxidation bridges as the oxidation time prolongs.A linear relationship between oxidation weight gain and the thickness of the oxide layer was established and verifi ed well.These results will give a more comprehensive understanding on the oxidation mechanism of vermicular graphite iron and provide certain guidance for design and preparation of anti-oxidation cast irons.展开更多
Vanadium nitride(VN)is a promising pseudocapacitive material due to the high theoretical capacity,rapid redox Faradaic kinetics,and appropriate potential window.Although VN shows large pseudocapacitance in alkaline el...Vanadium nitride(VN)is a promising pseudocapacitive material due to the high theoretical capacity,rapid redox Faradaic kinetics,and appropriate potential window.Although VN shows large pseudocapacitance in alkaline electrolytes,the electrochemical instability and capacity degradation of VN electrode materials present significant challenges for practical applications.Herein,the capacitance decay mechanism of VN is investigated and a simple strategy to improve cycling stability of VN supercapacitor electrodes is proposed by introducing VO_(4)^(3-)anion in KOH electrolytes.Our results show that the VN electrode is electrochemical stabilization between-1.0and-0.4 V(vs.Hg/Hg O reference electrode)in 1.0 MKOH electrolyte,but demonstrates irreversible oxidation and fast capacitance decay in the potential range of-0.4 to0 V.In situ electrochemical measurements reveal that the capacitance decay of VN from-0.4 to 0 V is ascribed to the irreversible oxidation of vanadium(V)of N–V–O species by oxygen(O)of OH^(-).The as-generated oxidization species are subsequently dissolved into KOH electrolytes,thereby undermining the electrochemical stability of VN.However,this irreversible oxidation process could be hindered by introducing VO_(4)^(3-)in KOH electrolytes.A high volumetric specific capacitance of671.9 F.cm^(-3)(1 A.cm^(-3))and excellent cycling stability(120.3%over 1000 cycles)are achieved for VN nanorod electrode in KOH electrolytes containing VO_(4)^(3-).This study not only elucidates the failure mechanism of VN supercapacitor electrodes in alkaline electrolytes,but also provides new insights into enhancing pseudocapacitive energy storage of VN-based electrode materials.展开更多
The oxygen evolution reaction(OER)serves as a fundamental half–reaction in the electrolysis of water for hydrogen production,which is restricted by the sluggish OER reaction kinetics and unable to be practically appl...The oxygen evolution reaction(OER)serves as a fundamental half–reaction in the electrolysis of water for hydrogen production,which is restricted by the sluggish OER reaction kinetics and unable to be practically applied.The traditional lattice oxygen oxidation mechanism(LOM)offers an advantageous route by circumventing the formation of M-OOH^(*)in the adsorption evolution mechanism(AEM),thus enhancing the reaction kinetics of the OER but resulting in possible structural destabilization due to the decreased M–O bond order.Fortunately,the asymmetry of tetrahedral and octahedral sites in transition metal spinel oxides permits the existence of non-bonding oxygen,which could be activated by rational band structure design for direct O-O coupling,where the M–O bond maintains its initial bond order.Here,non-bonding oxygen was introduced into NiFe_(2)O_(4)via annealing in an oxygen-deficient atmosphere.Then,in-situ grown sulfate species on octahedral nickel sites significantly improved the reactivity of the non-bonding oxygen electrons,thereby facilitating the transformation of the redox center from metal to oxygen.LOM based on non-bonding oxygen(LOMNB)was successfully activated within NiFe_(2)O_(4),exhibiting a low overpotential of 206 mV to achieve a current density of 10 mA cm^(-2)and excellent durability of stable operation for over 150 h.Additionally,catalysts featuring varying band structures were synthesized for comparative analysis,and it was found that the reversible redox processes of non-bonding oxygen and the accumulation of non-bonding oxygen species containing 2p holes are critical prerequisites for triggering and sustaining the LOMNB pathway in transition metal spinel oxides.These findings may provide valuable insights for the future development of spinel-oxide-based LOM catalysts.展开更多
Ni-La2O3/CeO2 composite films were prepared by electrodeposition from a nickel sulfate bath containing certain content of micrometer and nanometer La2O3/CeO2 particles. The effect of La2O3 or CeO2 particle size on the...Ni-La2O3/CeO2 composite films were prepared by electrodeposition from a nickel sulfate bath containing certain content of micrometer and nanometer La2O3/CeO2 particles. The effect of La2O3 or CeO2 particle size on the oxidation resistance of the electrodeposited Ni-La2O3/CeO2 composites in air at 1000 °C was studied. The results indicate that, compared with the electrodeposited Ni-film, Ni-La2O3/CeO2 composites exhibit a superior oxidation resistance due to the codeposited La2O3 or CeO2 particles blocking the outward diffusion of nickel. Moreover, compared with nanoparticles, La2O3 or CeO2 microparticles have stronger effect because La2O3 or CeO2 microparticles also act as a diffusion barrier layer at the onset of oxidation.展开更多
基金Project supported by State Key Laboratory of Molecular&Process Engineering (RIPP, SINOPEC)(36800000-23-ZC0699-0042)the National Natural Science Foundation of China (22072182, 21776315, 12104513)+2 种基金the National Key Research and Development Program of China (2019YFA0708703)the Taishan Scholars Program of Shandong Province (tsqn201909071)the Shandong Provincial Natural Science Foundation of China (ZR2020QA050, ZR2023MB034)。
文摘Single-atom(SA) catalysts have emerged as a pivotal area drawing extensive research interest due to their high catalytic activities.However,SA catalysts are often plagued by the aggregation and deactivation of SA sites under reaction conditions.This study focuses on CO oxidation over Gd-doped ceriasupported Cu catalysts and aims to provide a new strategy to stabilize the SA site,in which a Cu SA site is "prestored" in a relatively stable Cu cluster and can be dynamically activated under reaction conditions.Three typical Cu_(10)/CeO_(2)catalyst models were built with different Gd-doping contents,which are pristine Cu_(10)/CeO_(2),Cu_(10)/Gd_(0.125)Ce_(0.875)O_(2),and Cu_(10)/Gd_(0.25)Ce_(0.75)O_(2),respectively.We performed density functional theory(DFT) calculations on the Cu_(10)/Gd-CeO_(2)system to investigate the adsorption of CO and O_(2)molecules,the formation of surface oxygen vacancy(OV) and dynamic Cu SA site,and potential energy surfaces of CO oxidation process.Ab initio thermodynamic analysis suggests that the saturation adsorption of CO on Cu_(10)and high Gd-doping in CeO_(2)lead to a spontaneously formed single Cu-CO site and an OVdefect on ceria surface.The CO oxidation process is identified as a two-paths-coupled catalytic cycle,in which Path Ⅰ is activated by the terminal O atom of adsorbed O_(2)at surface OVsite while Path Ⅱinitiates with the lattice O atom of CeO_(2)surface.The micro kinetic modeling demonstrates that the dominant pathway is Path Ⅰ for the undoped and low-doping cases,and Path Ⅱ for the high-doping case which exhibits a novel mechanism for CO oxidation and the highest reaction activity due to the participation of the dynamic SA site.
基金Project(51074105) supported by the National Natural Science Foundation of ChinaProject(51225401) supported by the China National Funds for Distinguished Young Scientists
文摘Phase transitions, morphology changes, and oxidation mechanism of the ilmenite oxidation process were investigated. FeTi03 transforms to hematite and rutile when oxidation at 700-800 ℃, and pseudobrookite is formed when the oxidation temperature reaches 900 ℃. The initial ilmenite powder exhibits paramagnetism; however, after being oxidized at the intermediate temperature （800-850 ℃）, the oxidation product exhibits weak ferromagnetism. The oxidation mechanism was discussed. The microstructure observations show that a lot of micro-pores emerge on the surfaces of ilmenite particles at the intermediate temperature, which is deemed to be caoable ofenhancin~ the mass transfer ofoxgen during oxidation.
基金the support from the National Key R&D Program of China(2020YFA0710000)the National Natural Science Foundation of China(Nos.22008170,22278307,22222808,21978200)+1 种基金the Haihe Laboratory of Sustainable Chemical Transformationsthe Tianjin Research Innovation Project for Postgraduate Students(2022B KYZ035)。
文摘Water electrolysis,a process for producing green hydrogen from renewable energy,plays a crucial role in the transition toward a sustainable energy landscape and the realization of the hydrogen economy.Oxygen evolution reaction(OER)is a critical step in water electrolysis and is often limited by its slow kinetics.Two main mechanisms,namely the adsorbate evolution mechanism(AEM)and lattice oxygen oxidation mechanism(LOM),are commonly considered in the context of OER.However,designing efficient catalysts based on either the AEM or the LOM remains a topic of debate,and there is no consensus on whether activity and stability are directly related to a certain mechanism.Considering the above,we discuss the characteristics,advantages,and disadvantages of AEM and LOM.Additionally,we provide insights on leveraging the LOM to develop highly active and stable OER catalysts in future.For instance,it is essential to accurately differentiate between reversible and irreversible lattice oxygen redox reactions to elucidate the LOM.Furthermore,we discuss strategies for effectively activating lattice oxygen to achieve controllable steady-state exchange between lattice oxygen and an electrolyte(OH^(-)or H_(2)O).Additionally,we discuss the use of in situ characterization techniques and theoretical calculations as promising avenues for further elucidating the LOM.
基金supported by the National Key Research and Development Program of China(No.2021YFB3701400).
文摘Resin-bonded Al-SiC composite was sintered at 1100,1300,and 1500℃ in the air,the oxidation mechanism was investigated.The reaction models were also established.The oxidation resistance of the Al-SiC composite was significantly enhanced with temperature increase.SiC in the exterior of the composite was partially oxidized slightly,while the transformation of metastable Al_(4)C_(3) to stable Al_(4)SiC_(4) existed in the interior.At 1100℃,Al in the interior reacted with residual C to form Al_(4)C_(3).With increasing to 1300℃,high temperature and low oxygen partial pressure lead to active oxidation of SiC,and internal gas composition transforms to Al_(2)O(g)+CO(g)+SiO(g)as the reaction proceeds.After Al_(4)C_(3) is formed,CO(g)and SiO(g)are continuously deposited on its surface,transforming to Al_(4)SiC_(4).At 1500℃,a dense layer consisting of SiC and Al_(4)SiC_(4) whiskers is formed which cuts off the diffusion channel of oxygen.The active oxidation of SiC is accelerated,enabling more gas to participate in the synthesis of Al_(4)SiC_(4),eventually forming hexagonal lamellar Al_(4)SiC_(4) with mutual accumulation between SiC particles.Introducing Al enhances the oxidation resistance of SiC.In addition,the in situ generated non-oxide is uniformly dispersed on a micro-scale and bonds SiC stably.
基金supported by the Fundamental Research Funds for the Central Universities(Grant No.NT2021020)。
文摘Conventional mechanical machining of a composite material comprising an aluminum matrix reinforced with a high volume fraction of SiC particles(hereinafter referred to as an SiCp/Al composite)faces problems such as rapid tool wear,high specific cutting force,and poor surface integrity.Instead,a promising method for solving these problems is laser-induced oxidation-assisted milling(LOAM):under laser irradiation,the local workpiece material reacts with oxygen,thus forming loose and porous oxides that are easily removed.In the present work,the oxidation mechanism of SiCp/Al irradiated by a nanosecond pulsed laser is studied to better understand the laser-induced oxidation behavior and control the characteristics of the oxides,with laser irradiation experiments performed on a 65%SiCp/Al composite with various laser parameters and auxiliary gases(oxygen,nitrogen,and argon).With increasing laser pulse energy density,both the ablated groove depth and the width of the heat-affected zone increase.When oxygen is used as the auxiliary gas,an oxide layer composed of SiO_(2)and Al2O3 forms,and CO_(2)is produced and escapes from the material,thereby forming pores in the oxides.However,when nitrogen or argon is used as the auxiliary gas,a recast layer is produced that is relatively difficult to remove.Under laser irradiation,the sputtered material reacts with oxygen to form oxides on both sides of the ablated groove,and as the laser scanning path advances,the produced oxides accumulate to form an oxide layer.LOAM and conventional milling are compared using the same milling parameters,and LOAM is found to be better for reduced milling force and tool wear and improved machined surface quality.
基金The authors gratefully acknowledge the financial support of the Natural Science Foundation of China,China(Grant No.21975082 and 21736003)the Guangdong Basic and Applied Basic Research Foundation(Grant Number:2019A1515011472 and 2022A1515011341)the Science and Technology Program of Guangzhou(Grant Number:202102080479).
文摘In order to better understand the specific substituent effects on the electrochemical oxidation process of β-O-4 bond, a series of methoxyphenyl type β-O-4 dimer model compounds with different localized methoxyl groups, including 2-(2-methoxyphenoxy)-1-phenylethanone, 2-(2-methoxyphenoxy)-1-phenylethanol, 2-(2-methoxyphenoxy)-1-(4-methoxyphenyl)ethanone, 2-(2-methoxyphenoxy)-1-(4-methoxyphenyl)ethanol, 2-(2,6-dimethoxyphenoxy)-1-(4-methoxyphenyl)ethanone, 2-(2,6-dimethoxyphenoxy)-1-(4-methoxyphenyl)ethanol have been selected and their electrochemical properties have been studied experimentally by cyclic voltammetry, and FT-IR spectroelectrochemistry. Combining with electrolysis products distribution analysis and density functional theory calculations, oxidation mechanisms of all six model dimers have been explored. In particular, a total effect from substituents of both para-methoxy(on the aryl ring closing to Cα) and Cα-OH on the oxidation mechanisms has been clearly observed, showing a significant selectivity on the Cα-Cβbond cleavage induced by electrochemical oxidations.
基金financially supported by the National Key Research and Development Program of China(Grant No.2019YFE0103500)the National Nature Science Foundation of China(NSFC)(Grant Nos.U2141208 and 52102330)+1 种基金and the In-ternational Partnership Program of Chinese Academy of Sciences(Grant No.121631KYSB20200012)the support from CAS Key Technology Talent Program.
文摘ZrCoSb-based half-Heusler(HH)compounds are among the most promising thermoelectric(TE)materials for high-temperature power generation.Oxidation resistance is one of the key issues for realizing the practical application of TE materials for long-term service in the ambient working environment.In this work,the oxidation behavior of Zr_(0.5)Hf_(0.5)CoSb_(0.8)Sn_(0.2)(ZHCSS)half-Heusler is systematically studied in the service temperature range from 873 to 1073 K.It is revealed that three typical layers of oxidation products tend to form on the surface of HH sample,namely,the dense oxide layer(DOL)composed of(Zr,Hf)O_(2) and CoSb,the alternate oxide layer(AOL)composed of repeated(Zr,Hf)O_(2) and CoSb_(2)O_(6)/Co_(3)O_(4),and the CoSb layer between the DOL and AOL.The mass gain during oxidation is mainly caused by the rapid growth of AOL,which is controlled by the outward diffusion of Zr/Hf and the inward diffusion of oxygen.The formation of a continuous CoSb layer and DOL is found beneficial to block the outward diffusion of Zr/Hf.Based on the analysis of the dominant factors on the outward and inward diffusions as well as the reaction activation energy,a simple approach is proposed to improve the oxidation resistance of Zr_(0.5)Hf_(0.5)CoSb_(0.8)Sn_(0.2)by pre-oxidizing the sample in low oxygen pressure to form the dense(Zr,Hf)O_(2) and CoSb layers as oxidation protecting and/or diffusion blocking layers.The oxidation test shows the effectiveness of such pre-oxidation on the formation and growth of the AOL and therefore on improving the service stability of Zr_(0.5)Hf_(0.5)CoSb_(0.8)Sn_(0.2)at high temperatures in the air.
基金This work was financially supported by the National Natural Science Foundation of China(No.52071014)the Fundamental Research Funds for the Central Universities(No.FRF-GF-19-033BZ)the National Key Research and Development Program of China(No.2020YFB0704501).
文摘High-temperature oxidation is a common failure in high-temperature environments,which widely occur in aircraft engines and aerospace thrusters;as a result,the development of anti-high-temperature oxidation materials has been pursued.Ni-based alloys are a common high-temperature material;however,they are too expensive.High-entropy alloys are alternatives for the anti-oxidation property at high temperatures because of their special structure and properties.The recent achievements of high-temperature oxidation are reviewed in this paper.The high-temperature oxidation environment,temperature,phase structure,alloy elements,and preparation methods of high-entropy alloys are summarized.The reason why high-entropy alloys have anti-oxidation ability at high temperatures is illuminated.Current research,material selection,and application prospects of high-temperature oxidation are introduced.
文摘Different from the oxidation kinetics of other nitrides,the oxide layer on AlN can easily reach tens of micrometers at a temperature above 1200 ℃.In the present study,the oxidation mechanism of AlN is investigated through microstructure observation.The analysis indicates that the oxide layer is full of small pores.The formation of pores generates additional surface area to induce further reaction.The reaction thus controls the oxidation in the temperature range from 1050 to 1350 ℃.The oxidation rate becomes slow as the oxide layer reaches a critical thickness.
基金This work was supported by the National Natural Science Foundation of China(Nos.11902333 and 51972027)the CARDC Fundamental and Frontier Technology Research Fund.
文摘This work employed an inductively coupled plasma wind tunnel to study the dynamic oxidation mechanisms of carbon fiber reinforced SiC matrix composite(C_(f)/SiC)in high-enthalpy and high-speed plasmas.The results highlighted a transition of passive/active oxidations of SiC at 800–1600℃and 1–5 kPa.Specially,the active oxidation led to the corrosion of the SiC coating and interruption of the SiO_(2) growth.The transition borders of active/passive oxidations were thus defined with respect to oxidation temperature and partial pressure of atomic O in the high-enthalpy and high-speed plasmas.In the transition and passive domains,the SiC dissipation was negligible.By multiple dynamic oxidations of C_(f)/SiC in the domains,the SiO_(2) thickness was not monotonously increased due to the competing mechanisms of passive oxidation of SiC and dissipation of SiO_(2).In addition,the mechanical properties of the SiC coating/matrix and the C_(f)/SiC were maintained after long-term dynamic oxidations,which suggested an excellent thermal stability of C_(f)/SiC serving in thermal protection systems(TPSs)of reusable hypersonic vehicles.
基金supported by the National Basic Research Program(973)of China(No.2013CB430005)the Special Research Funding for Public Benefit Industries from National Ministry of Environmental Protection(No.201309018)the National Hi-Tech Research and Development Program(863)of China(No.2013AA065404)
文摘Experiments were conducted in a fixed-bed reactor containing a commercial V2O5/WO3/TiO2 catalyst to investigate mercury oxidation in the presence of HCl and O2. Mercury oxidation was improved significantly in the presence of HCl and O2, and the Hg^0 oxidation efficiencies decreased slowly as the temperature increased from 200 to 400℃. Upon pretreatment with HCl and O2 at 350℃, the catalyst demonstrated higher catalytic activity for Hg^0 oxidation. Notably,the effect of pretreatment with HCl alone was not obvious. For the catalyst treated with HCl and O2, better performance was observed with lower reaction temperatures. The results showed that both HCl and Hg^0 were first adsorbed onto the catalyst and then reacted with O2 following its adsorption, which indicates that the oxidation of Hg^0 over the commercial catalyst followed the Langmuir–Hinshelwood mechanism. Several characterization techniques, including Hg^0temperature-programmed desorption（Hg-TPD） and X-ray photoelectron spectroscopy（XPS）, were employed in this work. Hg-TPD profiles showed that weakly adsorbed mercury species were converted to strongly bound species in the presence of HCl and O2. XPS patterns indicated that new chemisorbed oxygen species were formed by the adsorption of HCl, which consequently facilitated the oxidation of mercury.
基金Supported by the Natural Science Foundation of Zhejiang Province (No. 500105).
文摘The oxidation of carbon nanotubes, C60 and graphite was studied by thermogravimetric (TG) analysis and differential thermal analysis (DTA) technique, and the oxidation kinetic models of three carbon materials studied were analyzed by mechanism-function method. The results indicate that three carbon species adopt different oxidation mechanisms due to their different structures. The oxidation of carbon nanotubes with cylindrical structure follows contracting volume reaction mechanism [R3 mechanism, 1- (1- α)^1/3 = kt], indicating that the oxidation of carbon nanotubes takes place from the ends to the center. For graphite with planar sandwich structure, the oxidation starts at the edges initially and gradually moves toward the center, which corresponds to contracting area phase boundary reaction mechanism [R2 mechanism, 1 - (1 - α)^1/2 = kt]. The oxidation of C60 with spherical structure, however, is complex and apparently cannot be illustrated with a single kinetic model. The values of apparent activation energy obtained by the mechanism-function method are (145 ± 5) kJ·mol^-1 for carbon nanotubes and (193 ± 7) kJ·mol^-1 for graphite, respectively, while the value of apparent activation energy for C60 determined using Kissinger method is 91 kJ·mol^-1。
基金supported by the Science and Technology Research Program of Chongqing Municipal Education Commission(KJQN202200550)the Natural Science Foundation Joint Fund for Innovation and Development of Chongqing Municipal Education Commission(CSTB2022NSCQ-LZX0077)+4 种基金the National Natural Science Foundation of China(No.52100065)the Science and Technology Research Program of Natural Science Foundation of Chongqing(cstc2021ycjh-bgzxm0037)the Science and Technology Research Program of Chongqing Municipal Education Commission(KJZD-M202200503)the Chongqing Innovation Research Group Project(No.CXQT21015)the Doctor Start/Talent Introduction Program of Chongqing Normal University(No.02060404/2020009000321)。
文摘Transition metal chalcogenides(TMCs)are recognized as pre-catalysts,and their(oxy)hydroxides derived from electrochemical reconstruction are the active species in the water oxidation.However,understanding the role of the residual chalcogen in the reconstructed layer is lacking in detail,and the corresponding catalytic mechanism remains controversial.Here,taking Cu_(1-x)Co_(x)S as a platform,we explore the regulating effect and existence form of the residual S doped into the reconstructive layer for oxygen evolution reaction(OER),where a dual-path OER mechanism is proposed.First-principles calculations and operando~(18)O isotopic labeling experiments jointly reveal that the residual S in the reconstructive layer of Cu_(1-x)Co_(x)S can wisely balance the adsorbate evolution mechanism(AEM)and lattice oxygen oxidation mechanism(LOM)by activating lattice oxygen and optimizing the adsorption/desorption behaviors at metal active sites,rather than change the reaction mechanism from AEM to LOM.Following such a dual-path OER mechanism,Cu_(0.4)Co_(0.6)S-derived Cu_(0.4)Co_(0.6)OSH not only overcomes the restriction of linear scaling relationship in AEM,but also avoids the structural collapse caused by lattice oxygen migration in LOM,so as to greatly reduce the OER potential and improved stability.
基金Project(cstb2022nscq-msx0801)supported by the Natural Science Foundation of Chongqing,ChinaProject(52004044)supported by the National Natural Science Foundation of China+2 种基金Project(ckrc2022030)supported by the Foundation of Chongqing University of Science and Technology,ChinaProject(YKJCX2220216)supported by the Graduate Research Innovation Project of Chongqing University of Science and Technology,ChinaProject(202311551007)supported by the National Undergraduate Training Program for Innovation and Entrepreneurship,China。
文摘The oxidation behavior of ferrovanadium spinel(FeV_(2)O_(4)),synthesized via high-temperature solid-state reaction,was investigated using thermogravimetry,X-ray diffractometry,and X-ray photoelectron spectroscopy over the temperature range of 450–700℃.The results revealed that the oxidation process of FeV_(2)O_(4)can be divided into three stages with the second stage being responsible for maximum weight gain due to oxidation.Three classical methods were employed to analyze the reaction mechanisms and model functions for distinct oxidation stages.The random nucleation and subsequent growth(A_(3))kinetic model was found to be applicable to both initial and secondary stage.The third stage of oxidation was consistent with the three-dimensional diffusion,spherical symmetry(D_(3))kinetic mode.Both the model-function method and the model-free method were utilized to investigate the apparent activation energy of the oxidation reaction at each stage.It was found that the intermediates including Fe_(3)O_(4),VO_(2),V_(2)O_(3),and Fe_(2.5)V_(7.11)O_(16),played significant roles in the oxidation process prior to the final formation of FeVO_(4)and V_(2)O_(5)through oxidation of FeV_(2)O_(4).
基金supported by the Hebei Natural Science Foundation(E2023502105)the China Postdoctoral Science Foundation(2023M741155)the Fundamental Research Funds for the Central Universities(JB2023030).
文摘The oxidation behavior of 316L austenitic steel after thermal aging process at 600℃for 6 h was investigated in the supercritical water(600℃/25 MPa)with 1000 h.Results showed that the grain size and the proportion of high angle grain boundaries(HAGB)increased in the steel after thermal aging process,with the observation of micro-textures.The weight gain rate of the steel after aging process increased,presenting the decreased Cr_(2)O_(3)contain in the oxide layer,which resulted in the increasing diffusion rate of Fe and O ions in oxide layer.The molecular dynamics simulation results confirmed the high oxidation rate in HAGB and micro-textures for the 316L steel after aging process.
基金financially supported by the National Natural Science Foundation of China (No.21503109)the Research-Starting Funds for Introduced Talents of Nanjing Tech University。
文摘The composite photoanodes composed by cobalt phosphate catalyst(Co-Pi) modified semiconductor have been widely used for solar water splitting,but the improvement mechanism has not been experimentally confirmed.Here we use transient photoelectrochemical measurements and impedance spectroscopy to investigate the effect of Co-Pi catalyst on hematite nanowire photoanode.It is found that under illumination the Co-Pi catalyst can efficiently promote the transfer of photo-generated holes to the Co-Pi layer by increasing the electrical conductivity of the composite structure under a low potential.The Co-Pi catalyst can recombine with photo-generated electrons to reduce the surface recombination efficiency of photo-generated holes and electrons under a high potential.These results provide important new understanding of the performance improvement mechanism for the Co-Pi-modified semiconductor nanowire composite photoanodes.
基金the National Natural Science Foundation of China (NSFC) under Grant.No.51871224the Natural Science Foundation of Liaoning Province under Grant.No.20180550880。
文摘The vermicular graphite iron is an important material with excellent combination properties for cylinder heads of diesel engines,and the high-temperature oxidation is a crucial problem during service of the component.In this study,the oxidation experiment of RuT400 vermicular graphite iron was performed at 500 ℃,and the oxidation time was chosen as 100 h,200 h,300 h,400 h,and 500 h,respectively.Meanwhile,the corresponding microstructure evolution,oxidation kinetics,and oxidation mechanism were discussed.It is found that oxidation pores and oxide layer often appear at the vermicular graphite on the specimen surface;the vermicular graphite plays the role of oxidation channel,and it tends to diff use along the adjacent pearlite and then connect with each other to form oxidation bridges as the oxidation time prolongs.A linear relationship between oxidation weight gain and the thickness of the oxide layer was established and verifi ed well.These results will give a more comprehensive understanding on the oxidation mechanism of vermicular graphite iron and provide certain guidance for design and preparation of anti-oxidation cast irons.
基金financially supported by the National Natural Science Foundation of China(No.U2004210)Application Foundation Frontier Project of Wuhan Science and Technology Program(No.2020010601012199)City University of Hong Kong Strategic Research Grant,Hong Kong,China(No.7005505)。
文摘Vanadium nitride(VN)is a promising pseudocapacitive material due to the high theoretical capacity,rapid redox Faradaic kinetics,and appropriate potential window.Although VN shows large pseudocapacitance in alkaline electrolytes,the electrochemical instability and capacity degradation of VN electrode materials present significant challenges for practical applications.Herein,the capacitance decay mechanism of VN is investigated and a simple strategy to improve cycling stability of VN supercapacitor electrodes is proposed by introducing VO_(4)^(3-)anion in KOH electrolytes.Our results show that the VN electrode is electrochemical stabilization between-1.0and-0.4 V(vs.Hg/Hg O reference electrode)in 1.0 MKOH electrolyte,but demonstrates irreversible oxidation and fast capacitance decay in the potential range of-0.4 to0 V.In situ electrochemical measurements reveal that the capacitance decay of VN from-0.4 to 0 V is ascribed to the irreversible oxidation of vanadium(V)of N–V–O species by oxygen(O)of OH^(-).The as-generated oxidization species are subsequently dissolved into KOH electrolytes,thereby undermining the electrochemical stability of VN.However,this irreversible oxidation process could be hindered by introducing VO_(4)^(3-)in KOH electrolytes.A high volumetric specific capacitance of671.9 F.cm^(-3)(1 A.cm^(-3))and excellent cycling stability(120.3%over 1000 cycles)are achieved for VN nanorod electrode in KOH electrolytes containing VO_(4)^(3-).This study not only elucidates the failure mechanism of VN supercapacitor electrodes in alkaline electrolytes,but also provides new insights into enhancing pseudocapacitive energy storage of VN-based electrode materials.
文摘The oxygen evolution reaction(OER)serves as a fundamental half–reaction in the electrolysis of water for hydrogen production,which is restricted by the sluggish OER reaction kinetics and unable to be practically applied.The traditional lattice oxygen oxidation mechanism(LOM)offers an advantageous route by circumventing the formation of M-OOH^(*)in the adsorption evolution mechanism(AEM),thus enhancing the reaction kinetics of the OER but resulting in possible structural destabilization due to the decreased M–O bond order.Fortunately,the asymmetry of tetrahedral and octahedral sites in transition metal spinel oxides permits the existence of non-bonding oxygen,which could be activated by rational band structure design for direct O-O coupling,where the M–O bond maintains its initial bond order.Here,non-bonding oxygen was introduced into NiFe_(2)O_(4)via annealing in an oxygen-deficient atmosphere.Then,in-situ grown sulfate species on octahedral nickel sites significantly improved the reactivity of the non-bonding oxygen electrons,thereby facilitating the transformation of the redox center from metal to oxygen.LOM based on non-bonding oxygen(LOMNB)was successfully activated within NiFe_(2)O_(4),exhibiting a low overpotential of 206 mV to achieve a current density of 10 mA cm^(-2)and excellent durability of stable operation for over 150 h.Additionally,catalysts featuring varying band structures were synthesized for comparative analysis,and it was found that the reversible redox processes of non-bonding oxygen and the accumulation of non-bonding oxygen species containing 2p holes are critical prerequisites for triggering and sustaining the LOMNB pathway in transition metal spinel oxides.These findings may provide valuable insights for the future development of spinel-oxide-based LOM catalysts.
基金Project(GC13A113)supported by the Technology Research and Development Program of Heilongjiang Provincial Science and Technology DepartmentProject(12511469)supported by Heilongjiang Provincial Science and Technology Department
文摘Ni-La2O3/CeO2 composite films were prepared by electrodeposition from a nickel sulfate bath containing certain content of micrometer and nanometer La2O3/CeO2 particles. The effect of La2O3 or CeO2 particle size on the oxidation resistance of the electrodeposited Ni-La2O3/CeO2 composites in air at 1000 °C was studied. The results indicate that, compared with the electrodeposited Ni-film, Ni-La2O3/CeO2 composites exhibit a superior oxidation resistance due to the codeposited La2O3 or CeO2 particles blocking the outward diffusion of nickel. Moreover, compared with nanoparticles, La2O3 or CeO2 microparticles have stronger effect because La2O3 or CeO2 microparticles also act as a diffusion barrier layer at the onset of oxidation.
