The rapid development of high-power and pulsed-power techniques inspires extensive investigates on high-performance ceramic-based capacitors.However,the low recoverable energy density(Wrec)hampers their wider applicat...The rapid development of high-power and pulsed-power techniques inspires extensive investigates on high-performance ceramic-based capacitors.However,the low recoverable energy density(Wrec)hampers their wider applications.Herein,the non-stoichiometric Bi_(0.5)Na_(0.5)TiO_(3)-based ceramics were designed and studied.The proper introduction of oxygen vacancies facilitated activating defect dipole,giving rise to reduced remanent polarization.Consequently,the optimal composition exhibited an exceptional high Wrec of 8.3 J/cm^(3),a high efficiency of 85%,and excellent anti-fatigue and thermal reliability.This work provides an efficient approach to explore ceramic capacitors with high capacitive energy storage performances.展开更多
Non-stoichiometric Nd_((1+x))(Mg_(1/2)Sn_(1/2))O_(3)(-0.04=x≤0.04,NMS)ceramics were fabricated via a conventional solid-state reaction method.Crystal structures and morphologies were investigated by Xray diffraction(...Non-stoichiometric Nd_((1+x))(Mg_(1/2)Sn_(1/2))O_(3)(-0.04=x≤0.04,NMS)ceramics were fabricated via a conventional solid-state reaction method.Crystal structures and morphologies were investigated by Xray diffraction(XRD)and scanning electron microscopy(SEM),respectively.The main crystalline phase is monoclinic Nd(Mg_(1/2)Sn_(1/2))O_(3) with a double perovskite structure(P21/n space group)for the NMS system proved by XRD.The sample at x=0.01 has the best crystallinity and evenly distributed crystal grains observed by SEM.The optimum performances(ε_(r)=19.87,Q×f=41840 GHz,f=12.05 GHz)are obtained at x=0.01.Lattice vibrational modes of the Raman spectra were assigned and illustrated,in detail.The dielectric properties obtained by fitting infrared reflectance spectra with the help of four-parameter semi-quantum model are consistent with the calculated values by microscopic polarization and damping coefficients.The reverse translational vibration of the NdeMgO_(6),the F_(5u)^((5)) mode,provides the greatest contribution to the dielectric response.The relationships between crystal structures and dielectric properties were mainly established using lattice vibrational modes as a media.展开更多
Oxidation state changes under reaction conditions are very common in heterogeneous catalysis. However, due to the limitation of experiment and computational methods, the relation between oxidation state and catalytic ...Oxidation state changes under reaction conditions are very common in heterogeneous catalysis. However, due to the limitation of experiment and computational methods, the relation between oxidation state and catalytic activity is not clear. Herein, we obtain the most stable structures of palladium oxide films with different oxidation states on palladium metal surfaces using density functional theory calculations and a state-of-the-art optimization method, namely the particle swarm optimization. These structures clearly show the process of palladium oxide film formation on metallic surfaces. Using CO oxidation as a model reaction, we find that the activities increase first and then decrease with the increase of oxidation states, peaking at Pd_4O_3. Our findings offer an understanding of the phase transformation and the activity of non-stoichiometric phases.展开更多
Energy supply dominated by fossil energy has been and remains the main cause of carbon dioxide emissions,the major greenhouse gas leading to the current grave climate change challenges.Many technical pathways have bee...Energy supply dominated by fossil energy has been and remains the main cause of carbon dioxide emissions,the major greenhouse gas leading to the current grave climate change challenges.Many technical pathways have been proposed to address the challenges.Carbon capture and utilization(CCU) represents one of the approaches and thermochemical CO_(2) splitting driven by thermal energy is a subset of the CCU,which converts the captured CO_(2) into CO and makes it possible to achieve closed-loop carbon recirculation.Redox-active catalysts are among the most critical components of the thermochemical splitting cycles and perovskites are regarded as the most promising catalysts.Here we review the latest advancements in thermochemical cycles based on perovskites,covering thermodynamic principles,material modifications,reaction kinetics,oxygen pressure control,circular strategies,and demonstrations to provide a comprehensive overview of the topical area.Thermochemical cycles based on such materials require the consideration of trade-off between cost and efficiency,which is related to actual material used,operation mode,oxygen removal,and heat recovery.Lots of efforts have been made towards improving reaction rates,conversion efficiency and cycling stability,materials related research has been lacking-a key aspect affecting the performance across all above aspects.Double perovskites and composite perovskites arise recently as a potentially promising addition to material candidates.For such materials,more effective oxygen removal would be needed to enhance the overall efficiency,for which thermochemical or electrochemical oxygen pumps could contribute to efficient oxygen removal as well as serve as means for inert gas regeneration.The integration of thermochemical CO_(2) splitting process with downstream fuel production and other processes could reduce costs and increase efficiency of the technology.This represents one of the directions for the future research.展开更多
The crystal structure, the phase composition and the electrochemical characteristics of Zr0.9Ti0.1(Ni1.1Mn0.7V0.2)x (x=0.90, 0.95, 1.00, 1.05) alloys were investigated by means of XRD, SEM, EDS and electrochemical mea...The crystal structure, the phase composition and the electrochemical characteristics of Zr0.9Ti0.1(Ni1.1Mn0.7V0.2)x (x=0.90, 0.95, 1.00, 1.05) alloys were investigated by means of XRD, SEM, EDS and electrochemical measurements. It was shown that all alloys are multiphase with C15 Laves phase as a main phase along with C14 phase and some secondary phases. And the amounts of the C14 phase and secondary phases in the four alloys increases with decreasing x. The results indicated that the various stoichiometric ratios have great effects on the electrochemical characteristics such as the maximum discharge capacity, discharge rate capability and self-discharge properties etc. for Zr0.9Ti0.1(Ni1.1Mn0.7 V0.2)X (x=0.90, 0.95, 1.00, 1.05) alloys. The hyper-stoichiometric Zr0.9 Ti0.1(N1.1Mn0.7 V0.20)1.05 exhibits the maximum discharge capacity of 332mAh-g-1. The C14 phase and secondary phases seems to improve discharge rate capability of the alloys.展开更多
Non-stoichiometric copper selenide(Cu_(2-x)Se,x=0.18~0.25)nanomaterials have attracted extensive attentions due to their excellent thermoelectric,optoelectronic and photocatalytic performances.However,efficient produc...Non-stoichiometric copper selenide(Cu_(2-x)Se,x=0.18~0.25)nanomaterials have attracted extensive attentions due to their excellent thermoelectric,optoelectronic and photocatalytic performances.However,efficient production of Cu_(2-x)Se nanoparticles(NPs)through a green and convenient way is still hindered by the inevitable non-environmentally friendly operations in common chemical synthesis.Herein,we initially reveal the coexistence of seleninic acid content and elemental selenium(Se)NPs in pulsed laser-generated Se colloidal solution.Consequently,we put forward firstly a closedcycle reaction mode for totally green production of Cu_(1.8)Se NPs to exclude traditional requirements of high temperature and toxic precursors by using Se colloidal solution.In such closed-cycle reaction,seleninic acid works as the initiator to oxidize copper sheet to release cuprous ions which can catalyze the disproportion of Se NPs to form Se O_(3)^(2-)and Se^(2-)ions and further produce Cu_(2-x)Se NPs,and the by-product SeO_(3)^(2-)ions promote subsequent formation of cuprous from the excessive Cu sheet.In experiments,the adequate copper(Cu)sheet was simply dipped into such Se colloidal solution at 70℃,and then the stream of Cu_(1.8)SeNPs could be produced until the exhaustion of selenium source.The conversion rate of Se element reaches to more than 75%when the size of Se NPs in weakly acidic colloidal solution is limited between 1 nm and 50 nm.The laser irradiation duration shows negative correlation with the size of Se NPs and unobvious impact to the p H of the solution which both are essential to the high yield of Cu_(1.8)SeNPs.Before Cu sheet is exhausted,Se colloidal solution can be successively added without influences to the product quality and the Se conversion rate.Such green methodology positively showcases a brand-new and potential strategy for mass production of Cu_(2-x)Se nanomaterials.展开更多
Introduction The surface structure, distribution and strength of the active centers of a catalyst would directly affect its catalytic activity and selectivity. In principle all the techniques and methods which can mod...Introduction The surface structure, distribution and strength of the active centers of a catalyst would directly affect its catalytic activity and selectivity. In principle all the techniques and methods which can modify the surface and body structure of a catalyst, or influence its physicochemical properties can be used to change the activity and selectivity of a practical catalyst.展开更多
Chemical properties of seawater are studied at forced shifting of Fermi level εF? in the band gap of liquid water due to deviation of its composition H2O1−z ( |?z|−13 ) from the stoichiometric one...Chemical properties of seawater are studied at forced shifting of Fermi level εF? in the band gap of liquid water due to deviation of its composition H2O1−z ( |?z|−13 ) from the stoichiometric one ( z = 0 ). It is shown that the hypo-stoichiometric state ( z > 0 ) of seawater emerges when Fermi level is shifted to the local electron level ?εH3O of hydroxonium H3O+ in galvanic cell with the strongly polarized anode and the quasi-equilibrium cathode. Then, each εH3O is occupied by electron and hydroxonium radicals [H3O]? together with hydroxide anions [OH−]?form in seawater hydrated electrons [(H2O)2−] . The opposite hyper-stoichiometric state ( z εOH for removing electron from each hydroxide ion OH−and forming hydroxyl radicals [OH] as strong oxidizers. It turned out that the ions of sodium and chlorine are connected into hydrates of sodium hypochlorite NaClO in this case.展开更多
La_(1-x)CoO_(3-δ)catalysts with different non-stoichiometry of lanthanum ions were synthesized by using the sol-gel method,and their catalytic performance in toluene combustion was investigated.The results showed tha...La_(1-x)CoO_(3-δ)catalysts with different non-stoichiometry of lanthanum ions were synthesized by using the sol-gel method,and their catalytic performance in toluene combustion was investigated.The results showed that the catalytic activity and stability of A-site nonstoichiometric La_(1-x)CoO_(3-δ)were improved to a certain extent compared with pure LaCoO_(3)perovskite.Among them,the La_(0.9)CoO_(3-δ)catalyst gave the best catalytic performance for toluene oxidation.It achieved 90%toluene conversion at 205℃under the conditions of a WHSV(weight hourly space velocity)of 22,500 mL/(g·hr)and a 500 ppmV-toluene concentration.Various characterization techniques were used to investigate the relationship between the structure of these catalysts and their catalytic performance.It was found that the non-stoichiometric modification of the lanthanum ion at position A in LaCoO_(3)changed the surface element state of the catalyst and increased the oxygen vacancy content,thus,combined with improved reducibility,improving toluene degradation on the catalyst.展开更多
The reduction processes of anodic PbO2 films formed on Pb-Sb alloys in 4.5mol·dm-3 H2SO4 solution at 1.4 V(vs.Hg/Hg2SO4) for 1 h have been investigated by pho-tocurrent method,chronoamperometry,linear sweep volta...The reduction processes of anodic PbO2 films formed on Pb-Sb alloys in 4.5mol·dm-3 H2SO4 solution at 1.4 V(vs.Hg/Hg2SO4) for 1 h have been investigated by pho-tocurrent method,chronoamperometry,linear sweep voltammetry as well as X-ray diifractornetry.It was found that the reduction of most of the β-PbO2 and part of the α-PbO2 to PbSO4 can be completed within I s between 0.9 V and 1.0 V(vs.Hg/Hg2SO4) and proceeds much faster than that of the remaining a-PbO2 into photoactive α·PbOx (1<x<1.4).The presence of antimony in the alloy retards significantly the reduction of the remaining a-PbO2 and decreases slightly the band-gap energy of t-PbO.展开更多
基金supported by the National Natural Science Foundation of China(Nos.12004181,52073144)Natural Science Foundation of Jiangsu Province(Nos.BK20200473,BK20201301)the Fundamental Research Funds for the Central Universities(No.30922010309)。
文摘The rapid development of high-power and pulsed-power techniques inspires extensive investigates on high-performance ceramic-based capacitors.However,the low recoverable energy density(Wrec)hampers their wider applications.Herein,the non-stoichiometric Bi_(0.5)Na_(0.5)TiO_(3)-based ceramics were designed and studied.The proper introduction of oxygen vacancies facilitated activating defect dipole,giving rise to reduced remanent polarization.Consequently,the optimal composition exhibited an exceptional high Wrec of 8.3 J/cm^(3),a high efficiency of 85%,and excellent anti-fatigue and thermal reliability.This work provides an efficient approach to explore ceramic capacitors with high capacitive energy storage performances.
基金supported by National Natural Science Foundation of China(Grant 11874240)Guangxi Information Materials Key Laboratory Open Research Fund(171007-K)+3 种基金State Key Laboratory of New Ceramic and Fine Processing Tsinghua University(No.KF201811)the Opening Project of Key Laboratory of Inorganic Functional Materials and Devices,Chinese Academy of Sciences(Grant No.KLIFMD201803)the Natural Science Foundation of Shandong Province,China(No.ZR2016EMM21)Scientific Research Foundation of Shandong University of Science and Technology for Recruited Talents(No.2016RCJJ002).
文摘Non-stoichiometric Nd_((1+x))(Mg_(1/2)Sn_(1/2))O_(3)(-0.04=x≤0.04,NMS)ceramics were fabricated via a conventional solid-state reaction method.Crystal structures and morphologies were investigated by Xray diffraction(XRD)and scanning electron microscopy(SEM),respectively.The main crystalline phase is monoclinic Nd(Mg_(1/2)Sn_(1/2))O_(3) with a double perovskite structure(P21/n space group)for the NMS system proved by XRD.The sample at x=0.01 has the best crystallinity and evenly distributed crystal grains observed by SEM.The optimum performances(ε_(r)=19.87,Q×f=41840 GHz,f=12.05 GHz)are obtained at x=0.01.Lattice vibrational modes of the Raman spectra were assigned and illustrated,in detail.The dielectric properties obtained by fitting infrared reflectance spectra with the help of four-parameter semi-quantum model are consistent with the calculated values by microscopic polarization and damping coefficients.The reverse translational vibration of the NdeMgO_(6),the F_(5u)^((5)) mode,provides the greatest contribution to the dielectric response.The relationships between crystal structures and dielectric properties were mainly established using lattice vibrational modes as a media.
基金supported by the National Natural Science Foundation of China (21333003)Queens University Belfast for a Ph.D. studentship
文摘Oxidation state changes under reaction conditions are very common in heterogeneous catalysis. However, due to the limitation of experiment and computational methods, the relation between oxidation state and catalytic activity is not clear. Herein, we obtain the most stable structures of palladium oxide films with different oxidation states on palladium metal surfaces using density functional theory calculations and a state-of-the-art optimization method, namely the particle swarm optimization. These structures clearly show the process of palladium oxide film formation on metallic surfaces. Using CO oxidation as a model reaction, we find that the activities increase first and then decrease with the increase of oxidation states, peaking at Pd_4O_3. Our findings offer an understanding of the phase transformation and the activity of non-stoichiometric phases.
文摘Energy supply dominated by fossil energy has been and remains the main cause of carbon dioxide emissions,the major greenhouse gas leading to the current grave climate change challenges.Many technical pathways have been proposed to address the challenges.Carbon capture and utilization(CCU) represents one of the approaches and thermochemical CO_(2) splitting driven by thermal energy is a subset of the CCU,which converts the captured CO_(2) into CO and makes it possible to achieve closed-loop carbon recirculation.Redox-active catalysts are among the most critical components of the thermochemical splitting cycles and perovskites are regarded as the most promising catalysts.Here we review the latest advancements in thermochemical cycles based on perovskites,covering thermodynamic principles,material modifications,reaction kinetics,oxygen pressure control,circular strategies,and demonstrations to provide a comprehensive overview of the topical area.Thermochemical cycles based on such materials require the consideration of trade-off between cost and efficiency,which is related to actual material used,operation mode,oxygen removal,and heat recovery.Lots of efforts have been made towards improving reaction rates,conversion efficiency and cycling stability,materials related research has been lacking-a key aspect affecting the performance across all above aspects.Double perovskites and composite perovskites arise recently as a potentially promising addition to material candidates.For such materials,more effective oxygen removal would be needed to enhance the overall efficiency,for which thermochemical or electrochemical oxygen pumps could contribute to efficient oxygen removal as well as serve as means for inert gas regeneration.The integration of thermochemical CO_(2) splitting process with downstream fuel production and other processes could reduce costs and increase efficiency of the technology.This represents one of the directions for the future research.
文摘The crystal structure, the phase composition and the electrochemical characteristics of Zr0.9Ti0.1(Ni1.1Mn0.7V0.2)x (x=0.90, 0.95, 1.00, 1.05) alloys were investigated by means of XRD, SEM, EDS and electrochemical measurements. It was shown that all alloys are multiphase with C15 Laves phase as a main phase along with C14 phase and some secondary phases. And the amounts of the C14 phase and secondary phases in the four alloys increases with decreasing x. The results indicated that the various stoichiometric ratios have great effects on the electrochemical characteristics such as the maximum discharge capacity, discharge rate capability and self-discharge properties etc. for Zr0.9Ti0.1(Ni1.1Mn0.7 V0.2)X (x=0.90, 0.95, 1.00, 1.05) alloys. The hyper-stoichiometric Zr0.9 Ti0.1(N1.1Mn0.7 V0.20)1.05 exhibits the maximum discharge capacity of 332mAh-g-1. The C14 phase and secondary phases seems to improve discharge rate capability of the alloys.
基金the Fund from Hefei National Laboratory for Physical Sciences at the Microscale(Grant No.KF2020110)the Natural Science Foundation of Anhui Province,China(Grant No.1908085ME146)+3 种基金the Key Research and Development Plan of Anhui Province,China(Grant No.201904a05020049)the Director Fund of Institute of Solid State Physics,Chinese Academy of Sciences(Grant No.2019DFY01)the National Natural Science Foundation of China(Grant Nos.52071313 and 51971211)the Hefei Institutes of Physical Science,Chinese Academy of Sciences Director’s Fund(Grant Nos.YZJJZX202018 and YZJJ202102)。
文摘Non-stoichiometric copper selenide(Cu_(2-x)Se,x=0.18~0.25)nanomaterials have attracted extensive attentions due to their excellent thermoelectric,optoelectronic and photocatalytic performances.However,efficient production of Cu_(2-x)Se nanoparticles(NPs)through a green and convenient way is still hindered by the inevitable non-environmentally friendly operations in common chemical synthesis.Herein,we initially reveal the coexistence of seleninic acid content and elemental selenium(Se)NPs in pulsed laser-generated Se colloidal solution.Consequently,we put forward firstly a closedcycle reaction mode for totally green production of Cu_(1.8)Se NPs to exclude traditional requirements of high temperature and toxic precursors by using Se colloidal solution.In such closed-cycle reaction,seleninic acid works as the initiator to oxidize copper sheet to release cuprous ions which can catalyze the disproportion of Se NPs to form Se O_(3)^(2-)and Se^(2-)ions and further produce Cu_(2-x)Se NPs,and the by-product SeO_(3)^(2-)ions promote subsequent formation of cuprous from the excessive Cu sheet.In experiments,the adequate copper(Cu)sheet was simply dipped into such Se colloidal solution at 70℃,and then the stream of Cu_(1.8)SeNPs could be produced until the exhaustion of selenium source.The conversion rate of Se element reaches to more than 75%when the size of Se NPs in weakly acidic colloidal solution is limited between 1 nm and 50 nm.The laser irradiation duration shows negative correlation with the size of Se NPs and unobvious impact to the p H of the solution which both are essential to the high yield of Cu_(1.8)SeNPs.Before Cu sheet is exhausted,Se colloidal solution can be successively added without influences to the product quality and the Se conversion rate.Such green methodology positively showcases a brand-new and potential strategy for mass production of Cu_(2-x)Se nanomaterials.
文摘Introduction The surface structure, distribution and strength of the active centers of a catalyst would directly affect its catalytic activity and selectivity. In principle all the techniques and methods which can modify the surface and body structure of a catalyst, or influence its physicochemical properties can be used to change the activity and selectivity of a practical catalyst.
文摘Chemical properties of seawater are studied at forced shifting of Fermi level εF? in the band gap of liquid water due to deviation of its composition H2O1−z ( |?z|−13 ) from the stoichiometric one ( z = 0 ). It is shown that the hypo-stoichiometric state ( z > 0 ) of seawater emerges when Fermi level is shifted to the local electron level ?εH3O of hydroxonium H3O+ in galvanic cell with the strongly polarized anode and the quasi-equilibrium cathode. Then, each εH3O is occupied by electron and hydroxonium radicals [H3O]? together with hydroxide anions [OH−]?form in seawater hydrated electrons [(H2O)2−] . The opposite hyper-stoichiometric state ( z εOH for removing electron from each hydroxide ion OH−and forming hydroxyl radicals [OH] as strong oxidizers. It turned out that the ions of sodium and chlorine are connected into hydrates of sodium hypochlorite NaClO in this case.
基金support from National Key Research and Development Program of China(No.2019YFC1903903)the National Natural Science Foundation of China(No.21876019)+1 种基金Fundamental Research Funds for the Central Universities(No.DUT20RC(4)003)Natural Science Foundation of Liaoning Province(No.2020-BS-056).
文摘La_(1-x)CoO_(3-δ)catalysts with different non-stoichiometry of lanthanum ions were synthesized by using the sol-gel method,and their catalytic performance in toluene combustion was investigated.The results showed that the catalytic activity and stability of A-site nonstoichiometric La_(1-x)CoO_(3-δ)were improved to a certain extent compared with pure LaCoO_(3)perovskite.Among them,the La_(0.9)CoO_(3-δ)catalyst gave the best catalytic performance for toluene oxidation.It achieved 90%toluene conversion at 205℃under the conditions of a WHSV(weight hourly space velocity)of 22,500 mL/(g·hr)and a 500 ppmV-toluene concentration.Various characterization techniques were used to investigate the relationship between the structure of these catalysts and their catalytic performance.It was found that the non-stoichiometric modification of the lanthanum ion at position A in LaCoO_(3)changed the surface element state of the catalyst and increased the oxygen vacancy content,thus,combined with improved reducibility,improving toluene degradation on the catalyst.
基金Project supported by the State Education Commission of China and the National Natural Science Foundation of China.
文摘The reduction processes of anodic PbO2 films formed on Pb-Sb alloys in 4.5mol·dm-3 H2SO4 solution at 1.4 V(vs.Hg/Hg2SO4) for 1 h have been investigated by pho-tocurrent method,chronoamperometry,linear sweep voltammetry as well as X-ray diifractornetry.It was found that the reduction of most of the β-PbO2 and part of the α-PbO2 to PbSO4 can be completed within I s between 0.9 V and 1.0 V(vs.Hg/Hg2SO4) and proceeds much faster than that of the remaining a-PbO2 into photoactive α·PbOx (1<x<1.4).The presence of antimony in the alloy retards significantly the reduction of the remaining a-PbO2 and decreases slightly the band-gap energy of t-PbO.