The direct decomposition of N2O was investigated over a series of magnesium cobaltite catalysts,MgxCo1-xCo2O4(0.0 ≤ x ≤ 1.0) ,which were prepared by the thermal decomposition of stoichiometric amounts of magnesium h...The direct decomposition of N2O was investigated over a series of magnesium cobaltite catalysts,MgxCo1-xCo2O4(0.0 ≤ x ≤ 1.0) ,which were prepared by the thermal decomposition of stoichiometric amounts of magnesium hydroxide and cobalt acetate. The thermal genesis of the different catalysts from their precursors was explored using thermogravimetric analysis,differential thermal analysis,and X-ray diffraction. Texture analysis was carried out using N2 adsorption at -196 °C. We found that all the catalysts that were calcined at 500 °C have a spinel structure. N2O decomposition activity was found to increase with an increase in the spinel structure's magnesium content. The influence of alkali cation promoters(Li,Na,K,and Cs) on the activity of the most active catalyst in the MgxCo1-xCo2O4 series,i.e. MgCo2O4,was also investigated. The sequence of the promotional effect was found to be: un-promoted < Li < Na < Cs < K-promoted catalyst. The reason for the increase in activity for the added alkali cations was electronic in nature. Additionally,the dependence of the activity on the K/Co ratio was also determined. The highest activity was obtained for the catalyst with a K/Co ratio of 0.05. A continuous decrease in activity was obtained for higher K/Co ratios. This decrease in activity was attributed to the elimination of mesoporosity in the catalysts with K/Co ratios > 0.05,based on N2 adsorption and scanning electron microscopy results.展开更多
Efficient and robust noble-metal-free bifunctional electrocatalysts for overall water splitting(OWS)is of great importance to realize the large-scale hydrogen production.Herein,we report the growth of undoped and Cr-d...Efficient and robust noble-metal-free bifunctional electrocatalysts for overall water splitting(OWS)is of great importance to realize the large-scale hydrogen production.Herein,we report the growth of undoped and Cr-doped NiCo2O4(Cr-NiCo2O4)nanoneedles(NNs)on nickel foam(NF)as bifunctional electrocatalysts for both hydrogen evolution reaction(HER)and oxygen evolution reaction(OER).We demonstrate that Cr-doping significantly improves activity for HER and OER by increasing the conductivity of NNs and allowing more active sites on NNs electrochemically accessible.When amorphous FeOOH is electrodeposited on the surface of Cr-NiCo2O4 NNs,the resulting FeOOH/Cr-NiCo2O4/NF exhibits itself as an excellent bifunctional catalyst for OWS.In the two-electrode cell where FeOOH/Cr-NiCo2O4/NF is used both as cathode and anode for OWS,a cell voltage of only 1.65 V is required to achieve an electrolysis current density of 100 mA·cm^−2.In addition,the catalyst shows a very high stability for OWS,the two-electrode cell can operate at a consist current density of 20 mA·cm^−2 for 10 h OWS with the cell voltage being stable at ca.1.60 V.These results demonstrate that FeOOH/Cr-NiCo2O4/NF possesses an OWS performance superior to most of transition-metal based bifunctional electrocatalysts working in alkaline medium.The excellent bifunctional activity and stability of FeOOH/Cr-NiCo2O4/NF are attributed to the following reasons:(i)The NN structure provides a large specific surface area;(ii)the high conductivity of Cr-NiCo2O4 enables more active centers on the far-end part of NNs to be electrochemically reached;(iii)the deposition of FeOOH supplies additional active sites for OWS.展开更多
The effect of the addition of small amounts of rare earths (Ln=La, Ce, Nd and Gd) to alumina supported copper-cobalt spinel oxide on the catalysts efficiency in CO and CH4 oxidation and in NO decomposition was inves...The effect of the addition of small amounts of rare earths (Ln=La, Ce, Nd and Gd) to alumina supported copper-cobalt spinel oxide on the catalysts efficiency in CO and CH4 oxidation and in NO decomposition was investigated. Samples of Ln/CuCo/AI catalyst were prepared and characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), atomic absorption spectroscopy (AAS), scanning electron mieroscopy-energy dispersive spectroscopy (SEM-EDS), H2-temperature-programmed reduc- tion (H2-TPR), electron paramagnetic resonanee (EPR) spectroscopy and low temperature nitrogen adsorption, The results showed that the addition of rare earths changed the surface state of the alumina supported copper-cobalt spinel catalyst. As a result, partial re- duction of copper species was observed as well as migration of these species between the surface and the bulk. The Ln/CuCo/A1 catalysts behaved differently in oxidation and reduction processes. In oxidation processes where oxide structure was important, Ce/CuCo/A1 and Nd/CuCo/A1 were the most active catalysts. The catalyst Ce/CuCo/AI was the most active in the oxidation reactions because of the availability and favorable surface distribution of the redox couples Cu+/Cu2+ and Ce3+/Ce4+. In NO decompostion, Ln-modified catalysts significantly improved the selectivity of the process to N2.展开更多
Regulating the selectivity of CO2 photoreduction is particularly challenging. Herein, we propose ideal models of atomic layers with/without element doping to investigate the effect of doping engineering to tune the se...Regulating the selectivity of CO2 photoreduction is particularly challenging. Herein, we propose ideal models of atomic layers with/without element doping to investigate the effect of doping engineering to tune the selectivity of CO2 photoreduction. Prototypical ZnCo2O4 atomic layers with/without Ni-doping were first synthesized. Density functional theory calculations reveal that introducing Ni atoms creates several new energy levels and increases the density-of-states at the conduction band minimum. Synchrotron radiation photoemission spectroscopy demonstrates that the band structures are suitable for CO2 photoreduction, while the surface photovoltage spectra demonstrate that Ni doping increases the carrier separation efficiency. In situ diffuse reflectance Fourier transform infrared spectra disclose that the CO2^- radical is the main intermediate, while temperature-programed desorption curves reveal that the ZnCo2O4 atomic layers with/without Ni doping favor the respective CO and CH4 desorption. The Ni-doped ZnCo2O4 atomic layers exhibit a 3.5-time higher CO selectivity than the ZnCo2O4 atomic layers. This work establishes a clear correlation between elemental doping and selectivity regulation for CO2 photoreduction, opening new possibilities for tailoring solar-driven photocatalytic behaviors.展开更多
Structural, magnetic and electrical properties of the La0.7Ca0.3Co1–xMnxO3(x=0, 0.7 and 1) samples prepared by a simple method were systematically studied and it was found that the crystal structure was transformed...Structural, magnetic and electrical properties of the La0.7Ca0.3Co1–xMnxO3(x=0, 0.7 and 1) samples prepared by a simple method were systematically studied and it was found that the crystal structure was transformed from rhombohedral for La0.7Ca0.3CoO3(LCCO) and La0.7Ca0.3Co0.3Mn0.7O3(LCCMO) samples to orthorhombic for La0.7Ca0.3MnO3(LCMO) sample. The AC magnetic susceptibility measurements showed that LCCO sample underwent a transition from paramagnetic(PM) to ferromagnetic(FM) phase at Curie temperature, TC^155 K and below Curie temperature, the glassy ferromagnetism nature was observed. In LCCMO sample,clear evidence of spin glass(SG) state was observed at low temperature. PM-FM phase transition at about TC^260 K and long range FM order at low temperatures were observed in LCMO sample. Both the LCCO and LCCMO samples exhibited insulating behavior in the whole range of measuring temperature whereas the LCMO sample underwent a clear metal-insulator(MI) transition at about TMI^263 K, corresponding to Curie temperature. Metallic region of ρ(T) curve of the LCMO sample was fitted to the model of electron-electron and electron-magnon scattering. The charge carrier transport behavior in all the samples was compared based on polaronic models.展开更多
Manganese cobaltite(MnCo_(2)_(4))is a promising electrode material because of its attractive redox chemistry and excellent charge storage capability.Our previous work demonstrated that the octahedrally-coordinated Mn ...Manganese cobaltite(MnCo_(2)_(4))is a promising electrode material because of its attractive redox chemistry and excellent charge storage capability.Our previous work demonstrated that the octahedrally-coordinated Mn are prone to react with the hydroxyl ions in alkaline electrolyte upon electrochemical cycling and separates on the surface of spinel to reconstruct into d-MnO_(2) nanosheets irreversibly,thus results in a change of the reaction mechanism with Kþion intercalation.However,the low capacity has greatly limited its practical application.Herein,we found that the tetrahedrally-coordinated Co_(2) þions were leached when MnCo_(2)_(4) was equilibrated in 1 mol L^(-1) HCl solution,leading to the formation of layered CoOOH on MnCo_(2)_(4) surface which is originated from the covalency competition induced selective breakage of the CoT–O bond in CoT–O–CoO and subsequent rearrangement of free Co_(6) octahedra.The as-formed CoOOH is stable upon cycling in alkaline electrolyte,exhibits conversion reaction mechanism with facile proton diffusion and is free of massive structural evolution,thus enables utilization of the bulk electrode material and realizes enhanced specific capacity as well as facilitated charge transfer and ion diffusion.In general,our work not only offers a feasible approach to deliberate modification of MnCo_(2)_(4)'s surface structure,but also provides an in-depth understanding of its charge storage mechanism,which enables rational design of the spinel oxides with promising charge storage properties.展开更多
The relation among electronic structure, chemical bond and thermoelectric property of Ca3 Co2 O6 and Ni-doped was studied by density function theory and discrete variation method(DFT-DVM). The results indicate that ...The relation among electronic structure, chemical bond and thermoelectric property of Ca3 Co2 O6 and Ni-doped was studied by density function theory and discrete variation method(DFT-DVM). The results indicate that the highest valence band( HVB )attd the lowest conduction band( LCB ) are mainly attribuled to Co3d, Ni3d and O2p atomic orbitals. The property of a semiconductor is shown from the gap between HVB and LCB. The gap of Ni-doped one is less than that of Ca3 Co2 O6. The non-metal bond or ceramic characteristic of Ni-doped one is weaker than that of Ca3 Co2 O6, but the metal characteristics of Ni-doped one are stronger than those of Ca3 Co2 O6. The thermoelectric property should be improved by adding Ni element into the system of Ca3 Co2 O6 .展开更多
The relation among electronic structure, chemical bond and thermoelectric property of Ca3 Co4 O9 was studied using density function and discrete variation method (DFT-DVM). The gap between the highest valence band ...The relation among electronic structure, chemical bond and thermoelectric property of Ca3 Co4 O9 was studied using density function and discrete variation method (DFT-DVM). The gap between the highest valence band (HVB) and the lowest conduction band (LCB) shows a semiconducting property. Ca3 Co4 O9 consists of CoO2 and Ca2 CoO3 two layers. The HVB and LCB near Fermi level are only mainly from O( 2 ) 2p and Co (2) 3d in Ca2 CoO3 layer. Therefore, the semiconducting or thermoelectric property of Ca3 Co4 O9 should be mainly from Ca2 CoO3 layer, but it seems to have no direct relation to the CoO2 layer, which is consistent with that binary oxides hardly have a thermoelectric property, but trinary oxide compounds have quite a good thermoelectric property. The covalent and ionic bonds of Ca2 CoO3 layer are both weaker than those of CoO2 layer. Ca plays the role of connections between CoO2 and Ca2 CoO3 layers in Ca3 Co4 O9, decrease the ionic and covalent bond strength, and improve the thermoelectric property.展开更多
The investigation of Sm-Ce doping on structure,conduction,and dielectric response of Bi_(2)Ca_(2-2x)Sm_(x)CexCoO_(6)(x=0.000,0.025,0.050,0.075)(BCSCCO)are presented.All the specimens were synthesized by a facile synth...The investigation of Sm-Ce doping on structure,conduction,and dielectric response of Bi_(2)Ca_(2-2x)Sm_(x)CexCoO_(6)(x=0.000,0.025,0.050,0.075)(BCSCCO)are presented.All the specimens were synthesized by a facile synthesis technique named the co-precipitation route.X-ray diffraction(XRD)reveals that BCSCCO crystallizes into one phase with space group P21/m.The crystallite size,dislocation density,lattice parameters,lattice strain,unit cell volume,and bulk density were determined using XRD data.The structural properties of Bi_(2)Ca_(2)CoO_(6)were examined using calculations based on the density functional theory.Theoretical and experimental values discrepancy is less than 1%.A scanning electron microscope was used for performing a microstructural analysis.The SEM images demonstrate the homogeneous distribution of grains with a range of sizes(0.054-0.090μm).The alternating current(ac)conductivity,dielectric permittivity,and tangent loss were also studied as a function of frequency(20 Hz-3 MHz)at different temperatures(100-500℃).All synthesized samples were examined using non-linear Debye's function to determine their spreading factor and relaxation time.The specimen with the lowest crystallite size(∼23 nm)exhibits a high dielectric permittivity(∼3.80×10^(6)).The conduction mechanism was examined in the studied samples with the use of Jonscher's power law.The power law indicates that the BCSCCO(x=0.000,0.025)follows correlated barrier hopping,whereas the x=0.050 and 0.075 compositions follow non-overlapping polaron tunneling.The studied specimen Bi_(2)Ca_(1.9)0Sm_(0.05)0Ce_(0.05)_(0)CoO_(6)with the highest density(∼5.65 g/cm^(3))displays a high electrical conductivity(∼46.1 S/cm).These findings correspond to those published for ceramics made from calcium cobaltite using solid-state reactions(5.0-26.0 S/cm).展开更多
Aqueous zinc-ion batteries(ZIBs) are attracting considerable attention because of their low cost,high safety and abundant anode material resources.However,the major challenge faced by aqueous ZIBs is the lack of stabl...Aqueous zinc-ion batteries(ZIBs) are attracting considerable attention because of their low cost,high safety and abundant anode material resources.However,the major challenge faced by aqueous ZIBs is the lack of stable and high capacity cathode materials due to their complicated reaction mechanism and slow Zn-ion transport kinetics.This study reports a unique 3 D ’flower-like’ zinc cobaltite(ZnCo_(2)O_(4-x)) with enriched oxygen vacancies as a new cathode material for aqueous ZIBs.Computational calculations reveal that the presence of oxygen vacancies significantly enhances the electronic conductivity and accelerates Zn^(2+) diffusion by providing enlarged channels.The as-fabricated batteries present an impressive specific capacity of 148.3 mAh g^(-1) at the current density of 0.05 A g^(-1),high energy(2.8 Wh kg^(-1)) and power densities(27.2 W kg^(-1)) based on the whole device,which outperform most of the reported aqueous ZIBs.Moreover,a flexible solid-state pouch cell was demonstrated,which delivers an extremely stable capacity under bending states.This work demonstrates that the performance of Zn-ion storage can be effectively enhanced by tailoring the atomic structure of cathode materials,guiding the development of low-cost and eco-friendly energy storage materials.展开更多
In this paper, a series of zinc cobaltite catalysts with the general formula Znx-Co1-xCo2O4 (x = 0.25, 0.50, 0.75 and 1.0) has been prepared using the co-precipitation method. Thermal analyzes (TGA and DTA) were used ...In this paper, a series of zinc cobaltite catalysts with the general formula Znx-Co1-xCo2O4 (x = 0.25, 0.50, 0.75 and 1.0) has been prepared using the co-precipitation method. Thermal analyzes (TGA and DTA) were used to follow up the thermal events accompanying the heat treatment of the parent mixture. Based on these results, the various parent mixtures were calcined at 500℃. The obtained solid catalysts were characterized by using XRD, FT-IR and N2-adsorption. The catalytic decomposition of N2O to N2 and O2 was carried out on the zinc-cobaltite catalysts. It was found that partial replacement of Co2+ by Zn2+ in Co3O4 spinel oxide led to a significant improvement in their N2O decomposition activity. Moreover, the catalytic activity was found to be depended on the calcination temperature utilized.展开更多
Hierarchical Ni CoO/PANI/CNTs hybrid composites were designed and fabricated having a layer of Ni CoOon the surface of PANI encapsulated CNTs with different morphologies. Physicochemical attributes of the synthesized ...Hierarchical Ni CoO/PANI/CNTs hybrid composites were designed and fabricated having a layer of Ni CoOon the surface of PANI encapsulated CNTs with different morphologies. Physicochemical attributes of the synthesized composites were examined by FTIR, UV–visible and X-ray diffraction(XRD)techniques. Morphological aspects were evaluated by field-emission scanning microscopy(FESEM),electron diffraction spectroscopy(EDS), high resolution transmission electron microscopy(HRTEM) and selected area electron diffraction(SAED) studies. Electrochemical measurements revealed an improved specific capacitance of 2250 F/g at a scan rate of 5 m V/s and 2000 F/g at a current density of 1 A/g with good rate capability using a three-electrode system. These enhanced features are achieved from the well designed nanostructure and the synergistic contributions of individual components in the electrode material.展开更多
The electric measurements were carried out for La0.8Sr0.2CoO3 nanoceramics by using impedance spectroscopy methods. The resistance of sample was practically independent of frequency in measurement range. Its dependenc...The electric measurements were carried out for La0.8Sr0.2CoO3 nanoceramics by using impedance spectroscopy methods. The resistance of sample was practically independent of frequency in measurement range. Its dependence on reciprocal temperature showed quite complicated mechanism of conduction. The most striking property of investigated sample was its resistance decreasing with increasing applied polarization.展开更多
The layered cobaltite Ca 2.6Nd 0.4Co 4O 9 was synthesized by the solid-state reaction. Their crystal structure was determined by the X-ray powder diffraction and CELL program. The prepared Ca 2.6Nd 0.4Co...The layered cobaltite Ca 2.6Nd 0.4Co 4O 9 was synthesized by the solid-state reaction. Their crystal structure was determined by the X-ray powder diffraction and CELL program. The prepared Ca 2.6Nd 0.4Co 4O 9 compound has the monoclinic symmetry. The electrical conductivity and Seebeck coefficient were measured from room temperature to 700 ℃ in air. Both the properties increase while rising temperature. The thermoelectric power of Ca 2.6Nd 0.4Co 4O 9 is about 242 4 μV·K -1. The results imply a promising way to enhance the thermoelectric properties of the layered cobaltite oxides by optimizing their composition and microstructure.展开更多
文摘The direct decomposition of N2O was investigated over a series of magnesium cobaltite catalysts,MgxCo1-xCo2O4(0.0 ≤ x ≤ 1.0) ,which were prepared by the thermal decomposition of stoichiometric amounts of magnesium hydroxide and cobalt acetate. The thermal genesis of the different catalysts from their precursors was explored using thermogravimetric analysis,differential thermal analysis,and X-ray diffraction. Texture analysis was carried out using N2 adsorption at -196 °C. We found that all the catalysts that were calcined at 500 °C have a spinel structure. N2O decomposition activity was found to increase with an increase in the spinel structure's magnesium content. The influence of alkali cation promoters(Li,Na,K,and Cs) on the activity of the most active catalyst in the MgxCo1-xCo2O4 series,i.e. MgCo2O4,was also investigated. The sequence of the promotional effect was found to be: un-promoted < Li < Na < Cs < K-promoted catalyst. The reason for the increase in activity for the added alkali cations was electronic in nature. Additionally,the dependence of the activity on the K/Co ratio was also determined. The highest activity was obtained for the catalyst with a K/Co ratio of 0.05. A continuous decrease in activity was obtained for higher K/Co ratios. This decrease in activity was attributed to the elimination of mesoporosity in the catalysts with K/Co ratios > 0.05,based on N2 adsorption and scanning electron microscopy results.
基金We gratefully acknowledge the financial support of this work by the National Natural Science Foundation of China(Nos.51872015 and 51672017).
文摘Efficient and robust noble-metal-free bifunctional electrocatalysts for overall water splitting(OWS)is of great importance to realize the large-scale hydrogen production.Herein,we report the growth of undoped and Cr-doped NiCo2O4(Cr-NiCo2O4)nanoneedles(NNs)on nickel foam(NF)as bifunctional electrocatalysts for both hydrogen evolution reaction(HER)and oxygen evolution reaction(OER).We demonstrate that Cr-doping significantly improves activity for HER and OER by increasing the conductivity of NNs and allowing more active sites on NNs electrochemically accessible.When amorphous FeOOH is electrodeposited on the surface of Cr-NiCo2O4 NNs,the resulting FeOOH/Cr-NiCo2O4/NF exhibits itself as an excellent bifunctional catalyst for OWS.In the two-electrode cell where FeOOH/Cr-NiCo2O4/NF is used both as cathode and anode for OWS,a cell voltage of only 1.65 V is required to achieve an electrolysis current density of 100 mA·cm^−2.In addition,the catalyst shows a very high stability for OWS,the two-electrode cell can operate at a consist current density of 20 mA·cm^−2 for 10 h OWS with the cell voltage being stable at ca.1.60 V.These results demonstrate that FeOOH/Cr-NiCo2O4/NF possesses an OWS performance superior to most of transition-metal based bifunctional electrocatalysts working in alkaline medium.The excellent bifunctional activity and stability of FeOOH/Cr-NiCo2O4/NF are attributed to the following reasons:(i)The NN structure provides a large specific surface area;(ii)the high conductivity of Cr-NiCo2O4 enables more active centers on the far-end part of NNs to be electrochemically reached;(iii)the deposition of FeOOH supplies additional active sites for OWS.
基金Project supported by the European Social Fund(ESF)(BG051PO001-3.3.06-0050)
文摘The effect of the addition of small amounts of rare earths (Ln=La, Ce, Nd and Gd) to alumina supported copper-cobalt spinel oxide on the catalysts efficiency in CO and CH4 oxidation and in NO decomposition was investigated. Samples of Ln/CuCo/AI catalyst were prepared and characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), atomic absorption spectroscopy (AAS), scanning electron mieroscopy-energy dispersive spectroscopy (SEM-EDS), H2-temperature-programmed reduc- tion (H2-TPR), electron paramagnetic resonanee (EPR) spectroscopy and low temperature nitrogen adsorption, The results showed that the addition of rare earths changed the surface state of the alumina supported copper-cobalt spinel catalyst. As a result, partial re- duction of copper species was observed as well as migration of these species between the surface and the bulk. The Ln/CuCo/A1 catalysts behaved differently in oxidation and reduction processes. In oxidation processes where oxide structure was important, Ce/CuCo/A1 and Nd/CuCo/A1 were the most active catalysts. The catalyst Ce/CuCo/AI was the most active in the oxidation reactions because of the availability and favorable surface distribution of the redox couples Cu+/Cu2+ and Ce3+/Ce4+. In NO decompostion, Ln-modified catalysts significantly improved the selectivity of the process to N2.
文摘Regulating the selectivity of CO2 photoreduction is particularly challenging. Herein, we propose ideal models of atomic layers with/without element doping to investigate the effect of doping engineering to tune the selectivity of CO2 photoreduction. Prototypical ZnCo2O4 atomic layers with/without Ni-doping were first synthesized. Density functional theory calculations reveal that introducing Ni atoms creates several new energy levels and increases the density-of-states at the conduction band minimum. Synchrotron radiation photoemission spectroscopy demonstrates that the band structures are suitable for CO2 photoreduction, while the surface photovoltage spectra demonstrate that Ni doping increases the carrier separation efficiency. In situ diffuse reflectance Fourier transform infrared spectra disclose that the CO2^- radical is the main intermediate, while temperature-programed desorption curves reveal that the ZnCo2O4 atomic layers with/without Ni doping favor the respective CO and CH4 desorption. The Ni-doped ZnCo2O4 atomic layers exhibit a 3.5-time higher CO selectivity than the ZnCo2O4 atomic layers. This work establishes a clear correlation between elemental doping and selectivity regulation for CO2 photoreduction, opening new possibilities for tailoring solar-driven photocatalytic behaviors.
基金the Payame Noor University for supporting this work
文摘Structural, magnetic and electrical properties of the La0.7Ca0.3Co1–xMnxO3(x=0, 0.7 and 1) samples prepared by a simple method were systematically studied and it was found that the crystal structure was transformed from rhombohedral for La0.7Ca0.3CoO3(LCCO) and La0.7Ca0.3Co0.3Mn0.7O3(LCCMO) samples to orthorhombic for La0.7Ca0.3MnO3(LCMO) sample. The AC magnetic susceptibility measurements showed that LCCO sample underwent a transition from paramagnetic(PM) to ferromagnetic(FM) phase at Curie temperature, TC^155 K and below Curie temperature, the glassy ferromagnetism nature was observed. In LCCMO sample,clear evidence of spin glass(SG) state was observed at low temperature. PM-FM phase transition at about TC^260 K and long range FM order at low temperatures were observed in LCMO sample. Both the LCCO and LCCMO samples exhibited insulating behavior in the whole range of measuring temperature whereas the LCMO sample underwent a clear metal-insulator(MI) transition at about TMI^263 K, corresponding to Curie temperature. Metallic region of ρ(T) curve of the LCMO sample was fitted to the model of electron-electron and electron-magnon scattering. The charge carrier transport behavior in all the samples was compared based on polaronic models.
基金supported by the National Key Research and Development Program of China(2022YFE0206300)the National Natural Science Foundation of China(22209047,U21A2081,22075074)+2 种基金Natural Science Foundation of Hunan Province(2020JJ5035)Hunan Provincial Department of Education Outstanding Youth Project(23B0037)Macao Science and Technology Development Fund(Macao SAR,FDCT-0096/2020/A2).
文摘Manganese cobaltite(MnCo_(2)_(4))is a promising electrode material because of its attractive redox chemistry and excellent charge storage capability.Our previous work demonstrated that the octahedrally-coordinated Mn are prone to react with the hydroxyl ions in alkaline electrolyte upon electrochemical cycling and separates on the surface of spinel to reconstruct into d-MnO_(2) nanosheets irreversibly,thus results in a change of the reaction mechanism with Kþion intercalation.However,the low capacity has greatly limited its practical application.Herein,we found that the tetrahedrally-coordinated Co_(2) þions were leached when MnCo_(2)_(4) was equilibrated in 1 mol L^(-1) HCl solution,leading to the formation of layered CoOOH on MnCo_(2)_(4) surface which is originated from the covalency competition induced selective breakage of the CoT–O bond in CoT–O–CoO and subsequent rearrangement of free Co_(6) octahedra.The as-formed CoOOH is stable upon cycling in alkaline electrolyte,exhibits conversion reaction mechanism with facile proton diffusion and is free of massive structural evolution,thus enables utilization of the bulk electrode material and realizes enhanced specific capacity as well as facilitated charge transfer and ion diffusion.In general,our work not only offers a feasible approach to deliberate modification of MnCo_(2)_(4)'s surface structure,but also provides an in-depth understanding of its charge storage mechanism,which enables rational design of the spinel oxides with promising charge storage properties.
文摘The relation among electronic structure, chemical bond and thermoelectric property of Ca3 Co2 O6 and Ni-doped was studied by density function theory and discrete variation method(DFT-DVM). The results indicate that the highest valence band( HVB )attd the lowest conduction band( LCB ) are mainly attribuled to Co3d, Ni3d and O2p atomic orbitals. The property of a semiconductor is shown from the gap between HVB and LCB. The gap of Ni-doped one is less than that of Ca3 Co2 O6. The non-metal bond or ceramic characteristic of Ni-doped one is weaker than that of Ca3 Co2 O6, but the metal characteristics of Ni-doped one are stronger than those of Ca3 Co2 O6. The thermoelectric property should be improved by adding Ni element into the system of Ca3 Co2 O6 .
基金Funded by the National Natural Science Foundation of China(No.20271040)
文摘The relation among electronic structure, chemical bond and thermoelectric property of Ca3 Co4 O9 was studied using density function and discrete variation method (DFT-DVM). The gap between the highest valence band (HVB) and the lowest conduction band (LCB) shows a semiconducting property. Ca3 Co4 O9 consists of CoO2 and Ca2 CoO3 two layers. The HVB and LCB near Fermi level are only mainly from O( 2 ) 2p and Co (2) 3d in Ca2 CoO3 layer. Therefore, the semiconducting or thermoelectric property of Ca3 Co4 O9 should be mainly from Ca2 CoO3 layer, but it seems to have no direct relation to the CoO2 layer, which is consistent with that binary oxides hardly have a thermoelectric property, but trinary oxide compounds have quite a good thermoelectric property. The covalent and ionic bonds of Ca2 CoO3 layer are both weaker than those of CoO2 layer. Ca plays the role of connections between CoO2 and Ca2 CoO3 layers in Ca3 Co4 O9, decrease the ionic and covalent bond strength, and improve the thermoelectric property.
基金Project supported by the NRPU-Higher Education Commission,Pakistan。
文摘The investigation of Sm-Ce doping on structure,conduction,and dielectric response of Bi_(2)Ca_(2-2x)Sm_(x)CexCoO_(6)(x=0.000,0.025,0.050,0.075)(BCSCCO)are presented.All the specimens were synthesized by a facile synthesis technique named the co-precipitation route.X-ray diffraction(XRD)reveals that BCSCCO crystallizes into one phase with space group P21/m.The crystallite size,dislocation density,lattice parameters,lattice strain,unit cell volume,and bulk density were determined using XRD data.The structural properties of Bi_(2)Ca_(2)CoO_(6)were examined using calculations based on the density functional theory.Theoretical and experimental values discrepancy is less than 1%.A scanning electron microscope was used for performing a microstructural analysis.The SEM images demonstrate the homogeneous distribution of grains with a range of sizes(0.054-0.090μm).The alternating current(ac)conductivity,dielectric permittivity,and tangent loss were also studied as a function of frequency(20 Hz-3 MHz)at different temperatures(100-500℃).All synthesized samples were examined using non-linear Debye's function to determine their spreading factor and relaxation time.The specimen with the lowest crystallite size(∼23 nm)exhibits a high dielectric permittivity(∼3.80×10^(6)).The conduction mechanism was examined in the studied samples with the use of Jonscher's power law.The power law indicates that the BCSCCO(x=0.000,0.025)follows correlated barrier hopping,whereas the x=0.050 and 0.075 compositions follow non-overlapping polaron tunneling.The studied specimen Bi_(2)Ca_(1.9)0Sm_(0.05)0Ce_(0.05)_(0)CoO_(6)with the highest density(∼5.65 g/cm^(3))displays a high electrical conductivity(∼46.1 S/cm).These findings correspond to those published for ceramics made from calcium cobaltite using solid-state reactions(5.0-26.0 S/cm).
基金supported by the National Natural Science Foundation of China(Nos.51873198,51503184 and 21703248)the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDB20000000)+1 种基金the Engineering and Physical Sciences Research Council(EPSRC,EP/R023581/1)the RSC Mobility Grant(M19-7656)and the STFC Batteries Network(ST/R006873/1)。
文摘Aqueous zinc-ion batteries(ZIBs) are attracting considerable attention because of their low cost,high safety and abundant anode material resources.However,the major challenge faced by aqueous ZIBs is the lack of stable and high capacity cathode materials due to their complicated reaction mechanism and slow Zn-ion transport kinetics.This study reports a unique 3 D ’flower-like’ zinc cobaltite(ZnCo_(2)O_(4-x)) with enriched oxygen vacancies as a new cathode material for aqueous ZIBs.Computational calculations reveal that the presence of oxygen vacancies significantly enhances the electronic conductivity and accelerates Zn^(2+) diffusion by providing enlarged channels.The as-fabricated batteries present an impressive specific capacity of 148.3 mAh g^(-1) at the current density of 0.05 A g^(-1),high energy(2.8 Wh kg^(-1)) and power densities(27.2 W kg^(-1)) based on the whole device,which outperform most of the reported aqueous ZIBs.Moreover,a flexible solid-state pouch cell was demonstrated,which delivers an extremely stable capacity under bending states.This work demonstrates that the performance of Zn-ion storage can be effectively enhanced by tailoring the atomic structure of cathode materials,guiding the development of low-cost and eco-friendly energy storage materials.
文摘In this paper, a series of zinc cobaltite catalysts with the general formula Znx-Co1-xCo2O4 (x = 0.25, 0.50, 0.75 and 1.0) has been prepared using the co-precipitation method. Thermal analyzes (TGA and DTA) were used to follow up the thermal events accompanying the heat treatment of the parent mixture. Based on these results, the various parent mixtures were calcined at 500℃. The obtained solid catalysts were characterized by using XRD, FT-IR and N2-adsorption. The catalytic decomposition of N2O to N2 and O2 was carried out on the zinc-cobaltite catalysts. It was found that partial replacement of Co2+ by Zn2+ in Co3O4 spinel oxide led to a significant improvement in their N2O decomposition activity. Moreover, the catalytic activity was found to be depended on the calcination temperature utilized.
基金the financial assistance in the form of major research project from TDT Division of Department of Science and Technology,Government of India(DST reference no:DST/TSG/PT/2009/116-G)
文摘Hierarchical Ni CoO/PANI/CNTs hybrid composites were designed and fabricated having a layer of Ni CoOon the surface of PANI encapsulated CNTs with different morphologies. Physicochemical attributes of the synthesized composites were examined by FTIR, UV–visible and X-ray diffraction(XRD)techniques. Morphological aspects were evaluated by field-emission scanning microscopy(FESEM),electron diffraction spectroscopy(EDS), high resolution transmission electron microscopy(HRTEM) and selected area electron diffraction(SAED) studies. Electrochemical measurements revealed an improved specific capacitance of 2250 F/g at a scan rate of 5 m V/s and 2000 F/g at a current density of 1 A/g with good rate capability using a three-electrode system. These enhanced features are achieved from the well designed nanostructure and the synergistic contributions of individual components in the electrode material.
文摘The electric measurements were carried out for La0.8Sr0.2CoO3 nanoceramics by using impedance spectroscopy methods. The resistance of sample was practically independent of frequency in measurement range. Its dependence on reciprocal temperature showed quite complicated mechanism of conduction. The most striking property of investigated sample was its resistance decreasing with increasing applied polarization.
文摘The layered cobaltite Ca 2.6Nd 0.4Co 4O 9 was synthesized by the solid-state reaction. Their crystal structure was determined by the X-ray powder diffraction and CELL program. The prepared Ca 2.6Nd 0.4Co 4O 9 compound has the monoclinic symmetry. The electrical conductivity and Seebeck coefficient were measured from room temperature to 700 ℃ in air. Both the properties increase while rising temperature. The thermoelectric power of Ca 2.6Nd 0.4Co 4O 9 is about 242 4 μV·K -1. The results imply a promising way to enhance the thermoelectric properties of the layered cobaltite oxides by optimizing their composition and microstructure.