The study aims to investigate the carbonated water erosion mechanism of lining concrete in tunnels traversing karst environment and enhance its resistance.In this study,dynamic carbonated water erosion was simulated t...The study aims to investigate the carbonated water erosion mechanism of lining concrete in tunnels traversing karst environment and enhance its resistance.In this study,dynamic carbonated water erosion was simulated to assess erosion depth,microstructure,phase migrations,and pore structure in various tunnel lining cement-based materials.Additionally,Ca^(2+)leaching was analyzed,and impact of Ca/Si molar ratio in hydration products on erosion resistance was discussed by thermodynamic calculations.The results indicate that carbonated water erosion caused rough and porous surface on specimens,with reduced portlandite and CaCO_(3) content,increased porosity,and an enlargement of pore size.The thermodynamic calculations indicate that the erosion is spontaneous,driven by physical dissolution and chemical reactions dominated by Gibbs free energy.And the erosion reactions proceed more spontaneously and extensively when Ca/Si molar ratio in hydration products was higher.Therefore,cement-based materials with higher portlandite content exhibit weaker erosion resistance.Model-building concrete,with C-S-H gel and portlandite as primary hydration products,has greater erosion susceptibility than shotcrete with ettringite as main hydration product.Moreover,adding silicon-rich mineral admixtures can enhance the erosion resistance.This research offers theory and tech insights to boost cement-based material resistance against carbonated water erosion in karst tunnel engineering.展开更多
The design and synthesis of a novel π-conjugated fiuorescent framework by external ligand-assisted C-H olefination of heterocycles with excellent regioselectivity and broad substrate scope are reported herein.These n...The design and synthesis of a novel π-conjugated fiuorescent framework by external ligand-assisted C-H olefination of heterocycles with excellent regioselectivity and broad substrate scope are reported herein.These novel fiuorescent materials could present full-color-tunable emissions with large Stokes shifts. Furthermore, the protocol provides an opportunity to rapidly screen novel organic single-molecule whitelight materials with high fiuorescence quantum yields. The robust organic and low-cost white lightemitting diodes could rapidly be fabricated using the white-light-emitting material. Experimental data and theoretical calculations indicate that in the white-light dual emission the relatively short wavelength from high-lying singlet state emission and the relatively long wavelength from low-lying singlet state emission. The anti-Kasha dual-emission systems will provide a foundation for the development and application of organic single-molecule white light materials, effectively promoting the development and innovation of luminescent materials. In addition, this method demonstrated its potential application in the synthesis of new near-infrared(NIR) fiuorescence materials with large Stokes shifts based on the olefination of heterocycles.展开更多
While silicon/carbon(Si/C)is considered one of the most promising anode materials for the next generation of high-energy lithium-ion batteries(LIBs),the industrialization of Si/C anodes is hampered by high-cost and lo...While silicon/carbon(Si/C)is considered one of the most promising anode materials for the next generation of high-energy lithium-ion batteries(LIBs),the industrialization of Si/C anodes is hampered by high-cost and low product yield.Herein,a high-yield strategy is developed in which photovoltaic waste silicon is converted to cost-effective graphitic Si/C composites(G-Si@C)for LIBs.The introduction of a binder improves the dispersion and compatibility of silicon and graphite,enhances particle sphericity,and significantly reduces the loss rate of the spray prilling process(from about 25%to 5%).As an LIB anode,the fabricated G-Si@C composites exhibit a capacity of 605 mAh g^(-1) after 1200 cycles.The cost of manufacturing Si/C anode materials has been reduced to approximately$7.47 kg^(-1),which is close to that of commercial graphite anode materials($5.0 kg^(-1)),and significantly lower than commercial Si/C materials(ca.$20.74 kg^(-1)).Moreover,the G-Si@C material provides approximately 81.0 Ah/$of capacity,which exceeds the current best commercial graphite anodes(70.0 Ah/$)and Si/C anodes(48.2 Ah/$).The successful implementation of this pathway will significantly promote the industrialization of high-energydensity Si/C anode materials.展开更多
Tin dioxide(SnO_(2))with a high theoretical specific capacity of 1494 mAh g^(-1)is a promising candidate anode material for lithium storage.However,the shortcomings of serious volume expansion and low conductivity lim...Tin dioxide(SnO_(2))with a high theoretical specific capacity of 1494 mAh g^(-1)is a promising candidate anode material for lithium storage.However,the shortcomings of serious volume expansion and low conductivity limit its wide application.Herein,coaxial nano-multilayered C/SnO_(2)/TiO_(2)composites were fabricated via layerby-layer self-assembly of TiO_(2)and SnO_(2)-gel layers on the natural cellulose filter paper,followed by thermal treatment under a nitrogen atmosphere.Through engineering design of the assembly process,the optimal C/SinO_(2)/TiO_(2)composite features five alternating SnO_(2)and TiO_(2)nanolayers,with TiO_(2)as the outside shell(denoted as C/TSTST).This unique structure endows the C/TSTST with excellent structural stability and electrochemical kinetics,making it a high-performance anode for lithium-ion batteries(LIBs).The C/TSTST composite delivers a high reversible capacity of 676 mAh g^(-1)at 0.1 A g^(-1)after 200 cycles and retains a capacity of 504 mAh g^(-1)at 1.0 A g^(-1),which can be recovered to 781 mAh g^(-1)at 0.1 A g^(-1)The significantly enhanced electrochemical performance is attributed to the hierarchical hybrid structure,where the carbon core combined with coaxial TiO_(2)nanolayers serves as a structural scaffold,ameliorating volume change of SnO_(2)while creating abundant interfacial defects for enhanced lithium storage and rapid charge transport.These findings are further demonstrated by the density functional theory(DFT)calculations.This work provides an efficient strategy for designing coaxial nano-multilayered transition metal oxide-related electrode materials,offering new insights into high-performance LIBs anodes.展开更多
The oilseed cake, vetch, rapeseed straw, wheat straw and corn straw were buried in tobacco-planted soil. The decomposition rates, the variation of active organic C and N contents in the residues and the relationship b...The oilseed cake, vetch, rapeseed straw, wheat straw and corn straw were buried in tobacco-planted soil. The decomposition rates, the variation of active organic C and N contents in the residues and the relationship between active organic C and N contents and decomposition rate were investigated. The results showed the decomposition rates of different organic materials were all high in the early period and then low in the late period. Among the organic materials, the decomposition rates ranked as oilseed cake 〉 vetch 〉 wheat straw and rapeseed straw 〉 corn straw. The decomposition rate was positively related to total N content （P〈0.01）, but was negatively related to the active organic C/N ratio （P〈0.01）. However, there was no significant relationship between decomposition ratio and active organic C content. With the proceeding of decomposition, the active organic C content and the total N content in rapeseed straw, vetch, wheat straw and corn straw all trended to increase, but the active organic C/N ratio trended to decrease. However, the variation of active organic C content, total N content and active organic C/N ratio in oilseed cake was on the contrary.展开更多
The LiMnPO4/C composite material was synthesized via a sol-gel method based on the citric acid. The X-ray diffraction （XRD）, scanning electron microscopy （SEM） and electrochemical performance tests were adopted to...The LiMnPO4/C composite material was synthesized via a sol-gel method based on the citric acid. The X-ray diffraction （XRD）, scanning electron microscopy （SEM） and electrochemical performance tests were adopted to characterize the properties of LiMnPO4/C. The XRD studies show that the pure olivine phase LiMnPO4 can be obtained at a low temperature of 500 °C. The SEM analyses illustrate that the citric acid used as the chelating reagent and carbon source can restrain the particle size of LiMnPO4/C well. The LiMnPO4/C sample synthesized at 500 °C for 10 h performs the highest initial discharge capacity of 122.6 mA-h/g, retaining 112.4 mA-h/g over 30 cycles at 0.05C rate. The citric acid based sol-gel method is favor to obtain the high electrochemical performance of LiMnPO4/C.展开更多
Silicon/flake graphite/carbon （Si/FG/C） composites were synthesized with different dispersants via spray drying and subsequent pyrolysis, and effects of dispersants on the characteristics of the composites were inve...Silicon/flake graphite/carbon （Si/FG/C） composites were synthesized with different dispersants via spray drying and subsequent pyrolysis, and effects of dispersants on the characteristics of the composites were investigated. The structure and properties of the composites were determined by X-ray diffractometry （XRD）, scanning electron microscopy （SEM） and electrochemical measurements. The results show that samples have silicon/flake graphite/amorphous carbon composite structure, good spherical appearances, and better electrochemical performance than pure nano-Si and FG/C composites. Compared with the Si/FG/C composite using washing powder as dispersant, the Si/FG/C composite using sodium dodecyl benzene sulfonate （SDBS） as dispersant has better electrochemical performance with a reversible capacity of 602.68 mA·h/g, and a capacity retention ratio of 91.58 % after 20 cycles.展开更多
Inorganic materials can solve transportable and on-site hydrolytic hydrogen generation issues.CaH_(2)/(Al/Si)composites are preferable due to their notable chemical properties.However,these composites require pretreat...Inorganic materials can solve transportable and on-site hydrolytic hydrogen generation issues.CaH_(2)/(Al/Si)composites are preferable due to their notable chemical properties.However,these composites require pretreatments,an inert environment,and long hours of physical ball milling for high homogeneity and synergistic effects.CaH_(2)also inhibits the hydrolysis reaction by forming its products on the Al/Si surface,which hinders the direct utilization of composites.This work represents the first investigation of NaH-CaH_(2)(Al/Si)fuel composites,which greatly overcome these limitations and can be directly used for on-site hydrogen generation and proton exchange membrane(PEM)fuel cells.The NaH-CaH_(2)(Al/Si)fuel composites were prepared by using a straightforward mixing method with variable composition ratios,showing high H_(2)yield and fuel cell(FC)performance.NaH addition provides the bridge effect,which opens up a new way to enable efficient hydrolysis and greatly enhances the hydrolysis activity of CaH_(2)/(Al/Si)composites.The novel fuel composites(NaH-CaH_(2)/Al)have extraordinary FC performance and a 0.42 W/cm2 peak power density greater than commercial hydrogen generators.It provides high H_(2)yield 84.4%for NaH-CaH_(2)/Al and 82%for NaH-CaH_(2)/Si compared to NaOH-CaH_(2)(Al/Si),NaCl-CaH_(2)(Al/Si),and KCl-CaH_(2)(Al/Si)composites.The NaH bridge effect hinders the direct water contact and stops the formation of Ca(OH)2 around Al/Si,which provides adequate pathways for the CaH_(2)(Al/Si)hydrolysis.The impressive capabilities of novel fuel composites are anticipated to offer practical uses in fuel cells,automobile applications,and portable/on-board H_(2)generation.展开更多
In order to enhance electrochemical properties of LiFePO4 （LFP） cathode materials, spherical porous nano/micro structured LFP/C cathode materials were synthesized by spray drying, followed by calcination. The result...In order to enhance electrochemical properties of LiFePO4 （LFP） cathode materials, spherical porous nano/micro structured LFP/C cathode materials were synthesized by spray drying, followed by calcination. The results show that the spherical precursors with the sizes of 0.5-5 μm can be completely converted to LFP/C when the calcination temperature is higher than 500 ℃. The LFP/C microspheres obtained at calcination temperature of 700 ℃ are composed of numerous particles with sizes of -20 nm, and have well-developed interconnected pore structure and large specific surface area of 28.77 mE/g. The specific discharge capacities of the LFP/C obtained at 700 ℃ are 162.43, 154.35 and 144.03 mA.h/g at 0.5C, 1C and 2C, respectively. Meanwhile, the capacity retentions can reach up to 100% after 50 cycles. The improved electrochemical properties of the materials are ascribed to a small Li＋ diffusion resistance and special structure of LFP/C microspheres.展开更多
Researching for interphase materials that can protect SiC fibers from oxygen and water vapor attacks has become one of the most important issues for the applications of SiC_f/SiC composites in high-temperature combust...Researching for interphase materials that can protect SiC fibers from oxygen and water vapor attacks has become one of the most important issues for the applications of SiC_f/SiC composites in high-temperature combustion environment. However, such kinds of interphase materials are not available yet. Herein,we report theoretically predicted properties of two promising interphase materials Y_5Si_3 C and Y_3Si_2C_2.Although crystallizing in different structures, they share the common features of layered structure,anisotropic chemical bonding, anisotropic electrical and mechanical properties, and low shear deformation resistance. The bulk moduli for Y_5Si_3C and Y_3Si_2C_2 are 78 and 93 GPa, respectively; while their shear moduli are 52 and 50GPa, respectively. The maximum to minimum Young's modulus ratios are1.44 for Y_5Si_3C and 3.27 for Y_3Si_2C_2. Based on the low shear deformation resistance and low Pugh's ratios(G/B = 0.666 forY_5Si_3C and 0.537 for Y_3Si_2C_2; G: shear modulus; B: bulk modulus), they are predicted as damage tolerant and soft ceramics with predicted Vickers hardness of 9.6 and 6.9 GPa, respectively.The cleavage plane and possible slip systems are(000 l) and(0001)[1120] and(1010)[0001] forY_5Si_3C,and those for Y_3Si_2C_2 are {h00} and(010)[101]. Since the oxidation products are water-vapor resistant Y2 Si2 O7, Y2 SiO5 and/or Y_2 O_3 upon oxidation, and the volume expansions are ca 140% and ca 26% for Y_5Si_3C and Y_3Si_2C_2, they are expected to seal the interfacial cracks in SiC_f/SiC composites. The unique combination of easy cleavage, low shear deformation resistance, volume expansions upon oxidation, and the resistance of the oxidation products to water vapor attack warrant them promising as interphase materials of SiC_f/SiC composites for water-vapor laden environment applications.展开更多
Spherical LiFePO4 and LiFePO4/C composite powders for lithium ion batteries were synthesized by a novel processing route of co-precipitation and subsequent calcinations in a nitrogen and hydrogen atmosphere. The precu...Spherical LiFePO4 and LiFePO4/C composite powders for lithium ion batteries were synthesized by a novel processing route of co-precipitation and subsequent calcinations in a nitrogen and hydrogen atmosphere. The precursors of LiFePO4, LiFePO4/C composite and the resultant products were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), and the electrochemical performances were investigated by galvanostatic charge and discharge tests. The precursors composed of amorphous Fe3(PO4)2·xH2O and crystalline Li3PO4 obtained in the co-precipitation processing have a sphere-like morphology. The spherical LiFePO4 derived from the calcinations of the precursor at 700 ℃ for 10 h in a reduction atmosphere shows a discharge capacity of 119 mAh·g-1 at the C/10 rate, while the LiFePO4/C composite with 10wt.% carbon addition exhibits a discharge capacity of 140 mAh·g-1. The electrochemical performances indicate that the LiFePO4/C composite has a higher specific capacity and a more stable cycling performance than the bare olivine LiFePO4 due to the carbon addition enhancing the electronic conductivity.展开更多
Data-mining techniques using machine learning are powerful and efficient for materials design, possessing great potential for discovering new materials with good characteristics. Here, this technique has been used on ...Data-mining techniques using machine learning are powerful and efficient for materials design, possessing great potential for discovering new materials with good characteristics. Here, this technique has been used on composition design for La（Fe,Si/Al）（13）-based materials, which are regarded as one of the most promising magnetic refrigerants in practice. Three prediction models are built by using a machine learning algorithm called gradient boosting regression tree（GBRT） to essentially find the correlation between the Curie temperature（TC）, maximum value of magnetic entropy change（（？SM）（max））,and chemical composition, all of which yield high accuracy in the prediction of TC and（？SM）（max）. The performance metric coefficient scores of determination（R^2） for the three models are 0.96, 0.87, and 0.91. These results suggest that all of the models are well-developed predictive models on the challenging issue of generalization ability for untrained data, which can not only provide us with suggestions for real experiments but also help us gain physical insights to find proper composition for further magnetic refrigeration applications.展开更多
Ti3C2Tx,a novel two-dimensional layer material,is widely used as electrode materials of supercapacitor due to its good metal conductivity,redox reaction active surface,and so on.However,there are many challenges to be...Ti3C2Tx,a novel two-dimensional layer material,is widely used as electrode materials of supercapacitor due to its good metal conductivity,redox reaction active surface,and so on.However,there are many challenges to be addressed which impede Ti3C2Tx obtaining the ideal specific capacitance,such as restacking,re-crushing,and oxidation of titanium.Recently,many advances have been proposed to enhance capacitance performance of Ti3C2Tx.In this review,recent strategies for improving specific capacitance are summarized and compared,for example,film formation,surface modification,and composite method.Furthermore,in order to comprehend the mechanism of those efforts,this review analyzes the energy storage performance in different electrolytes and influencing factors.This review is expected to predict redouble research direction of Ti3C2Tx materials in supercapacitors.展开更多
基金Project(2021YJ059)supported by the Research Project of China Academy of Railway Sciences。
文摘The study aims to investigate the carbonated water erosion mechanism of lining concrete in tunnels traversing karst environment and enhance its resistance.In this study,dynamic carbonated water erosion was simulated to assess erosion depth,microstructure,phase migrations,and pore structure in various tunnel lining cement-based materials.Additionally,Ca^(2+)leaching was analyzed,and impact of Ca/Si molar ratio in hydration products on erosion resistance was discussed by thermodynamic calculations.The results indicate that carbonated water erosion caused rough and porous surface on specimens,with reduced portlandite and CaCO_(3) content,increased porosity,and an enlargement of pore size.The thermodynamic calculations indicate that the erosion is spontaneous,driven by physical dissolution and chemical reactions dominated by Gibbs free energy.And the erosion reactions proceed more spontaneously and extensively when Ca/Si molar ratio in hydration products was higher.Therefore,cement-based materials with higher portlandite content exhibit weaker erosion resistance.Model-building concrete,with C-S-H gel and portlandite as primary hydration products,has greater erosion susceptibility than shotcrete with ettringite as main hydration product.Moreover,adding silicon-rich mineral admixtures can enhance the erosion resistance.This research offers theory and tech insights to boost cement-based material resistance against carbonated water erosion in karst tunnel engineering.
基金the Fundamental Research Funds for the Central Universities (Nos. 2024CDJXY0022023CDJYGRH-YB17+4 种基金2022CDJXY-025)the Venture & Innovation Support Program for Chongqing Overseas Returnees (No. cx2022061)the Natural Science Foundation of Chongqing (No. CSTB2022NSCQ-MSX1123)the Chongqing Talents: Exceptional Young Talents Project (No. cstc2021ycjh-bgzxm0067)the Hongshen Young Scholars Program from Chongqing University (No. 0247001104426) for financial support。
文摘The design and synthesis of a novel π-conjugated fiuorescent framework by external ligand-assisted C-H olefination of heterocycles with excellent regioselectivity and broad substrate scope are reported herein.These novel fiuorescent materials could present full-color-tunable emissions with large Stokes shifts. Furthermore, the protocol provides an opportunity to rapidly screen novel organic single-molecule whitelight materials with high fiuorescence quantum yields. The robust organic and low-cost white lightemitting diodes could rapidly be fabricated using the white-light-emitting material. Experimental data and theoretical calculations indicate that in the white-light dual emission the relatively short wavelength from high-lying singlet state emission and the relatively long wavelength from low-lying singlet state emission. The anti-Kasha dual-emission systems will provide a foundation for the development and application of organic single-molecule white light materials, effectively promoting the development and innovation of luminescent materials. In addition, this method demonstrated its potential application in the synthesis of new near-infrared(NIR) fiuorescence materials with large Stokes shifts based on the olefination of heterocycles.
基金supported by the Major Science and Technology Projects in Yunnan Province(Grant No.202402AF080005)National Natural Science Foundation of China(Grant Nos.52274408,22468029,52274412)+2 种基金Yunnan Fundamental Research Projects(Grant No.202201AW070014)the Program for Innovative Research Team in University of Ministry of Education of China(Grant No.IRT 17R48)the German Research Foundation(DFG,Project number 501766751).
文摘While silicon/carbon(Si/C)is considered one of the most promising anode materials for the next generation of high-energy lithium-ion batteries(LIBs),the industrialization of Si/C anodes is hampered by high-cost and low product yield.Herein,a high-yield strategy is developed in which photovoltaic waste silicon is converted to cost-effective graphitic Si/C composites(G-Si@C)for LIBs.The introduction of a binder improves the dispersion and compatibility of silicon and graphite,enhances particle sphericity,and significantly reduces the loss rate of the spray prilling process(from about 25%to 5%).As an LIB anode,the fabricated G-Si@C composites exhibit a capacity of 605 mAh g^(-1) after 1200 cycles.The cost of manufacturing Si/C anode materials has been reduced to approximately$7.47 kg^(-1),which is close to that of commercial graphite anode materials($5.0 kg^(-1)),and significantly lower than commercial Si/C materials(ca.$20.74 kg^(-1)).Moreover,the G-Si@C material provides approximately 81.0 Ah/$of capacity,which exceeds the current best commercial graphite anodes(70.0 Ah/$)and Si/C anodes(48.2 Ah/$).The successful implementation of this pathway will significantly promote the industrialization of high-energydensity Si/C anode materials.
基金financially supported by the National Natural Science Foundation of China(Nos.22302133 and 22405161)Central Guidance on Local Science and Technology Development Fund of Hebei Province,China(No.236Z4406G)+5 种基金the Natural Science Foundation of Hebei Education Department,China(No.BJ2025100)the Natural Science Foundation of Hebei Province,China(No.B2021210001)the Natural Science Foundation of Xinjiang Uygur Autonomous Region(No.2024D01A157)the Key R&D Plan of Karamay(No.2024zdyf0009)Karamay Innovation Environment Construction Plan(Innovative Talents)Project(No.2024hjcxrc0029)the Research Foundation of China University of Petroleum-Beijing at Karamay(No.XQZX20240023)
文摘Tin dioxide(SnO_(2))with a high theoretical specific capacity of 1494 mAh g^(-1)is a promising candidate anode material for lithium storage.However,the shortcomings of serious volume expansion and low conductivity limit its wide application.Herein,coaxial nano-multilayered C/SnO_(2)/TiO_(2)composites were fabricated via layerby-layer self-assembly of TiO_(2)and SnO_(2)-gel layers on the natural cellulose filter paper,followed by thermal treatment under a nitrogen atmosphere.Through engineering design of the assembly process,the optimal C/SinO_(2)/TiO_(2)composite features five alternating SnO_(2)and TiO_(2)nanolayers,with TiO_(2)as the outside shell(denoted as C/TSTST).This unique structure endows the C/TSTST with excellent structural stability and electrochemical kinetics,making it a high-performance anode for lithium-ion batteries(LIBs).The C/TSTST composite delivers a high reversible capacity of 676 mAh g^(-1)at 0.1 A g^(-1)after 200 cycles and retains a capacity of 504 mAh g^(-1)at 1.0 A g^(-1),which can be recovered to 781 mAh g^(-1)at 0.1 A g^(-1)The significantly enhanced electrochemical performance is attributed to the hierarchical hybrid structure,where the carbon core combined with coaxial TiO_(2)nanolayers serves as a structural scaffold,ameliorating volume change of SnO_(2)while creating abundant interfacial defects for enhanced lithium storage and rapid charge transport.These findings are further demonstrated by the density functional theory(DFT)calculations.This work provides an efficient strategy for designing coaxial nano-multilayered transition metal oxide-related electrode materials,offering new insights into high-performance LIBs anodes.
基金Supported by National Key Technology Research and Development Program(2012BAD40B02Yunnan Provincial Tobacco Company Plan Project(2012YN48)~~
文摘The oilseed cake, vetch, rapeseed straw, wheat straw and corn straw were buried in tobacco-planted soil. The decomposition rates, the variation of active organic C and N contents in the residues and the relationship between active organic C and N contents and decomposition rate were investigated. The results showed the decomposition rates of different organic materials were all high in the early period and then low in the late period. Among the organic materials, the decomposition rates ranked as oilseed cake 〉 vetch 〉 wheat straw and rapeseed straw 〉 corn straw. The decomposition rate was positively related to total N content （P〈0.01）, but was negatively related to the active organic C/N ratio （P〈0.01）. However, there was no significant relationship between decomposition ratio and active organic C content. With the proceeding of decomposition, the active organic C content and the total N content in rapeseed straw, vetch, wheat straw and corn straw all trended to increase, but the active organic C/N ratio trended to decrease. However, the variation of active organic C content, total N content and active organic C/N ratio in oilseed cake was on the contrary.
基金Project (0991025) supported by Natural Science Foundation of Guangxi, ChinaProject (51164007) supported by the National Natural Science Foundation of ChinaProject (201101ZD008) supported by Educational Commission of Guangxi, China
文摘The LiMnPO4/C composite material was synthesized via a sol-gel method based on the citric acid. The X-ray diffraction （XRD）, scanning electron microscopy （SEM） and electrochemical performance tests were adopted to characterize the properties of LiMnPO4/C. The XRD studies show that the pure olivine phase LiMnPO4 can be obtained at a low temperature of 500 °C. The SEM analyses illustrate that the citric acid used as the chelating reagent and carbon source can restrain the particle size of LiMnPO4/C well. The LiMnPO4/C sample synthesized at 500 °C for 10 h performs the highest initial discharge capacity of 122.6 mA-h/g, retaining 112.4 mA-h/g over 30 cycles at 0.05C rate. The citric acid based sol-gel method is favor to obtain the high electrochemical performance of LiMnPO4/C.
基金Project(2011FJ1005)supported by the Science and Technology Programs of Hunan Province,China
文摘Silicon/flake graphite/carbon （Si/FG/C） composites were synthesized with different dispersants via spray drying and subsequent pyrolysis, and effects of dispersants on the characteristics of the composites were investigated. The structure and properties of the composites were determined by X-ray diffractometry （XRD）, scanning electron microscopy （SEM） and electrochemical measurements. The results show that samples have silicon/flake graphite/amorphous carbon composite structure, good spherical appearances, and better electrochemical performance than pure nano-Si and FG/C composites. Compared with the Si/FG/C composite using washing powder as dispersant, the Si/FG/C composite using sodium dodecyl benzene sulfonate （SDBS） as dispersant has better electrochemical performance with a reversible capacity of 602.68 mA·h/g, and a capacity retention ratio of 91.58 % after 20 cycles.
基金financial support granted by the National Natural Science Foundation of China (No. 22402225)the Gusu Innovation and Entrepreneurship Leading Talent Plan(No. ZXL2023193)+2 种基金the Sinano Talents Plan (No. 2022000175)the Guangdong Basic and Applied Basic Research Foundation (No.2023A1515111133)the ANSO Scholarship for Young Talents
文摘Inorganic materials can solve transportable and on-site hydrolytic hydrogen generation issues.CaH_(2)/(Al/Si)composites are preferable due to their notable chemical properties.However,these composites require pretreatments,an inert environment,and long hours of physical ball milling for high homogeneity and synergistic effects.CaH_(2)also inhibits the hydrolysis reaction by forming its products on the Al/Si surface,which hinders the direct utilization of composites.This work represents the first investigation of NaH-CaH_(2)(Al/Si)fuel composites,which greatly overcome these limitations and can be directly used for on-site hydrogen generation and proton exchange membrane(PEM)fuel cells.The NaH-CaH_(2)(Al/Si)fuel composites were prepared by using a straightforward mixing method with variable composition ratios,showing high H_(2)yield and fuel cell(FC)performance.NaH addition provides the bridge effect,which opens up a new way to enable efficient hydrolysis and greatly enhances the hydrolysis activity of CaH_(2)/(Al/Si)composites.The novel fuel composites(NaH-CaH_(2)/Al)have extraordinary FC performance and a 0.42 W/cm2 peak power density greater than commercial hydrogen generators.It provides high H_(2)yield 84.4%for NaH-CaH_(2)/Al and 82%for NaH-CaH_(2)/Si compared to NaOH-CaH_(2)(Al/Si),NaCl-CaH_(2)(Al/Si),and KCl-CaH_(2)(Al/Si)composites.The NaH bridge effect hinders the direct water contact and stops the formation of Ca(OH)2 around Al/Si,which provides adequate pathways for the CaH_(2)(Al/Si)hydrolysis.The impressive capabilities of novel fuel composites are anticipated to offer practical uses in fuel cells,automobile applications,and portable/on-board H_(2)generation.
基金Project(2013AA050901)supported by the National High-tech Research and Development Program of China
文摘In order to enhance electrochemical properties of LiFePO4 （LFP） cathode materials, spherical porous nano/micro structured LFP/C cathode materials were synthesized by spray drying, followed by calcination. The results show that the spherical precursors with the sizes of 0.5-5 μm can be completely converted to LFP/C when the calcination temperature is higher than 500 ℃. The LFP/C microspheres obtained at calcination temperature of 700 ℃ are composed of numerous particles with sizes of -20 nm, and have well-developed interconnected pore structure and large specific surface area of 28.77 mE/g. The specific discharge capacities of the LFP/C obtained at 700 ℃ are 162.43, 154.35 and 144.03 mA.h/g at 0.5C, 1C and 2C, respectively. Meanwhile, the capacity retentions can reach up to 100% after 50 cycles. The improved electrochemical properties of the materials are ascribed to a small Li＋ diffusion resistance and special structure of LFP/C microspheres.
基金supported financially by the National Natural Science Foundation of China (Nos. U1435206 and 51672064)the Beijing Municipal Science & Technology Commission (No. D161100002416001)
文摘Researching for interphase materials that can protect SiC fibers from oxygen and water vapor attacks has become one of the most important issues for the applications of SiC_f/SiC composites in high-temperature combustion environment. However, such kinds of interphase materials are not available yet. Herein,we report theoretically predicted properties of two promising interphase materials Y_5Si_3 C and Y_3Si_2C_2.Although crystallizing in different structures, they share the common features of layered structure,anisotropic chemical bonding, anisotropic electrical and mechanical properties, and low shear deformation resistance. The bulk moduli for Y_5Si_3C and Y_3Si_2C_2 are 78 and 93 GPa, respectively; while their shear moduli are 52 and 50GPa, respectively. The maximum to minimum Young's modulus ratios are1.44 for Y_5Si_3C and 3.27 for Y_3Si_2C_2. Based on the low shear deformation resistance and low Pugh's ratios(G/B = 0.666 forY_5Si_3C and 0.537 for Y_3Si_2C_2; G: shear modulus; B: bulk modulus), they are predicted as damage tolerant and soft ceramics with predicted Vickers hardness of 9.6 and 6.9 GPa, respectively.The cleavage plane and possible slip systems are(000 l) and(0001)[1120] and(1010)[0001] forY_5Si_3C,and those for Y_3Si_2C_2 are {h00} and(010)[101]. Since the oxidation products are water-vapor resistant Y2 Si2 O7, Y2 SiO5 and/or Y_2 O_3 upon oxidation, and the volume expansions are ca 140% and ca 26% for Y_5Si_3C and Y_3Si_2C_2, they are expected to seal the interfacial cracks in SiC_f/SiC composites. The unique combination of easy cleavage, low shear deformation resistance, volume expansions upon oxidation, and the resistance of the oxidation products to water vapor attack warrant them promising as interphase materials of SiC_f/SiC composites for water-vapor laden environment applications.
基金This work was financially supported by the National Natural Science Foundation of China (No.50134020)
文摘Spherical LiFePO4 and LiFePO4/C composite powders for lithium ion batteries were synthesized by a novel processing route of co-precipitation and subsequent calcinations in a nitrogen and hydrogen atmosphere. The precursors of LiFePO4, LiFePO4/C composite and the resultant products were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), and the electrochemical performances were investigated by galvanostatic charge and discharge tests. The precursors composed of amorphous Fe3(PO4)2·xH2O and crystalline Li3PO4 obtained in the co-precipitation processing have a sphere-like morphology. The spherical LiFePO4 derived from the calcinations of the precursor at 700 ℃ for 10 h in a reduction atmosphere shows a discharge capacity of 119 mAh·g-1 at the C/10 rate, while the LiFePO4/C composite with 10wt.% carbon addition exhibits a discharge capacity of 140 mAh·g-1. The electrochemical performances indicate that the LiFePO4/C composite has a higher specific capacity and a more stable cycling performance than the bare olivine LiFePO4 due to the carbon addition enhancing the electronic conductivity.
基金supported by the National Basic Research Program of China(Grant No.2014CB643702)the National Natural Science Foundation of China(Grant No.51590880)+1 种基金the Knowledge Innovation Project of the Chinese Academy of Sciences(Grant No.KJZD-EW-M05)the National Key Research and Development Program of China(Grant No.2016YFB0700903)
文摘Data-mining techniques using machine learning are powerful and efficient for materials design, possessing great potential for discovering new materials with good characteristics. Here, this technique has been used on composition design for La（Fe,Si/Al）（13）-based materials, which are regarded as one of the most promising magnetic refrigerants in practice. Three prediction models are built by using a machine learning algorithm called gradient boosting regression tree（GBRT） to essentially find the correlation between the Curie temperature（TC）, maximum value of magnetic entropy change（（？SM）（max））,and chemical composition, all of which yield high accuracy in the prediction of TC and（？SM）（max）. The performance metric coefficient scores of determination（R^2） for the three models are 0.96, 0.87, and 0.91. These results suggest that all of the models are well-developed predictive models on the challenging issue of generalization ability for untrained data, which can not only provide us with suggestions for real experiments but also help us gain physical insights to find proper composition for further magnetic refrigeration applications.
基金National Natural Science Foundation of China with Grant No.21905304Natural Science Foundation of Shandong Province(No.ZR2019BEM031)the Fundamental Research Funds for the Central Universities(Nos.18CX02158A and 19CX05001A).
文摘Ti3C2Tx,a novel two-dimensional layer material,is widely used as electrode materials of supercapacitor due to its good metal conductivity,redox reaction active surface,and so on.However,there are many challenges to be addressed which impede Ti3C2Tx obtaining the ideal specific capacitance,such as restacking,re-crushing,and oxidation of titanium.Recently,many advances have been proposed to enhance capacitance performance of Ti3C2Tx.In this review,recent strategies for improving specific capacitance are summarized and compared,for example,film formation,surface modification,and composite method.Furthermore,in order to comprehend the mechanism of those efforts,this review analyzes the energy storage performance in different electrolytes and influencing factors.This review is expected to predict redouble research direction of Ti3C2Tx materials in supercapacitors.
