Cation-disordered rocksalt oxides(DRX)have been identified as promising cathode materials for high energy density applications owing to their variable elemental composition and cationic-anionic redox activity.However,...Cation-disordered rocksalt oxides(DRX)have been identified as promising cathode materials for high energy density applications owing to their variable elemental composition and cationic-anionic redox activity.However,their practical implementation has been impeded by unwanted phenomena such as irrepressible transition metal migration/dissolution and O_(2)/CO_(2)evolution,which arise due to parasitic reactions and densification-degradation mechanisms during extended cycling.To address these issues,a micron-sized DRX cathode Li_(1.2)Ni_(1/3)Ti_(1/3)W_(2/15)O_(1.85)F_(0.15)(SLNTWOF)with F substitution and ultrathin LiF coating layer is developed by alcohols assisted sol-gel method.Within this fluorination-induced integrated structure design(FISD)strategy,in-situ F substitution modifies the activity/reversibility of the cationic-anionic redox reaction,while the ultrathin LiF coating and single-crystal structure synergistically mitigate the cathode/electrolyte parasitic reaction and densification-degradation mechanism.Attributed to the multiple modifications and size effect in the FISD strategy,the SLNTWOF sample exhibits reversible cationic-anionic redox chemistry with a meliorated reversible capacity of 290.3 mA h g^(-1)at 0.05C(1C=200 mA g^(-1)),improved cycling stability of 78.5%capacity retention after 50 cycles at 0.5 C,and modified rate capability of 102.8 mA h g^(-1)at 2 C.This work reveals that the synergistic effects between bulk structure modification,surface regulation,and engineering particle size can effectively modulate the distribution and evolution of cationic-anionic redox activities in DRX cathodes.展开更多
The lattice oxygen oxidation mechanism(LOM)provides an efficient pathway for accelerating the oxygen evolution reaction(OER)in certain electrocatalysts by activating and involving lattice oxygen in the catalytic OER p...The lattice oxygen oxidation mechanism(LOM)provides an efficient pathway for accelerating the oxygen evolution reaction(OER)in certain electrocatalysts by activating and involving lattice oxygen in the catalytic OER process.We investigated the potential of disordered rocksalts as catalysts for accelerating the OER through the LOM process,leveraging their unique metastable Li-O-Li bond states.Theoretical calculations were employed to predict the catalytic pathways and activities of disordered rocksalts(DRX),such as Li_(1.2)Co_(0.4)Ti_(0.5)O_(2)(LCTO).The results revealed that benefiting from the unhybridized Li-O electronic orbitals and the resulting metastable states of Li-O-Li bonds in DRX,LCTO exhibited a typical LOM pathway,and the lattice oxygen was easily activated and participated in the OER.The experimental results showed that LCTO exhibited a remarkable pH-dependent OER activity through the LOM pathway,with an overpotential of 241 mV at a current density of 10 mA/cm^(2),and excellent long-term stability.This work provides a novel chemical space for designing highly active and stable OER electrocatalysts by leveraging the LOM reaction pathway.展开更多
The reconstruction during oxygen evolution reaction (OER) significantly affects the electronic and local geometry structure of metal sites in electrocatalyst.Compared with well-investigated cobalt-based materials,the ...The reconstruction during oxygen evolution reaction (OER) significantly affects the electronic and local geometry structure of metal sites in electrocatalyst.Compared with well-investigated cobalt-based materials,the reconstruction of rocksalt CoO with purely Co^(2+) in octahedral (Oh) coordination has not been revealed in detail.Herein,monolayer Co O supported on reduced graphene oxide (r GO) was synthesized via a one-pot hydrothermal strategy with calcinating in Ar atmosphere.The structure evolution of twodimension (2D) Co O/r GO during OER was revealed by in situ X-ray absorption spectroscopy (XAS).The transition from Co O toward Co3O_(4) already occurred at open circuit potential,further enhanced at 1.23 V (vs.RHE).The Co Ox(OH)ywas determined as the active phase at 1.53 V,displaying a tetrahedral Co coordination defective spinel Co_(3)O_(4) with the Co-O shell that featured the (oxy)hydroxide,not the standard Co OOH.After OER,the irreversible transition from CoO to Co_(3)O_(4) was observed.In contrast,in situ Raman spectra revealed a reversible amorphization process on Co_(3)O_(4)/r GO under operation conditions.Furthermore,this study indicated that the reconstruction behavior could be more effectively revealed by XAS using 2D materials.展开更多
The structural, electronic and optical properties of rocksalt CdO have been studied using the plane-wave-based pseudo-potential density functional theory within generalized gradient approximation. The calculated latti...The structural, electronic and optical properties of rocksalt CdO have been studied using the plane-wave-based pseudo-potential density functional theory within generalized gradient approximation. The calculated lattice parameters are in agreement with previous experimental work. The band structure, density of states, and Mulliken charge population are obtained, which indicates that rocksalt CdO having the properties of a halfmetal due to an indirect band gap of -0.51eV. The mechanical properties show that rocksalt CdO is mechanically stable, isotropic and malleable. Significantly, we propose a correct value for ε1(0) of about 4.75, which offers theoretical data for the design and application for rocksalt CdO in optoelectronic materials.展开更多
高熵材料可以在单一晶相中引入五种或五种以上元素以优化电子结构和配位环境,可作为一类新兴的电催化剂.本文制备了一种岩盐型高熵氧化物Mg_(0.2)Co_(0.2)Ni_(0.2)Cu_(0.2)Zn_(0.2)O(HEO)用于催化氧析出反应(OER).由于相邻的不同金属离...高熵材料可以在单一晶相中引入五种或五种以上元素以优化电子结构和配位环境,可作为一类新兴的电催化剂.本文制备了一种岩盐型高熵氧化物Mg_(0.2)Co_(0.2)Ni_(0.2)Cu_(0.2)Zn_(0.2)O(HEO)用于催化氧析出反应(OER).由于相邻的不同金属离子晶格失配,所制备的HEO具有丰富的缺陷.此外,电负性更小的Mg和Zn元素的存在使Co/Ni‒O共价性增强.得益于此,HEO在碱性条件下展现出优异的OER本征催化活性,其转换频率(TOF)在1.65 V时分别达到CoO和NiO的15和84倍.本文探究了HEO电催化性能提升机制,论证了通过合理添加低成本和低电负性元素的高熵策略在发展高效氧电催化剂方面的潜能.采用静电纺丝和热处理的方法制备了含有五种金属元素的HEO,X射线衍射(XRD)结果表明其为岩盐型晶体结构.X射线能量色散谱(EDS)和电感耦合等离子体发射光谱(ICP-OES)分析表明五种元素接近等摩尔比,且均匀分布.通过高分辨透射电子显微镜(HRTEM)发现HEO晶格中含有大量缺陷;同步辐射扩展X射线吸收精细结构(EXAFS)谱拟合数据显示HEO中Co和Ni的配位数相比CoO和NiO均有所降低,证实了缺陷的存在.此外,O 1s的X射线光电子能谱(XPS)和电子顺磁共振谱(EPR)进一步证明HEO含有大量氧缺陷.缺陷结构有利于配位不饱和的活性位点充分暴露,促进反应中间体的吸附,从而提升电催化活性.通过X射线吸收近边结构(XANES)谱分析了HEO中Co和Ni的电子结构信息.结果表明,相比CoO和NiO,HEO中Co和Ni的氧化态更低,因为HEO中电负性更低的Mg和Zn可以向O转移更多电子,使相邻的Co和Ni贡献更少电子.更高的电荷密度说明Co/Ni‒O键的共价性增强,与傅里叶变换的EXAFS谱中Co/Ni‒O键的键长变短相吻合.此外,Co和Ni2p的XPS结果表明,HEO表面Co(Ⅱ)和Ni(Ⅱ)成分占比较CoO和NiO更高,也证明HEO中Co/Ni‒O键具有更高的共价性.在1 M KOH中,HEO展现出优越的OER电催化性能,其达到10 mA cm^(−2)电流密度时过电位为360 mV,明显小于CoO和NiO,且与大多数文献报道的高熵电催化剂相当.此外,其Tafel斜率、质量比活性、单位面积活性和TOF均显著优于CoO和NiO,而采用相同方法制备的Co_(0.5)Ni_(0.5)O则性能较差.据此可以推测HEO电催化性能提升的主要原因在于:高熵策略可以调控活性金属的电子结构,通过引入低电负性元素增强Co/Ni‒O键的共价性,提升其本征催化活性;高熵体系中不同金属元素的尺寸差异导致大量缺陷产生,调控了活性位点的配位环境,从而促进活性位点暴露,提升催化性能.展开更多
The constitutive model Hou/Lux,based on continuum damage mechanics and on the material model Lubby2 is presented and the damage,the healing of damage,the tertiary creep and the creep rupture of rock salt described. An...The constitutive model Hou/Lux,based on continuum damage mechanics and on the material model Lubby2 is presented and the damage,the healing of damage,the tertiary creep and the creep rupture of rock salt described. An application shows how phenomena observed in laboratory tests on axially perforated cylinder sample, such as softening, dilatancy, spalling and radial deformation into the axial bore as well as spalling can be numerically simulated with the model Hou/Lux. Furthermore,it is then evaluated against the measured permeability and stress profiles of a 37-year-old drift at the Sondershausen minein,Germany. Satisfactory agreement is obtained between the calculated and measured data.展开更多
A thermo-plastic/viscoplastic damage coupled model was formulated to describe the time independent and time dependent behaviors of geomaterials under temperature effect. The plastic strain was divided into instantaneo...A thermo-plastic/viscoplastic damage coupled model was formulated to describe the time independent and time dependent behaviors of geomaterials under temperature effect. The plastic strain was divided into instantaneous plastic strain and creep plastic strain. To take temperature effect into acconnt, a temperature variable was introduced into the instantaneous and creep plastic behavior descriptions and damage characterization, and a linear thermal expansion law was used in constitutive equation formulation. According to the mechanical behavior of rock salt, a specific model was proposed based on the previous model and applied to Avery rock salt, in which the numerical results obtained from our model had a good agreement with the data from experiments.展开更多
基金supported by the National Key R&D Program of China(2021YFB2401800)the National Natural Science Foundation of China(22179008,21875022)+2 种基金the Natural Science Foundation of Chongqing,China(cstc2020jcyj-msxmX0589,cstc2020jcyjmsxmX0654)the support from Beijing Institute of Technology Research Fund Program for Young Scholarsthe 4B7B beamlines radiation equipment of Beijing Synchrotron Radiation Facility(2021-BEPC-PT-005924,2021-BEPC-PT-005967)。
文摘Cation-disordered rocksalt oxides(DRX)have been identified as promising cathode materials for high energy density applications owing to their variable elemental composition and cationic-anionic redox activity.However,their practical implementation has been impeded by unwanted phenomena such as irrepressible transition metal migration/dissolution and O_(2)/CO_(2)evolution,which arise due to parasitic reactions and densification-degradation mechanisms during extended cycling.To address these issues,a micron-sized DRX cathode Li_(1.2)Ni_(1/3)Ti_(1/3)W_(2/15)O_(1.85)F_(0.15)(SLNTWOF)with F substitution and ultrathin LiF coating layer is developed by alcohols assisted sol-gel method.Within this fluorination-induced integrated structure design(FISD)strategy,in-situ F substitution modifies the activity/reversibility of the cationic-anionic redox reaction,while the ultrathin LiF coating and single-crystal structure synergistically mitigate the cathode/electrolyte parasitic reaction and densification-degradation mechanism.Attributed to the multiple modifications and size effect in the FISD strategy,the SLNTWOF sample exhibits reversible cationic-anionic redox chemistry with a meliorated reversible capacity of 290.3 mA h g^(-1)at 0.05C(1C=200 mA g^(-1)),improved cycling stability of 78.5%capacity retention after 50 cycles at 0.5 C,and modified rate capability of 102.8 mA h g^(-1)at 2 C.This work reveals that the synergistic effects between bulk structure modification,surface regulation,and engineering particle size can effectively modulate the distribution and evolution of cationic-anionic redox activities in DRX cathodes.
基金supported by the National Natural Science Foundation of China(Nos.52177220,52231008)Key Research and Development Program of Hainan Province(ZDYF2022GXJS006)。
文摘The lattice oxygen oxidation mechanism(LOM)provides an efficient pathway for accelerating the oxygen evolution reaction(OER)in certain electrocatalysts by activating and involving lattice oxygen in the catalytic OER process.We investigated the potential of disordered rocksalts as catalysts for accelerating the OER through the LOM process,leveraging their unique metastable Li-O-Li bond states.Theoretical calculations were employed to predict the catalytic pathways and activities of disordered rocksalts(DRX),such as Li_(1.2)Co_(0.4)Ti_(0.5)O_(2)(LCTO).The results revealed that benefiting from the unhybridized Li-O electronic orbitals and the resulting metastable states of Li-O-Li bonds in DRX,LCTO exhibited a typical LOM pathway,and the lattice oxygen was easily activated and participated in the OER.The experimental results showed that LCTO exhibited a remarkable pH-dependent OER activity through the LOM pathway,with an overpotential of 241 mV at a current density of 10 mA/cm^(2),and excellent long-term stability.This work provides a novel chemical space for designing highly active and stable OER electrocatalysts by leveraging the LOM reaction pathway.
基金supported by the National Natural Science Foundation of China(21872093)the National Key Research and Development Program of China(2018YFB1502001)funding support from the Center of Hydrogen Science,Shanghai Jiao Tong University,China。
文摘The reconstruction during oxygen evolution reaction (OER) significantly affects the electronic and local geometry structure of metal sites in electrocatalyst.Compared with well-investigated cobalt-based materials,the reconstruction of rocksalt CoO with purely Co^(2+) in octahedral (Oh) coordination has not been revealed in detail.Herein,monolayer Co O supported on reduced graphene oxide (r GO) was synthesized via a one-pot hydrothermal strategy with calcinating in Ar atmosphere.The structure evolution of twodimension (2D) Co O/r GO during OER was revealed by in situ X-ray absorption spectroscopy (XAS).The transition from Co O toward Co3O_(4) already occurred at open circuit potential,further enhanced at 1.23 V (vs.RHE).The Co Ox(OH)ywas determined as the active phase at 1.53 V,displaying a tetrahedral Co coordination defective spinel Co_(3)O_(4) with the Co-O shell that featured the (oxy)hydroxide,not the standard Co OOH.After OER,the irreversible transition from CoO to Co_(3)O_(4) was observed.In contrast,in situ Raman spectra revealed a reversible amorphization process on Co_(3)O_(4)/r GO under operation conditions.Furthermore,this study indicated that the reconstruction behavior could be more effectively revealed by XAS using 2D materials.
文摘The structural, electronic and optical properties of rocksalt CdO have been studied using the plane-wave-based pseudo-potential density functional theory within generalized gradient approximation. The calculated lattice parameters are in agreement with previous experimental work. The band structure, density of states, and Mulliken charge population are obtained, which indicates that rocksalt CdO having the properties of a halfmetal due to an indirect band gap of -0.51eV. The mechanical properties show that rocksalt CdO is mechanically stable, isotropic and malleable. Significantly, we propose a correct value for ε1(0) of about 4.75, which offers theoretical data for the design and application for rocksalt CdO in optoelectronic materials.
文摘高熵材料可以在单一晶相中引入五种或五种以上元素以优化电子结构和配位环境,可作为一类新兴的电催化剂.本文制备了一种岩盐型高熵氧化物Mg_(0.2)Co_(0.2)Ni_(0.2)Cu_(0.2)Zn_(0.2)O(HEO)用于催化氧析出反应(OER).由于相邻的不同金属离子晶格失配,所制备的HEO具有丰富的缺陷.此外,电负性更小的Mg和Zn元素的存在使Co/Ni‒O共价性增强.得益于此,HEO在碱性条件下展现出优异的OER本征催化活性,其转换频率(TOF)在1.65 V时分别达到CoO和NiO的15和84倍.本文探究了HEO电催化性能提升机制,论证了通过合理添加低成本和低电负性元素的高熵策略在发展高效氧电催化剂方面的潜能.采用静电纺丝和热处理的方法制备了含有五种金属元素的HEO,X射线衍射(XRD)结果表明其为岩盐型晶体结构.X射线能量色散谱(EDS)和电感耦合等离子体发射光谱(ICP-OES)分析表明五种元素接近等摩尔比,且均匀分布.通过高分辨透射电子显微镜(HRTEM)发现HEO晶格中含有大量缺陷;同步辐射扩展X射线吸收精细结构(EXAFS)谱拟合数据显示HEO中Co和Ni的配位数相比CoO和NiO均有所降低,证实了缺陷的存在.此外,O 1s的X射线光电子能谱(XPS)和电子顺磁共振谱(EPR)进一步证明HEO含有大量氧缺陷.缺陷结构有利于配位不饱和的活性位点充分暴露,促进反应中间体的吸附,从而提升电催化活性.通过X射线吸收近边结构(XANES)谱分析了HEO中Co和Ni的电子结构信息.结果表明,相比CoO和NiO,HEO中Co和Ni的氧化态更低,因为HEO中电负性更低的Mg和Zn可以向O转移更多电子,使相邻的Co和Ni贡献更少电子.更高的电荷密度说明Co/Ni‒O键的共价性增强,与傅里叶变换的EXAFS谱中Co/Ni‒O键的键长变短相吻合.此外,Co和Ni2p的XPS结果表明,HEO表面Co(Ⅱ)和Ni(Ⅱ)成分占比较CoO和NiO更高,也证明HEO中Co/Ni‒O键具有更高的共价性.在1 M KOH中,HEO展现出优越的OER电催化性能,其达到10 mA cm^(−2)电流密度时过电位为360 mV,明显小于CoO和NiO,且与大多数文献报道的高熵电催化剂相当.此外,其Tafel斜率、质量比活性、单位面积活性和TOF均显著优于CoO和NiO,而采用相同方法制备的Co_(0.5)Ni_(0.5)O则性能较差.据此可以推测HEO电催化性能提升的主要原因在于:高熵策略可以调控活性金属的电子结构,通过引入低电负性元素增强Co/Ni‒O键的共价性,提升其本征催化活性;高熵体系中不同金属元素的尺寸差异导致大量缺陷产生,调控了活性位点的配位环境,从而促进活性位点暴露,提升催化性能.
文摘The constitutive model Hou/Lux,based on continuum damage mechanics and on the material model Lubby2 is presented and the damage,the healing of damage,the tertiary creep and the creep rupture of rock salt described. An application shows how phenomena observed in laboratory tests on axially perforated cylinder sample, such as softening, dilatancy, spalling and radial deformation into the axial bore as well as spalling can be numerically simulated with the model Hou/Lux. Furthermore,it is then evaluated against the measured permeability and stress profiles of a 37-year-old drift at the Sondershausen minein,Germany. Satisfactory agreement is obtained between the calculated and measured data.
基金Project supported by the National Natural Science Foundation of China(NSFC) (Nos. 10772190,50979104 and 51009132)
文摘A thermo-plastic/viscoplastic damage coupled model was formulated to describe the time independent and time dependent behaviors of geomaterials under temperature effect. The plastic strain was divided into instantaneous plastic strain and creep plastic strain. To take temperature effect into acconnt, a temperature variable was introduced into the instantaneous and creep plastic behavior descriptions and damage characterization, and a linear thermal expansion law was used in constitutive equation formulation. According to the mechanical behavior of rock salt, a specific model was proposed based on the previous model and applied to Avery rock salt, in which the numerical results obtained from our model had a good agreement with the data from experiments.