Bimetallic metal organic framework(MOF)as a precursor to prepare catalysts with bifunctional catalytic activity of oxygen evolution reaction(OER)and hydrogen evolution reaction(HER)attracts more and more attention.Her...Bimetallic metal organic framework(MOF)as a precursor to prepare catalysts with bifunctional catalytic activity of oxygen evolution reaction(OER)and hydrogen evolution reaction(HER)attracts more and more attention.Herein,hollow oxygen deficiency-enriched NiFe_(2)O_(4) is synthesized by pyrolytic FeNi bimetallic MOF.The defects of rGO during carbonization can act as nucleation sites for FeNi particles.After nucleation and N doping,the FeNi particles were served as catalysts for the deposition of dissolved carbon in the defects of the N/rGO.These deposited carbon,like a bridge,connect N/rGO and hollow oxygen deficiency-enriched NiFe_(2)O_(4) together,which giving full play to the advantages of N/rGO in fast electron transfer,thereby improving its catalytic activity.The resultant NiFe_(2)O_(4)@N/rGO-800 exhibits a low overpotential of 252 mV at 20 mA cm^(-2) for OER and 157 mV at 10 mA cm^(-2) for HER in 1 M KOH,respectively.When used as bifunctional electrodes for overall water splitting,it also shows low cell voltage of 1.60 V and 1.67 V at 10 and 20 mA cm^(-2),respectively.展开更多
Due to unique electrical properties and high catalytic efficiency,transition metal nitrogen-codoped car-bide(TM-N-C)has attracted tremendous interest as a multifunctional electrocatalyst for water splitting.Unlike tra...Due to unique electrical properties and high catalytic efficiency,transition metal nitrogen-codoped car-bide(TM-N-C)has attracted tremendous interest as a multifunctional electrocatalyst for water splitting.Unlike traditional single-source modification,herein a novel pomegranate-like high-entropy(HE)elec-trocatalyst of Ni_(3)ZnC_(0.7)decorated with homogeneous multimetal(Fe,Co,Cu,and Ni)nitrogen-codoped carbon matrix(Ni_(3)ZnC_(0.7)@CoNiCuFe-NC)is reported.It can be implemented by the simple thermal an-nealing method of multimetal codoped zeolitic imidazolate framework(ZIF).Benefiting from the syn-ergistic effects of plentiful TM-N-C species,template effect of ZIF and distinct nanoporous structure,HE electrocatalyst Ni_(3)ZnC_(0.7)@CoNiCuFe-NC exhibits outstanding electrocatalytic performance.When ap-plied in strong alkaline electrolyte(1.0 M KOH),the overpotentials of Ni_(3)ZnC_(0.7)@CoNiCuFe-NC present as low as 202 and 97 mV for oxygen evolution reaction(OER)and hydrogen evolution reaction(HER)at 10 mA cm^(−2)current density.Surprisingly as a bifunctional electrode,it can achieve the low cell voltage of 1.53 V at 10 mA cm^(−2)current density for overall water splitting,which is comparable to conventional IrO_(2)||Pt/C electrode and superior to the recently reported analogous bifunctional catalysts.Thus,the work proposes the direction for the rational design of homogeneous distribution of TM-N-C material for water splitting in the green hydrogen energy industry.展开更多
The aqueous rechargeable Zn-ion batteries based on the safe,low cost and environmental benignity aqueous electrolytes are one of the most compelling candidates for large scale energy storage applications.However,pursu...The aqueous rechargeable Zn-ion batteries based on the safe,low cost and environmental benignity aqueous electrolytes are one of the most compelling candidates for large scale energy storage applications.However,pursuing suitable insertion materials may be a great challenge due to the strong electrostatic interaction between Zn^(^(2+))and cathode materials.Hence,a novel NaV_(6)O_(15)/V_(2)O_(5) skin-core heterostructure nanowire is reported via a one-step hydrothermal method and subsequent calcination for high-stable aqueous Zn-ion batteries(ZIBs).The NaV_(6)O_(15)/V_(2)O_(5) cathode delivers high specific capacity of 390 m Ah/g at 0.3 A/g and outstanding cycling stability of 267 m Ah/g at 5 A/g with high capacity retention over 92.3%after 3000 cycles.The superior electrochemical performances are attributed to the synergistic effect of skin-core heterostructured NaV_(6)O_(15)/V_(2)O_(5),in which the sheath of NaV_(6)O_(15) possesses high stability and conductivity,and the V_(2)O_(5) endows high specific capacity.Besides,the heterojunction structure not only accelerates intercalation kinetics of Zn^(2+)transport but also further consolidates the stability of the layers of V_(2)O_(5) during the cyclic process.This work provides a new perspective in developing feasible insertion materials for rechargeable aqueous ZIBs.展开更多
Single crystals subjected to shock compression exhibit responses with distinct two-wave structures for certain crystal orientations.However,little is known to date regarding how the shock response depends on crystal o...Single crystals subjected to shock compression exhibit responses with distinct two-wave structures for certain crystal orientations.However,little is known to date regarding how the shock response depends on crystal orientation,and especially why the two-wave structure depends on the crystal orientation.In this work,molecular dynamics simulations of shock compressions in copper single crystals are performed to investigate the orientation dependence of shock responses and the corresponding deformation mechanisms.Four copper single crystals with[001],[011],[012],and[123]crystal orientations along the depth direction are investigated.The[011],[012],and[123]crystal orientations of copper single crystals show distinct two-wave structures in their shock responses,while such a two-wave structure in the shock response is not seen for those orientations having a[001]crystal orientation.The potential causes are analyzed by considering the propagation velocities of both elastic and plastic waves.We develop a technique for identifying twin structures in face-centered cubic crystals and this technique can effectively identify the twin structure.The morphology of shock-induced defects(e.g.,dislocations and twins)shows the significant dependence of crystal orientation and the mechanisms behind these are discussed in detail.Finally,the Johnson-Cook constitutive model describing dynamic deformations at high temperatures and high strain rates is used to analyze the relationships between the shock responses and microscopic defects.The predictions of the Johnson-Cook constitutive model are consistent with the results of the molecular dynamics simulations.展开更多
In this paper,numerical investigation of hypersonic gas flow over two typical gap-cavity structures is carried out using all-speed preconditioned density-based solver.Such structures filled with porous seal in the gap...In this paper,numerical investigation of hypersonic gas flow over two typical gap-cavity structures is carried out using all-speed preconditioned density-based solver.Such structures filled with porous seal in the gap are often present at the joint locations of control surfaces of the hypersonic vehicles.Single-domain approach is adopted to integrate the governing equations for both porous and fluid regions.The basic thermal invasion characteristic is first illustrated using the maze gap-cavity structure without sealing.Then,the influence of seal filling depth on the thermal invasion characteristic is investigated for the structure with sealing.Finally,a comparison of thermal invasion characteristics between maze and straight gap-cavity structures is performed to examine the influence of gap bending.Results show that the main source of hot airflow invading into the gap is from the millimeter scale gas layer within the boundary layer.And the invasion characteristic presents approximate stationary behavior.A primary vortex occurs in the gap adjacent to the leeward wall,which is ascribed to the impinging effect between the separate boundary flow and the windward wall.This effect is also the main driving force of thermal invasion.A treatment of filling the seal in certain depth inside the gap can significantly reduce the thermal load of seal and maintain an acceptable level of the invading mass flow rate.Additionally,it is found that the gap bending exerts a limited block effect on the thermal invasion without sealing,and this effect can be ignored with sealing.These results can provide a reference for optimizing the seal gap-cavity structure configuration.展开更多
The interactions between the moving dislocation within matrix channel and the interfacial misfit dislocation networks on the two-phase interfaces in Ni-based single crystal superalloys are studied carefully via atomic...The interactions between the moving dislocation within matrix channel and the interfacial misfit dislocation networks on the two-phase interfaces in Ni-based single crystal superalloys are studied carefully via atomic modeling, with special focus on the factors influ- encing the critical bowing stress of moving dislocations in the matrix channel. The results show that the moving matrix dislocation type and its position with respect to the interfacial misfit dislocation segments have considerable influences on the interactions. If the moving matrix dislocation is pure screw, it reacts with the interracial misfit dislocation segments toward dislocation linear energy reduction, which decreases the critical bowing stress of screw dislocation due to dislocation linear energy release during the dislocation reactions. If the moving matrix dislocation is of 60^-mixed type, it is obstructed by the interaction between the mixed matrix dislocations and the misfit interfacial dislocation segments. As a result, the critical bowing stress increases significantly because extra interactive energy needs to be overcome. These two different effects on the critical bowing stress become in- creasingly significant when the moving matrix dislocation is very close to the interracial misfit dislocation segments. In addition, the matrix channel width also has a significant influence on the critical bowing stress, i.e. the narrower the matrix channel is, the higher the critical bowing stress is. The classical Orowan formula is modified to predict these effects on the critical bowing stress of moving matrix dislocation, which is in good agreement with the computational results.展开更多
The hydrogen effect on the nucleation and motion of dislocations in single-crystal bcc Fe with(110)surface was investigated by both nanoindentation experiments and discrete dislocation dynamics(DDD)simulation.The resu...The hydrogen effect on the nucleation and motion of dislocations in single-crystal bcc Fe with(110)surface was investigated by both nanoindentation experiments and discrete dislocation dynamics(DDD)simulation.The results of nanoindentation experiments showed that the pop-in load decreased evidently for the electrochemical hydrogen charging specimen,indicating that the dislocation nucleation strength might be reduced by hydrogen.In addition,the decrease of hardness due to hydrogen charging was also captured,implying that the dislocation motion might be promoted by hydrogen.By incorporating the effect of hydrogen on dislocation core energy,a DDD model was specifically proposed to investigate the influence of hydrogen on dislocation nucleation and motion.The results of DDD simulation revealed that under the effect of hydrogen,the dislocation nucleation strength is decreased and the motion of dislocation is promoted.展开更多
基金financially supported by the National Natural Science Foundation of China(Nos.21878231,21676202 and 51603145)Natural Science Foundation of Tianjin(Nos.19JCZDJC37300 and 17JCZDJC38100)supported by the Science and Technology Plans of Tianjin(Nos.17PTSYJC00040 and 18PTSYJC00180)。
文摘Bimetallic metal organic framework(MOF)as a precursor to prepare catalysts with bifunctional catalytic activity of oxygen evolution reaction(OER)and hydrogen evolution reaction(HER)attracts more and more attention.Herein,hollow oxygen deficiency-enriched NiFe_(2)O_(4) is synthesized by pyrolytic FeNi bimetallic MOF.The defects of rGO during carbonization can act as nucleation sites for FeNi particles.After nucleation and N doping,the FeNi particles were served as catalysts for the deposition of dissolved carbon in the defects of the N/rGO.These deposited carbon,like a bridge,connect N/rGO and hollow oxygen deficiency-enriched NiFe_(2)O_(4) together,which giving full play to the advantages of N/rGO in fast electron transfer,thereby improving its catalytic activity.The resultant NiFe_(2)O_(4)@N/rGO-800 exhibits a low overpotential of 252 mV at 20 mA cm^(-2) for OER and 157 mV at 10 mA cm^(-2) for HER in 1 M KOH,respectively.When used as bifunctional electrodes for overall water splitting,it also shows low cell voltage of 1.60 V and 1.67 V at 10 and 20 mA cm^(-2),respectively.
基金This work was financially supported by the National Natural Science Foundation of China(Nos.22008180 and 21878231)the Natural Science Foundation of Tianjin(Nos.19JCQNJC05700 and 19JCZDJC37300)the Tianjin College Student Innovation and Entrepreneurship Training Program(No.202010058034).This work was also supported by the Analytical&Testing Center of Tiangong University for structural characterization tests.
文摘Due to unique electrical properties and high catalytic efficiency,transition metal nitrogen-codoped car-bide(TM-N-C)has attracted tremendous interest as a multifunctional electrocatalyst for water splitting.Unlike traditional single-source modification,herein a novel pomegranate-like high-entropy(HE)elec-trocatalyst of Ni_(3)ZnC_(0.7)decorated with homogeneous multimetal(Fe,Co,Cu,and Ni)nitrogen-codoped carbon matrix(Ni_(3)ZnC_(0.7)@CoNiCuFe-NC)is reported.It can be implemented by the simple thermal an-nealing method of multimetal codoped zeolitic imidazolate framework(ZIF).Benefiting from the syn-ergistic effects of plentiful TM-N-C species,template effect of ZIF and distinct nanoporous structure,HE electrocatalyst Ni_(3)ZnC_(0.7)@CoNiCuFe-NC exhibits outstanding electrocatalytic performance.When ap-plied in strong alkaline electrolyte(1.0 M KOH),the overpotentials of Ni_(3)ZnC_(0.7)@CoNiCuFe-NC present as low as 202 and 97 mV for oxygen evolution reaction(OER)and hydrogen evolution reaction(HER)at 10 mA cm^(−2)current density.Surprisingly as a bifunctional electrode,it can achieve the low cell voltage of 1.53 V at 10 mA cm^(−2)current density for overall water splitting,which is comparable to conventional IrO_(2)||Pt/C electrode and superior to the recently reported analogous bifunctional catalysts.Thus,the work proposes the direction for the rational design of homogeneous distribution of TM-N-C material for water splitting in the green hydrogen energy industry.
基金the financial support from the National Natural Science Foundation of China(Nos.21878231 and 51603145)the Tianjin Natural Science Foundation of China(Nos.17JC ZDJ38100 and 19JCZDJC37300)+2 种基金the Science and Technology Plans of Tianjin(Nos.17PT SYJC00040 and 18PTSY JC00180)the China National Textile and Apparel Council(J201406)the China Petroleum Chemical Co Technology Development Project(216090 and 218008-6)。
文摘The aqueous rechargeable Zn-ion batteries based on the safe,low cost and environmental benignity aqueous electrolytes are one of the most compelling candidates for large scale energy storage applications.However,pursuing suitable insertion materials may be a great challenge due to the strong electrostatic interaction between Zn^(^(2+))and cathode materials.Hence,a novel NaV_(6)O_(15)/V_(2)O_(5) skin-core heterostructure nanowire is reported via a one-step hydrothermal method and subsequent calcination for high-stable aqueous Zn-ion batteries(ZIBs).The NaV_(6)O_(15)/V_(2)O_(5) cathode delivers high specific capacity of 390 m Ah/g at 0.3 A/g and outstanding cycling stability of 267 m Ah/g at 5 A/g with high capacity retention over 92.3%after 3000 cycles.The superior electrochemical performances are attributed to the synergistic effect of skin-core heterostructured NaV_(6)O_(15)/V_(2)O_(5),in which the sheath of NaV_(6)O_(15) possesses high stability and conductivity,and the V_(2)O_(5) endows high specific capacity.Besides,the heterojunction structure not only accelerates intercalation kinetics of Zn^(2+)transport but also further consolidates the stability of the layers of V_(2)O_(5) during the cyclic process.This work provides a new perspective in developing feasible insertion materials for rechargeable aqueous ZIBs.
基金supported by the National Natural Science Foundation of China(Grant Nos.11972165,and 11502085)the Japan Society for the Promotion of Science(Grant No.P18067)the Fundamental Research Funds for the Central Universities of China(Grant No.2016YXMS097)。
文摘Single crystals subjected to shock compression exhibit responses with distinct two-wave structures for certain crystal orientations.However,little is known to date regarding how the shock response depends on crystal orientation,and especially why the two-wave structure depends on the crystal orientation.In this work,molecular dynamics simulations of shock compressions in copper single crystals are performed to investigate the orientation dependence of shock responses and the corresponding deformation mechanisms.Four copper single crystals with[001],[011],[012],and[123]crystal orientations along the depth direction are investigated.The[011],[012],and[123]crystal orientations of copper single crystals show distinct two-wave structures in their shock responses,while such a two-wave structure in the shock response is not seen for those orientations having a[001]crystal orientation.The potential causes are analyzed by considering the propagation velocities of both elastic and plastic waves.We develop a technique for identifying twin structures in face-centered cubic crystals and this technique can effectively identify the twin structure.The morphology of shock-induced defects(e.g.,dislocations and twins)shows the significant dependence of crystal orientation and the mechanisms behind these are discussed in detail.Finally,the Johnson-Cook constitutive model describing dynamic deformations at high temperatures and high strain rates is used to analyze the relationships between the shock responses and microscopic defects.The predictions of the Johnson-Cook constitutive model are consistent with the results of the molecular dynamics simulations.
基金supported by the National Natural Science Foundation of China(No.51536001 and No.51776053)。
文摘In this paper,numerical investigation of hypersonic gas flow over two typical gap-cavity structures is carried out using all-speed preconditioned density-based solver.Such structures filled with porous seal in the gap are often present at the joint locations of control surfaces of the hypersonic vehicles.Single-domain approach is adopted to integrate the governing equations for both porous and fluid regions.The basic thermal invasion characteristic is first illustrated using the maze gap-cavity structure without sealing.Then,the influence of seal filling depth on the thermal invasion characteristic is investigated for the structure with sealing.Finally,a comparison of thermal invasion characteristics between maze and straight gap-cavity structures is performed to examine the influence of gap bending.Results show that the main source of hot airflow invading into the gap is from the millimeter scale gas layer within the boundary layer.And the invasion characteristic presents approximate stationary behavior.A primary vortex occurs in the gap adjacent to the leeward wall,which is ascribed to the impinging effect between the separate boundary flow and the windward wall.This effect is also the main driving force of thermal invasion.A treatment of filling the seal in certain depth inside the gap can significantly reduce the thermal load of seal and maintain an acceptable level of the invading mass flow rate.Additionally,it is found that the gap bending exerts a limited block effect on the thermal invasion without sealing,and this effect can be ignored with sealing.These results can provide a reference for optimizing the seal gap-cavity structure configuration.
基金supported by the financial support from NSFC (Grant 11472113 and Grant 11272130)
文摘The interactions between the moving dislocation within matrix channel and the interfacial misfit dislocation networks on the two-phase interfaces in Ni-based single crystal superalloys are studied carefully via atomic modeling, with special focus on the factors influ- encing the critical bowing stress of moving dislocations in the matrix channel. The results show that the moving matrix dislocation type and its position with respect to the interfacial misfit dislocation segments have considerable influences on the interactions. If the moving matrix dislocation is pure screw, it reacts with the interracial misfit dislocation segments toward dislocation linear energy reduction, which decreases the critical bowing stress of screw dislocation due to dislocation linear energy release during the dislocation reactions. If the moving matrix dislocation is of 60^-mixed type, it is obstructed by the interaction between the mixed matrix dislocations and the misfit interfacial dislocation segments. As a result, the critical bowing stress increases significantly because extra interactive energy needs to be overcome. These two different effects on the critical bowing stress become in- creasingly significant when the moving matrix dislocation is very close to the interracial misfit dislocation segments. In addition, the matrix channel width also has a significant influence on the critical bowing stress, i.e. the narrower the matrix channel is, the higher the critical bowing stress is. The classical Orowan formula is modified to predict these effects on the critical bowing stress of moving matrix dislocation, which is in good agreement with the computational results.
文摘The hydrogen effect on the nucleation and motion of dislocations in single-crystal bcc Fe with(110)surface was investigated by both nanoindentation experiments and discrete dislocation dynamics(DDD)simulation.The results of nanoindentation experiments showed that the pop-in load decreased evidently for the electrochemical hydrogen charging specimen,indicating that the dislocation nucleation strength might be reduced by hydrogen.In addition,the decrease of hardness due to hydrogen charging was also captured,implying that the dislocation motion might be promoted by hydrogen.By incorporating the effect of hydrogen on dislocation core energy,a DDD model was specifically proposed to investigate the influence of hydrogen on dislocation nucleation and motion.The results of DDD simulation revealed that under the effect of hydrogen,the dislocation nucleation strength is decreased and the motion of dislocation is promoted.