Rational design of Fe and N co-doped carbon catalysts(FeNCs), one promising non-precious cathode catalyst, is critical to commercialization of proton exchange membrane fuel cells. The atomic Fe site density of Fe-NCs ...Rational design of Fe and N co-doped carbon catalysts(FeNCs), one promising non-precious cathode catalyst, is critical to commercialization of proton exchange membrane fuel cells. The atomic Fe site density of Fe-NCs is critical to improve catalytic currents approaching industrial levels. One recent research proposes a template-guided strategy to break the limit of Fe site density, and greatly promotes the fuel cell performance.展开更多
Designing flexible free-standing air-electrode with efficient OER/ORR performance is of vital importance for the application of Zinc-air batteries in flexible electronics.Herein,a flexible free-standing electrode(Ni/F...Designing flexible free-standing air-electrode with efficient OER/ORR performance is of vital importance for the application of Zinc-air batteries in flexible electronics.Herein,a flexible free-standing electrode(Ni/Fe-NC/NCF/CC)is synthesized by in-situ coupling of binary Ni/Fe-NC nanocubes and N-doped carbon nanofibers(NCF)rooted on carbon cloth.The highly dispersed binary Ni/Fe-NC sites ensure excellent ORR activity and create efficient OER active sites relative to Ni-NC and Fe-NC.The in-situ coupling of Ni/Fe-NC and NCF constructs a 3D interconnected network structure that not only provides abundant and stabilized reactive sites but also guarantees fast electron transfer and gas transportation,thus achieving efficient and fast operation of ORR/OER.Therefore,Ni/Fe-NC/NCF/CC displays a much positive potential(0.952 V)at 4.0 mA cm^(-2)for ORR and a low OER overpotential(310 mV)at 50 mA cm^(-2).The Zinc-air battery with Ni/Fe-NC/NCF/CC air-electrode exhibits excellent battery performance with outstanding discharge/charge durability for 2150 cycles.The flexible Zn-air batteries with foldable mechanical properties display a high power density of 105.0 mW cm^(-2).This work widened the way to prepare flexible bifunctional air-electrode by designing composition/structure and in-situ coupling.展开更多
首先以二甲基咪唑锌盐ZIF-8为模板,在ZIF-8颗粒中进行原位铁离子的掺杂。在制备过程中加入氧化石墨烯(GO)进行复合,将得到的固体经高温碳化后制备出Fe@NC/还原氧化石墨烯复合纳米材料。采用扫描电子显微镜(SEM)、投射电子显微镜(TEM)以...首先以二甲基咪唑锌盐ZIF-8为模板,在ZIF-8颗粒中进行原位铁离子的掺杂。在制备过程中加入氧化石墨烯(GO)进行复合,将得到的固体经高温碳化后制备出Fe@NC/还原氧化石墨烯复合纳米材料。采用扫描电子显微镜(SEM)、投射电子显微镜(TEM)以及X射线衍射(XRD)表征材料的形貌和结构。将Fe@NC/r GO复合纳米材料制成墨液,分散在工作电极有效区后晾干用于测量材料的甲醇氧化活性,结果显示:用Fe@NC/r GO复合纳米材料制备而成的活性电极在0.5 M KOH+1 M CH3OH和进行循环伏安测试,在30 m Vs^(-1)扫速下,电压为0.88 V时,电流密度高达112.3 m A cm^(-2)。在对材料的循环稳定性进行测试时,在30 m V s^(-1)扫速下进行高达500圈的循环之后,峰电流密度也能保持原电流密度的73.45%,表明Fe@NC/rGO复合纳米材料具有优异的稳定性。展开更多
The numerical control (NC) precision bending process of thin-walled tube is on e of advanced plastic forming processes with high efficiency, forming precision, strength/weight ratio and low cost, thus it is playing mo...The numerical control (NC) precision bending process of thin-walled tube is on e of advanced plastic forming processes with high efficiency, forming precision, strength/weight ratio and low cost, thus it is playing more and more important role in manufacturing parts in aerospace and automobile industries. However, the determination of parameters crucial to make sure tube parts qualified is heavil y experience-based and involves repeated trial-and-errors in practice, which makes the production efficiency reduce drastically and does not fulfill the deve lopment of high technology. With quick development of computer technology and gr adual perfect of plastic forming theory, computer numerical simulation based on finite element method (FEM) has become one of important tools of researching and developing plastic forming technology. Development trend of NC precision bendin g process of tube is simulating its forming process by FEM. Because NC tube bend ing is of 3D nature, it is of great importance to analyze the forming mechanism and find out the influence law of forming parameters on forming process in the N C precision bending process of thin-walled tube quantitatively by 3D FE simulat ion. Based on the rigid-plastic finite element method (FEM) principle, a 3-dimens ional (3D) rigid-plastic FE simulation system named TBS -3D (tube bending simu lation by 3D FEM) for the NC bending process of thin-walled tube has been devel oped, a reasonable FEM model has been established. By use of this FEM simulation system, a NC bending process of thin-walled has been simulated. And deformed m eshes under different bending stages, stress distribution along bending directio n, relationship between maximal wall thickness changing ratio and bending angle have been obtained. And then some forming laws of NC tube bending obtained are a s follows: (1) NC bending process make tube elongate to some extent; (2) Charact eristic of stress distribution is that the outer area is undergoing tensile stre ss, the inner area is undergoing compression stress, and stress neutral layer mo ves close to the inner area, which is in good accordance with the practice; (3) Maximal wall thinning ratio in the outer tensile area changes only a little with increase of bending angle, and maximal wall thickening ratio in the inner compr ession area increases linearly with bending angle. The above results show that 3 D FE simulation is an important and valid tool of analyzing NC bending process o f tube, this research is beneficial for the practical tube bending process, and it may serve as a significant guide to the practice of the relevant processes.展开更多
Thermal stability and strain rate sensitivity of ultrafine-grained(UFG)Fe produced by severe plastic deformation(SPD)were investigated.The UFG Fe was processed by equal-channel angular pressing(ECAP)via route Bc.After...Thermal stability and strain rate sensitivity of ultrafine-grained(UFG)Fe produced by severe plastic deformation(SPD)were investigated.The UFG Fe was processed by equal-channel angular pressing(ECAP)via route Bc.After 6 passes,the grain size of UFG Fe reaches 600 nm, as confirmed by means of electron back scatter diffraction(EBSD).Examination of micro-hardness and grain size of UFG Fe as a function of post-ECAP annealing temperature shows a transition from recovery to recrystallization.The critical transition temperature is approximately 500℃,and the material has a bimodal structure after annealing at this temperature.Deformation behaviors of ECAP Fe and ECAP + annealing Fe were studied under both quasi-static and dynamic compressive loadings.The UFG iron shows increased strength and reduced strain rate sensitivity compared with its coarse-grained counterparts.The appropriate post-ECAP annealing can increase strain hardening ability and cancel out thermal softening effect with only a small loss of strength under dynamic loading.展开更多
Concave nanostructures may be developed to improve the specific mass activity of a catalyst for formic acid and methanol electro-oxidation. In this work, we report the elctrocatalytic oxidation of methanol and formic ...Concave nanostructures may be developed to improve the specific mass activity of a catalyst for formic acid and methanol electro-oxidation. In this work, we report the elctrocatalytic oxidation of methanol and formic acid in acid medium over concave Pt-Cu-Fe ternary nanocubes（NCs）, obtained by the galvanic exchange of Pt and Fe on Cu NCs. The concave Pt-Cu-Fe NCs exhibited improved electrooxidation performance contrasted to Pt-Cu NCs and purchased commercial Pt/C as demonstrated by their improved durability, lower onset potential, and more preferable anti-poisoning properties. These properties are believed to originate from the tailored concave structure of the catalyst and possible synergetic effects among the components of the Pt-Cu-Fe NCs.展开更多
文摘Rational design of Fe and N co-doped carbon catalysts(FeNCs), one promising non-precious cathode catalyst, is critical to commercialization of proton exchange membrane fuel cells. The atomic Fe site density of Fe-NCs is critical to improve catalytic currents approaching industrial levels. One recent research proposes a template-guided strategy to break the limit of Fe site density, and greatly promotes the fuel cell performance.
基金supported by the National Natural Science Foundation of China(Grants:51861135315,U1766216,51774148,51804128,52177215,51977097)
文摘Designing flexible free-standing air-electrode with efficient OER/ORR performance is of vital importance for the application of Zinc-air batteries in flexible electronics.Herein,a flexible free-standing electrode(Ni/Fe-NC/NCF/CC)is synthesized by in-situ coupling of binary Ni/Fe-NC nanocubes and N-doped carbon nanofibers(NCF)rooted on carbon cloth.The highly dispersed binary Ni/Fe-NC sites ensure excellent ORR activity and create efficient OER active sites relative to Ni-NC and Fe-NC.The in-situ coupling of Ni/Fe-NC and NCF constructs a 3D interconnected network structure that not only provides abundant and stabilized reactive sites but also guarantees fast electron transfer and gas transportation,thus achieving efficient and fast operation of ORR/OER.Therefore,Ni/Fe-NC/NCF/CC displays a much positive potential(0.952 V)at 4.0 mA cm^(-2)for ORR and a low OER overpotential(310 mV)at 50 mA cm^(-2).The Zinc-air battery with Ni/Fe-NC/NCF/CC air-electrode exhibits excellent battery performance with outstanding discharge/charge durability for 2150 cycles.The flexible Zn-air batteries with foldable mechanical properties display a high power density of 105.0 mW cm^(-2).This work widened the way to prepare flexible bifunctional air-electrode by designing composition/structure and in-situ coupling.
文摘首先以二甲基咪唑锌盐ZIF-8为模板,在ZIF-8颗粒中进行原位铁离子的掺杂。在制备过程中加入氧化石墨烯(GO)进行复合,将得到的固体经高温碳化后制备出Fe@NC/还原氧化石墨烯复合纳米材料。采用扫描电子显微镜(SEM)、投射电子显微镜(TEM)以及X射线衍射(XRD)表征材料的形貌和结构。将Fe@NC/r GO复合纳米材料制成墨液,分散在工作电极有效区后晾干用于测量材料的甲醇氧化活性,结果显示:用Fe@NC/r GO复合纳米材料制备而成的活性电极在0.5 M KOH+1 M CH3OH和进行循环伏安测试,在30 m Vs^(-1)扫速下,电压为0.88 V时,电流密度高达112.3 m A cm^(-2)。在对材料的循环稳定性进行测试时,在30 m V s^(-1)扫速下进行高达500圈的循环之后,峰电流密度也能保持原电流密度的73.45%,表明Fe@NC/rGO复合纳米材料具有优异的稳定性。
文摘The numerical control (NC) precision bending process of thin-walled tube is on e of advanced plastic forming processes with high efficiency, forming precision, strength/weight ratio and low cost, thus it is playing more and more important role in manufacturing parts in aerospace and automobile industries. However, the determination of parameters crucial to make sure tube parts qualified is heavil y experience-based and involves repeated trial-and-errors in practice, which makes the production efficiency reduce drastically and does not fulfill the deve lopment of high technology. With quick development of computer technology and gr adual perfect of plastic forming theory, computer numerical simulation based on finite element method (FEM) has become one of important tools of researching and developing plastic forming technology. Development trend of NC precision bendin g process of tube is simulating its forming process by FEM. Because NC tube bend ing is of 3D nature, it is of great importance to analyze the forming mechanism and find out the influence law of forming parameters on forming process in the N C precision bending process of thin-walled tube quantitatively by 3D FE simulat ion. Based on the rigid-plastic finite element method (FEM) principle, a 3-dimens ional (3D) rigid-plastic FE simulation system named TBS -3D (tube bending simu lation by 3D FEM) for the NC bending process of thin-walled tube has been devel oped, a reasonable FEM model has been established. By use of this FEM simulation system, a NC bending process of thin-walled has been simulated. And deformed m eshes under different bending stages, stress distribution along bending directio n, relationship between maximal wall thickness changing ratio and bending angle have been obtained. And then some forming laws of NC tube bending obtained are a s follows: (1) NC bending process make tube elongate to some extent; (2) Charact eristic of stress distribution is that the outer area is undergoing tensile stre ss, the inner area is undergoing compression stress, and stress neutral layer mo ves close to the inner area, which is in good accordance with the practice; (3) Maximal wall thinning ratio in the outer tensile area changes only a little with increase of bending angle, and maximal wall thickening ratio in the inner compr ession area increases linearly with bending angle. The above results show that 3 D FE simulation is an important and valid tool of analyzing NC bending process o f tube, this research is beneficial for the practical tube bending process, and it may serve as a significant guide to the practice of the relevant processes.
基金supported by the National Natural Science Foundation of China(11002151,110722432)973 Project(2010CB631004)
文摘Thermal stability and strain rate sensitivity of ultrafine-grained(UFG)Fe produced by severe plastic deformation(SPD)were investigated.The UFG Fe was processed by equal-channel angular pressing(ECAP)via route Bc.After 6 passes,the grain size of UFG Fe reaches 600 nm, as confirmed by means of electron back scatter diffraction(EBSD).Examination of micro-hardness and grain size of UFG Fe as a function of post-ECAP annealing temperature shows a transition from recovery to recrystallization.The critical transition temperature is approximately 500℃,and the material has a bimodal structure after annealing at this temperature.Deformation behaviors of ECAP Fe and ECAP + annealing Fe were studied under both quasi-static and dynamic compressive loadings.The UFG iron shows increased strength and reduced strain rate sensitivity compared with its coarse-grained counterparts.The appropriate post-ECAP annealing can increase strain hardening ability and cancel out thermal softening effect with only a small loss of strength under dynamic loading.
文摘Concave nanostructures may be developed to improve the specific mass activity of a catalyst for formic acid and methanol electro-oxidation. In this work, we report the elctrocatalytic oxidation of methanol and formic acid in acid medium over concave Pt-Cu-Fe ternary nanocubes（NCs）, obtained by the galvanic exchange of Pt and Fe on Cu NCs. The concave Pt-Cu-Fe NCs exhibited improved electrooxidation performance contrasted to Pt-Cu NCs and purchased commercial Pt/C as demonstrated by their improved durability, lower onset potential, and more preferable anti-poisoning properties. These properties are believed to originate from the tailored concave structure of the catalyst and possible synergetic effects among the components of the Pt-Cu-Fe NCs.
