Production of green hydrogen through water electrolysis powered by renewable energy sources has garnered increasing attention as an attractive strategy for the storage of clean and sustainable energy.Among various ele...Production of green hydrogen through water electrolysis powered by renewable energy sources has garnered increasing attention as an attractive strategy for the storage of clean and sustainable energy.Among various electrolysis technologies,the emerging anion exchange membrane water electrolyser(AEMWE)exhibits the most potential for green hydrogen production,offering a potentially costeffective and sustainable approach that combines the advantages of high current density and fast start from proton exchange membrane water electrolyser(PEMWE)and low-cost catalyst from traditional alkaline water electrolyser(AWE)systems.Due to its relatively recent emergence over the past decade,a series of efforts are dedicated to improving the electrochemical reaction performance to accelerate the development and commercialization of AEMWE technology.A catalytic electrode comprising a gas diffusion layer(GDL)and a catalyst layer(CL)is usually called a gas diffusion electrode(GDE)that serves as a fundamental component within AEMWE,and also plays a core role in enhancing mass transfer during the electrolysis process.Inside the GDEs,bubbles nucleate and grow within the CL and then are transported through the GDL before eventually detaching to enter the electrolyte in the flow field.The transfer processes of water,gas bubbles,charges,and ions are intricately influenced by bubbles.This phenomenon is referred to as bubble-associated mass transfer.Like water management in fuel cells,effective bubble management is crucial in electrolysers,as its failure can result in various overpotential losses,such as activation losses,ohmic losses,and mass transfer losses,ultimately degrading the AEMWE performance.Despite significant advancements in the development of new materials and techniques in AEMWE,there is an urgent need for a comprehensive discussion focused on GDEs,with a particular emphasis on bubbleassociated mass transfer phenomena.This review aims to highlight recent findings regarding mass transfer in GDEs,particularly the impacts of bubble accumulation;and presents the latest advancements in designing CLs and GDLs to mitigate bubble-related issues.It is worth noting that a series of innovative bubble-free-GDE designs for water electrolysis are also emphasized in this review.This review is expected to be a valuable reference for gaining a deeper understanding of bubble-related mass transfer,especially the complex bubble behavior associated with GDEs,and for developing innovative practical strategies to advance AEMWE for green hydrogen production.展开更多
The effects of chloride and thiosulfate ions on localized corrosion of alloy 800 are investigated through dynamical observation of the change in phase image of the diffusion layer during passive film breakdown using d...The effects of chloride and thiosulfate ions on localized corrosion of alloy 800 are investigated through dynamical observation of the change in phase image of the diffusion layer during passive film breakdown using digital holography. The results indicate that solution chemistry has a significant effect on film breakdown and diffusion layer. The phase distribution changes at different applied potentials show that in the process of film breakdown, dissolution of metal ions from pitting is not remarkable in chloride-only solution, whereas dissolution of metal ions is significantly high in thiosulfate and chloride solution. Thiosulfate has a combined effect with chloride ions in passive film degradation.展开更多
Comparative studies of four common-used anode gas diffusion layers(A-GDLs),namely carbon cloth,carbon paper,carbon paper based on XC-72(in short XC-72)and GDL made of carbon nanotubes(CNT)for direct methanol fuel cell...Comparative studies of four common-used anode gas diffusion layers(A-GDLs),namely carbon cloth,carbon paper,carbon paper based on XC-72(in short XC-72)and GDL made of carbon nanotubes(CNT)for direct methanol fuel cells(DMFCs)were carried out and discussed.The results of scanning electron microscope(SEM),mercury intrusion porosimeter(MIP)and electrochemical test show that CNT has large pore size distribution in pore size of 1000-3000nm and the largest total porosity compared with those of the other three.Carbon paper and XC-72show disadvantageous influences on cell performances at high current density,because carbon paper has many large pores which are unsuited for water transport,while XC-72has many small pores which are unsuited for gas transport.Though cell with carbon cloth has the highest methanol diffusion coefficient,it shows a little lower performance than that with CNT due to its thickness.Anode polarization(AP)results also display that the cell with CNT has the least methanol mass transfer resistance.As a result,the cell with CNT shows the best performance with the highest limiting current density and peak power density of 460 mA·cm^(-2)and 110mW·cm^(-2),respectively.展开更多
The aim of this study is to show how fractal analysis can be effectively used to characterize the texture of porous solids. The materials under study were carbon papers, the backing material of the gas diffusion lay...The aim of this study is to show how fractal analysis can be effectively used to characterize the texture of porous solids. The materials under study were carbon papers, the backing material of the gas diffusion layer （GDL） in Proton Exchange Membrane Fuel Cell （PEMFC）. The fractal dimensions were calculated by analyzing data from mercury porosimetry. The polytotrafluoroethylene （PTFE） treated carbon paper shows a significantly high fractal dimension value than pare sample, and the high fractal dimension signifies that the physical complexity of the pore surface is enhanced. The fractal dimension can be used as a valid parameter to monitor the textural evolution of the samples as the treatment progresses, as this behaves in a similar way to other textural parameters. The use of fractal analysis in conjunction with the results of classical characterization methods leads to a better understanding of textural modificatious in the processing of materials.展开更多
The diffusion layers in substitution-permutation network（SPN） block ciphers are almost invertible linear transformations, which is optimal if the branch number reaches the maximum value. The method of constructing i...The diffusion layers in substitution-permutation network（SPN） block ciphers are almost invertible linear transformations, which is optimal if the branch number reaches the maximum value. The method of constructing involutory optimal diffusion layers is proposed based on the Cauchy matrix, which can decrease the cost of implementation. The analysis to experimental results indicates that the diffusion layer ensures the security of the SPN block cipher against differential cryptanalysis（DC） and linear cryptanalysis（LC）, and decreases half the cost of implementation.展开更多
Water management is a key to ensuring high performance and durability of polymer electrolyte fuel cell(PEFC),and it is important to understand the behavior of liquid water in PEFC.In this study,the two-phase lattice B...Water management is a key to ensuring high performance and durability of polymer electrolyte fuel cell(PEFC),and it is important to understand the behavior of liquid water in PEFC.In this study,the two-phase lattice Boltzmann method is applied to the simulations of water discharge from gas diffusion layers(GDL)to gas channels.The GDL is porous media composed of carbon fibers with hydrophobic treatment,and the gas channels are hydrophilic micro-scale ducts.In the simulations,arbitrarily generated porous materials are used as the structures of the GDL.We investigate the effects of solid surface wettabilities on water distribution in the gas channels and the GDL.Moreover,the results of X-ray computed tomography images in the operating PEFC are compared with the numerical simulations,and the mechanism of the water transport in PEFC is considered.展开更多
Gas diffusion layer(GDL) plays a great important role in proton exchange membrane fuel cell(PEMFC).Water transport mechanism in GDL is still not clear.In the present study,an ex-situ transparent setup is built to visu...Gas diffusion layer(GDL) plays a great important role in proton exchange membrane fuel cell(PEMFC).Water transport mechanism in GDL is still not clear.In the present study,an ex-situ transparent setup is built to visualize the transport phenomena and to measure the threshold pressure of water in GDL at different temperatures.It is found that the relationship between the breakthrough pressure and the temperature is nearly linear(i.e.the pressure decreases linearly with the increase of temperature).To avoid the problems faced by the continuum models,the pore network model is developed to simulate the liquid water transport through the carbon paper.A uniform pressure boundary condition is used in simulation and the results are similar to the ones obtained in the experiment.The reason is that the contact angle and surface tension coefficient of water in GDLs change accordingly with the change of temperature.展开更多
This paper studied the breakthrough pressure for liquid water to penetrate the gas diffusion layer(GDL) of a proton exchange membrane fuel cell(PEMFC).An ex-situ testing was conducted on a transparent test cell to vis...This paper studied the breakthrough pressure for liquid water to penetrate the gas diffusion layer(GDL) of a proton exchange membrane fuel cell(PEMFC).An ex-situ testing was conducted on a transparent test cell to visualize the water droplet formation and detachment on the surface of different types of GDLs through a CCD camera.The breakthrough pressure,at which the liquid water penetrates the GDL and starts to form a droplet,was measured.The breakthrough pressure was found to be different for the GDLs with different porosities and thicknesses.The equilibrium pressure,which is defined as the minimum pressure required maintaining a constant flow through the GDL,was also recorded.The equilibrium pressure was found to be much lower than the breakthrough pressure for the same type of GDL.A pore network model was modified to further study the relationship between the breakthrough pressure and the GDL properties and thicknesses.The breakthrough pressure increases for the thick GDL with smaller micro-pore size.展开更多
We report the electrochemical performance of Ni(OH)_(2) on a gas diffusion layer(GDL).The Ni(OH)_(2) working electrode was successfully prepared via a simple method,and its electrochemical performance in 1 M NaOH elec...We report the electrochemical performance of Ni(OH)_(2) on a gas diffusion layer(GDL).The Ni(OH)_(2) working electrode was successfully prepared via a simple method,and its electrochemical performance in 1 M NaOH electrolyte was investigated.The electrochemical results showed that the Ni(OH)_(2)/GDL provided the maximum specific capacitance value(418.11 F·g^(−1))at 1 A·g^(−1).Furthermore,the Ni(OH)_(2) electrode delivered a high specific energy of 17.25 Wh·kg^(−1) at a specific power of 272.5 W·kg^(−1) and retained about 81%of the capacitance after 1000 cycles of galvanostatic charge–discharge(GCD)measurements.The results of scanning electron microscopy(SEM)coupled with energy-dispersive X-ray spectroscopy(EDS)revealed the occurrence of sodium deposition after long-time cycling,which caused the reduction in the specific capacitance.This study results suggest that the light-weight GDL,which can help overcome the problem of the oxide layer on metal–foam substrates,is a promising current collector to be used with Ni-based electroactive materials for energy storage applications.展开更多
The lattice Boltzmann method is applied to the investigations of the diffusivity and the permeability in the gas diffusion layer(GDL)of the polymer electrolyte fuel cell(PEFC).The effects of the configuration of water...The lattice Boltzmann method is applied to the investigations of the diffusivity and the permeability in the gas diffusion layer(GDL)of the polymer electrolyte fuel cell(PEFC).The effects of the configuration of water droplets,the porosity of the GDL,the viscosity ratio of water to air,and the surface wettability of the GDL are investigated.From the simulations under the PEFC operating conditions,it is found that the heterogeneous water network and the high porosity improve the diffusivity and the permeability,and the hydrophobic surface decreases the permeability.展开更多
To study the effect of annealing temperature on the joints between magnesium and aluminum alloys, and improve the properties of bonding layers, composite plates of magnesium alloy（AZ31 B） and aluminum alloy（6061） ...To study the effect of annealing temperature on the joints between magnesium and aluminum alloys, and improve the properties of bonding layers, composite plates of magnesium alloy（AZ31 B） and aluminum alloy（6061） were welded using the vacuum diffusion bonding method. The composite specimens were continuously annealed in an electrical furnace under the protection of argon gas. The microstructures were then observed using scanning electron microscopy. X-ray diffractometry was used to investigate the residual stresses in the specimens. The elemental distribution was analyzed with an electron probe micro analyzer. The tensile strength and hardness were also measured. Results show that the diffusion layers become wide as the heat treatment temperature increases, and the residual stress of the specimen is at a minimum and tensile strength is the largest when being annealed at 250 ℃. Therefore, 250 ℃ is the most appropriate annealing temperature.展开更多
In many circumstances,dissimilar metals have to be bonded together and the resulting joint interfaces must typically sustain mechanical and/or electrical forces without failure,which is not possible by fusion welding ...In many circumstances,dissimilar metals have to be bonded together and the resulting joint interfaces must typically sustain mechanical and/or electrical forces without failure,which is not possible by fusion welding processes.The melting points of magnesium(Mg)and copper(Cu)have a significant difference(nearly 400℃)and this may lead to a large difference in the microstructure and joint performance of Mg-Cu joints.However,diffusion bonding can be used to join these alloys without much difficulty.This work analyses the effect of parameters on diffusion layer thickness,hardness and strength of magnesium-copper dissimilar joints.The experiments were conducted using three-factor,five-level,central composite rotatable design matrix.Empirical relationships were developed to predict diffusion layer thickness,hardness and strength using response surface methodology.It is found that bonding temperature has predominant effect on bond characteristics.Joints fabricated at a bonding temperature of 450℃, bonding pressure of 12 MPa and bonding time of 30 min exhibited maximum shear strength and bonding strength of 66 and 81 MPa, respectively.展开更多
Ti-6Al-4V(wt.%) and Ti-22Al-25Nb(at.%) were joined by diffusion bonding at 950 ℃ and 15 MPa for 100 min, and the microstructure and mechanical properties of the resulting joints were investigated. The composition of ...Ti-6Al-4V(wt.%) and Ti-22Al-25Nb(at.%) were joined by diffusion bonding at 950 ℃ and 15 MPa for 100 min, and the microstructure and mechanical properties of the resulting joints were investigated. The composition of the diffusion layer is B2/discontinuous α/α2 layer/necklace-shaped β+α’ layer, where the content of any element at a given point mainly depends on the distance of the point from the interface and the phase type at the point. The tensile strength of the joint is 894 MPa, which is almost the same as that of the Ti-22Al-25Nb base alloy. The fracture surfaces on both sides of the joint are composed of two main regions. One region displays a relatively flat surface and fractures along the bonding interface. The other is composed of a moderate number of irregularly-shaped cavities on the Ti-6Al-4V side and many irregularly-shaped bulges on the Ti-22Al-25Nb side. Both regions result from fracture along the boundaries between β+α’ layers and αp grains or from the transcrystalline fracture of αp grains.展开更多
This study shows the preparation of a TiO2 coated Pt/C（TiO2/Pt/C） by atomic layer deposition（ALD）,and the examination of the possibility for TiO2/Pt/C to be used as a durable cathode catalyst in polymer electrolyt...This study shows the preparation of a TiO2 coated Pt/C（TiO2/Pt/C） by atomic layer deposition（ALD）,and the examination of the possibility for TiO2/Pt/C to be used as a durable cathode catalyst in polymer electrolyte fuel cells（PEFCs）. Cyclic voltammetry results revealed that TiO2/Pt/C catalyst which has 2 nm protective layer showed similar activity for the oxygen reduction reaction compared to Pt/C catalysts and they also had good durability. TiO2/Pt/C prepared by 10 ALD cycles degraded 70% after 2000 Accelerated degradation test, while Pt/C corroded 92% in the same conditions. TiO2 ultrathin layer by ALD is able to achieve a good balance between the durability and activity, leading to TiO2/Pt/C as a promising cathode catalyst for PEFCs. The mechanism of the TiO2 protective layer used to prevent the degradation of Pt/C is discussed.展开更多
A diffusive titanium nitride layers were produced on AZ91 D magnesium alloy by a hybrid method which combines the titanium coating physical vapor deposition（PVD） with subsequent nitriding. The layers are composed of...A diffusive titanium nitride layers were produced on AZ91 D magnesium alloy by a hybrid method which combines the titanium coating physical vapor deposition（PVD） with subsequent nitriding. The layers are composed of a thin surface zone of titanium nitrides and oxides, an intermediate titanium zone and Ti-Al-Mg type diffusive zone. Since the layers improve the corrosion resistance, the best corrosion resistance is obtained when the layers are produced on aluminum base sub-layer by oxynitriding.展开更多
The diffusive boundary layer （DBL） is the zone for matter exchange between surface water and aquatic sediments. To elucidate the influence of DBL on salt release from saline sediments to freshwater, two experiments ...The diffusive boundary layer （DBL） is the zone for matter exchange between surface water and aquatic sediments. To elucidate the influence of DBL on salt release from saline sediments to freshwater, two experiments with or without wind blowing were conducted. According to the experiments, a 3.5 cm DBL is formed above the smoothed sediments at a steady wind field and this thickness is greater than other studies. The observed flux of salt through the DBL is 6% larger than the calculated value from Fick＇ s first law. The results indicate that molecular diffusion is the dominant mechanism for salt transport through the DBL. The presence of DBL suppresses the hydrodynamic enhancement for matter exchange between sediments and overlying water. Therefore, salts in the sediments of a polder reservoir may influence the water quality chronically.展开更多
Homogenization annealing of the 7050/6009 bimetal slab prepared by direct-chill casting was investigated and its effects on microstructural evolution, composition distribution and mechanical properties in the interfac...Homogenization annealing of the 7050/6009 bimetal slab prepared by direct-chill casting was investigated and its effects on microstructural evolution, composition distribution and mechanical properties in the interfacial region of the bimetal were studied. The results show that the optimized homogenization annealing process was 460℃for 24 h. After homogenization annealing, the Zn-rich phases and Al15（FeMn）3Si2phases were precipitated at the interface of the bimetal. The diffusion layer thickness of homogenized bimetal increased by 30 μm from 440 to480℃for 24 h, while it increased by 280 μm from 12 to 36 h at 460℃. The Vickers hardnessesat 6009 alloy side and interface of the bimetal decreased after homogenized annealing and grain coarsening was considered asthedominating softening mechanism.The hardness variation at 7050 alloy side was complicated due to the combined action of solution strengthening, dispersion strengthening and dissolution of reinforced phases.展开更多
Cu/Al multilayers were produced by high-temperature accumulative roll bonding(ARB)methods up to three passes.To achieve a high bonding strength,prior to ARB processing,the Cu and Al sheets were heated to 350,400,450 a...Cu/Al multilayers were produced by high-temperature accumulative roll bonding(ARB)methods up to three passes.To achieve a high bonding strength,prior to ARB processing,the Cu and Al sheets were heated to 350,400,450 and 500 ℃,respectively.The mechanical properties were evaluated by tensile tests.The microstructure was examined by optical microscopy and scanning electron microscopy equipped with energy dispersive spectrometry.The ultimate tensile stress,the grain size and the thickness of diffusion layer of lamellar composites increase with rolling temperature.When the rolling temperature is 400 ℃,the laminates show the highest ductility,but the yield stress is the lowest.As the rolling temperature further increases,both the yield stress and the ultimate tensile stress increase and the ductility decreases slightly.The mechanical properties of lamellar composites processed by low and high temperature ARB are determined by grain size and the thickness of diffusion layer,respectively.展开更多
Corrugated cold roll bonding(CCRB) produces metal composite plate with improved mechanical properties compared with conventional methods,but the interfacial mechanism is not fully understood.Here,Cu/Al composite plate...Corrugated cold roll bonding(CCRB) produces metal composite plate with improved mechanical properties compared with conventional methods,but the interfacial mechanism is not fully understood.Here,Cu/Al composite plate with good plate shape was produced by CCRB,and the bonding mechanism and strength along the corrugated interface were studied by experiments and finite element simulations.The results showed that the average bonding strength of Cu/Al composite plate produced by CCRB was nearly twice that of conventional composite plate at an average reduction of 40% during rolling.Strong friction shear stresses occurred at the interface of the corrugated composite plate,which promoted the plastic deformation of the metals and accelerated the rupture of the brittle interfacial layer.Electron backscattered diffraction analysis showed that higher degrees of grain elongation and refinement occurred in the matrices at the front waist and trough due to the stronger normal and shear stresses.Energy-dispersive spectroscopy line scans showed that the thickest atomic diffusion layer occurred at the front waist.The present combination of experimental and computational analyses provides insights into the underlying mechanism of mechanically improved metal composites prepared by CCRB.展开更多
The effects of postweld heat treatment on the microstructure and metallurgical properties of a bronze–carbon steel(st37)explosively bonded interface were studied.Explosive welding was done under 1.5-and 2-mm standoff...The effects of postweld heat treatment on the microstructure and metallurgical properties of a bronze–carbon steel(st37)explosively bonded interface were studied.Explosive welding was done under 1.5-and 2-mm standoff distances and different conditions of explosive charge.Samples were postweld heat treated for 4 and 16 h in the furnace at 250°C and 500°C and then air cooled.Laboratory studies using optical microscopy,scanning electron microscopy,and microhardness testing were used to evaluate the welded samples.Microstructural examinations showed that by increasing the standoff distance and the explosive charge,the interface of bronze to steel became wavier.The microhardness test result showed that the hardness of the samples was higher near the joint interface compared with other areas because of the intensive plastic deformation,which was caused by the explosion force.The results show that increasing the heat treatment temperature and time caused the intermetallic compounds’layer thickness to increase,and,because of the higher diffusion of copper and tin,the iron amount in the intermetallic compounds decreased.Also,because of the increase in heat treatment temperature and time,internal stresses were released,and the interface hardness decreased.展开更多
基金support from the National Natural Science Foundation of China(Grant No.52006029)the Promotion Foundation for Young Science and Technology Talents in Jilin Province(Grant No.QT202113)+2 种基金the Special Foundation of Industrial Innovation in Jilin Province(Grant No.2019C056-2)the Special Foundation for Outstanding Young Talents Training in Jilin(Grant No.20200104107)the UK EPSRC(EP/W03784X/1)。
文摘Production of green hydrogen through water electrolysis powered by renewable energy sources has garnered increasing attention as an attractive strategy for the storage of clean and sustainable energy.Among various electrolysis technologies,the emerging anion exchange membrane water electrolyser(AEMWE)exhibits the most potential for green hydrogen production,offering a potentially costeffective and sustainable approach that combines the advantages of high current density and fast start from proton exchange membrane water electrolyser(PEMWE)and low-cost catalyst from traditional alkaline water electrolyser(AWE)systems.Due to its relatively recent emergence over the past decade,a series of efforts are dedicated to improving the electrochemical reaction performance to accelerate the development and commercialization of AEMWE technology.A catalytic electrode comprising a gas diffusion layer(GDL)and a catalyst layer(CL)is usually called a gas diffusion electrode(GDE)that serves as a fundamental component within AEMWE,and also plays a core role in enhancing mass transfer during the electrolysis process.Inside the GDEs,bubbles nucleate and grow within the CL and then are transported through the GDL before eventually detaching to enter the electrolyte in the flow field.The transfer processes of water,gas bubbles,charges,and ions are intricately influenced by bubbles.This phenomenon is referred to as bubble-associated mass transfer.Like water management in fuel cells,effective bubble management is crucial in electrolysers,as its failure can result in various overpotential losses,such as activation losses,ohmic losses,and mass transfer losses,ultimately degrading the AEMWE performance.Despite significant advancements in the development of new materials and techniques in AEMWE,there is an urgent need for a comprehensive discussion focused on GDEs,with a particular emphasis on bubbleassociated mass transfer phenomena.This review aims to highlight recent findings regarding mass transfer in GDEs,particularly the impacts of bubble accumulation;and presents the latest advancements in designing CLs and GDLs to mitigate bubble-related issues.It is worth noting that a series of innovative bubble-free-GDE designs for water electrolysis are also emphasized in this review.This review is expected to be a valuable reference for gaining a deeper understanding of bubble-related mass transfer,especially the complex bubble behavior associated with GDEs,and for developing innovative practical strategies to advance AEMWE for green hydrogen production.
基金supported by Natural Sciences and Engineering Research Council of Canada Discovery GrantNational Natural Science Foundation of China (No. 51371124)
文摘The effects of chloride and thiosulfate ions on localized corrosion of alloy 800 are investigated through dynamical observation of the change in phase image of the diffusion layer during passive film breakdown using digital holography. The results indicate that solution chemistry has a significant effect on film breakdown and diffusion layer. The phase distribution changes at different applied potentials show that in the process of film breakdown, dissolution of metal ions from pitting is not remarkable in chloride-only solution, whereas dissolution of metal ions is significantly high in thiosulfate and chloride solution. Thiosulfate has a combined effect with chloride ions in passive film degradation.
文摘Comparative studies of four common-used anode gas diffusion layers(A-GDLs),namely carbon cloth,carbon paper,carbon paper based on XC-72(in short XC-72)and GDL made of carbon nanotubes(CNT)for direct methanol fuel cells(DMFCs)were carried out and discussed.The results of scanning electron microscope(SEM),mercury intrusion porosimeter(MIP)and electrochemical test show that CNT has large pore size distribution in pore size of 1000-3000nm and the largest total porosity compared with those of the other three.Carbon paper and XC-72show disadvantageous influences on cell performances at high current density,because carbon paper has many large pores which are unsuited for water transport,while XC-72has many small pores which are unsuited for gas transport.Though cell with carbon cloth has the highest methanol diffusion coefficient,it shows a little lower performance than that with CNT due to its thickness.Anode polarization(AP)results also display that the cell with CNT has the least methanol mass transfer resistance.As a result,the cell with CNT shows the best performance with the highest limiting current density and peak power density of 460 mA·cm^(-2)and 110mW·cm^(-2),respectively.
基金Funded by the Natural Science Foundation of Hubei ( No.2003ABA088) and the Special Scientific Research Foundation forCollege Doctor Subjects from Ministry of Education of China (No.20030497012)
文摘The aim of this study is to show how fractal analysis can be effectively used to characterize the texture of porous solids. The materials under study were carbon papers, the backing material of the gas diffusion layer （GDL） in Proton Exchange Membrane Fuel Cell （PEMFC）. The fractal dimensions were calculated by analyzing data from mercury porosimetry. The polytotrafluoroethylene （PTFE） treated carbon paper shows a significantly high fractal dimension value than pare sample, and the high fractal dimension signifies that the physical complexity of the pore surface is enhanced. The fractal dimension can be used as a valid parameter to monitor the textural evolution of the samples as the treatment progresses, as this behaves in a similar way to other textural parameters. The use of fractal analysis in conjunction with the results of classical characterization methods leads to a better understanding of textural modificatious in the processing of materials.
文摘The diffusion layers in substitution-permutation network（SPN） block ciphers are almost invertible linear transformations, which is optimal if the branch number reaches the maximum value. The method of constructing involutory optimal diffusion layers is proposed based on the Cauchy matrix, which can decrease the cost of implementation. The analysis to experimental results indicates that the diffusion layer ensures the security of the SPN block cipher against differential cryptanalysis（DC） and linear cryptanalysis（LC）, and decreases half the cost of implementation.
文摘Water management is a key to ensuring high performance and durability of polymer electrolyte fuel cell(PEFC),and it is important to understand the behavior of liquid water in PEFC.In this study,the two-phase lattice Boltzmann method is applied to the simulations of water discharge from gas diffusion layers(GDL)to gas channels.The GDL is porous media composed of carbon fibers with hydrophobic treatment,and the gas channels are hydrophilic micro-scale ducts.In the simulations,arbitrarily generated porous materials are used as the structures of the GDL.We investigate the effects of solid surface wettabilities on water distribution in the gas channels and the GDL.Moreover,the results of X-ray computed tomography images in the operating PEFC are compared with the numerical simulations,and the mechanism of the water transport in PEFC is considered.
基金supported by the National Natural Science Foundation of China (No.50976011)Fundamental Research Funds for the Central Universities of China (No. 2009JBM090)
文摘Gas diffusion layer(GDL) plays a great important role in proton exchange membrane fuel cell(PEMFC).Water transport mechanism in GDL is still not clear.In the present study,an ex-situ transparent setup is built to visualize the transport phenomena and to measure the threshold pressure of water in GDL at different temperatures.It is found that the relationship between the breakthrough pressure and the temperature is nearly linear(i.e.the pressure decreases linearly with the increase of temperature).To avoid the problems faced by the continuum models,the pore network model is developed to simulate the liquid water transport through the carbon paper.A uniform pressure boundary condition is used in simulation and the results are similar to the ones obtained in the experiment.The reason is that the contact angle and surface tension coefficient of water in GDLs change accordingly with the change of temperature.
基金the National Natural Science Foundation of China (No.50776006,No.50976011)
文摘This paper studied the breakthrough pressure for liquid water to penetrate the gas diffusion layer(GDL) of a proton exchange membrane fuel cell(PEMFC).An ex-situ testing was conducted on a transparent test cell to visualize the water droplet formation and detachment on the surface of different types of GDLs through a CCD camera.The breakthrough pressure,at which the liquid water penetrates the GDL and starts to form a droplet,was measured.The breakthrough pressure was found to be different for the GDLs with different porosities and thicknesses.The equilibrium pressure,which is defined as the minimum pressure required maintaining a constant flow through the GDL,was also recorded.The equilibrium pressure was found to be much lower than the breakthrough pressure for the same type of GDL.A pore network model was modified to further study the relationship between the breakthrough pressure and the GDL properties and thicknesses.The breakthrough pressure increases for the thick GDL with smaller micro-pore size.
基金This work was financially supported by the Office of the Higher Education Commission under NRU Project of Thailandthe Research Network NANOTEC(RNN)program of the National Nanotechnology Center(NANOTEC),NSTDA,Ministry of Higher Education,Science,Research and Innovation(MHESI),Thailand.T.Sichumsaeng would like to thank the Science Achievement Scholarship of Thailand(SAST)for the support of her PhD study.
文摘We report the electrochemical performance of Ni(OH)_(2) on a gas diffusion layer(GDL).The Ni(OH)_(2) working electrode was successfully prepared via a simple method,and its electrochemical performance in 1 M NaOH electrolyte was investigated.The electrochemical results showed that the Ni(OH)_(2)/GDL provided the maximum specific capacitance value(418.11 F·g^(−1))at 1 A·g^(−1).Furthermore,the Ni(OH)_(2) electrode delivered a high specific energy of 17.25 Wh·kg^(−1) at a specific power of 272.5 W·kg^(−1) and retained about 81%of the capacitance after 1000 cycles of galvanostatic charge–discharge(GCD)measurements.The results of scanning electron microscopy(SEM)coupled with energy-dispersive X-ray spectroscopy(EDS)revealed the occurrence of sodium deposition after long-time cycling,which caused the reduction in the specific capacitance.This study results suggest that the light-weight GDL,which can help overcome the problem of the oxide layer on metal–foam substrates,is a promising current collector to be used with Ni-based electroactive materials for energy storage applications.
文摘The lattice Boltzmann method is applied to the investigations of the diffusivity and the permeability in the gas diffusion layer(GDL)of the polymer electrolyte fuel cell(PEFC).The effects of the configuration of water droplets,the porosity of the GDL,the viscosity ratio of water to air,and the surface wettability of the GDL are investigated.From the simulations under the PEFC operating conditions,it is found that the heterogeneous water network and the high porosity improve the diffusivity and the permeability,and the hydrophobic surface decreases the permeability.
基金partially supported by the grant subsidy of the "Nano Project" for Private Universities: 2011-2014 from MEXT, Japansupported by the "Advanced Science Research Laboratory" in Saitama Institute of Technology, Japan
文摘To study the effect of annealing temperature on the joints between magnesium and aluminum alloys, and improve the properties of bonding layers, composite plates of magnesium alloy（AZ31 B） and aluminum alloy（6061） were welded using the vacuum diffusion bonding method. The composite specimens were continuously annealed in an electrical furnace under the protection of argon gas. The microstructures were then observed using scanning electron microscopy. X-ray diffractometry was used to investigate the residual stresses in the specimens. The elemental distribution was analyzed with an electron probe micro analyzer. The tensile strength and hardness were also measured. Results show that the diffusion layers become wide as the heat treatment temperature increases, and the residual stress of the specimen is at a minimum and tensile strength is the largest when being annealed at 250 ℃. Therefore, 250 ℃ is the most appropriate annealing temperature.
基金support rendered through a Major Research Project No. F-31-51/2005(SR)
文摘In many circumstances,dissimilar metals have to be bonded together and the resulting joint interfaces must typically sustain mechanical and/or electrical forces without failure,which is not possible by fusion welding processes.The melting points of magnesium(Mg)and copper(Cu)have a significant difference(nearly 400℃)and this may lead to a large difference in the microstructure and joint performance of Mg-Cu joints.However,diffusion bonding can be used to join these alloys without much difficulty.This work analyses the effect of parameters on diffusion layer thickness,hardness and strength of magnesium-copper dissimilar joints.The experiments were conducted using three-factor,five-level,central composite rotatable design matrix.Empirical relationships were developed to predict diffusion layer thickness,hardness and strength using response surface methodology.It is found that bonding temperature has predominant effect on bond characteristics.Joints fabricated at a bonding temperature of 450℃, bonding pressure of 12 MPa and bonding time of 30 min exhibited maximum shear strength and bonding strength of 66 and 81 MPa, respectively.
基金the financial supports from the National Natural Science Foundation of China(No.51505323)State Key Laboratory of Advanced Welding and Joining,Harbin Institute of Technology,China(No.AWJ-17M-04).
文摘Ti-6Al-4V(wt.%) and Ti-22Al-25Nb(at.%) were joined by diffusion bonding at 950 ℃ and 15 MPa for 100 min, and the microstructure and mechanical properties of the resulting joints were investigated. The composition of the diffusion layer is B2/discontinuous α/α2 layer/necklace-shaped β+α’ layer, where the content of any element at a given point mainly depends on the distance of the point from the interface and the phase type at the point. The tensile strength of the joint is 894 MPa, which is almost the same as that of the Ti-22Al-25Nb base alloy. The fracture surfaces on both sides of the joint are composed of two main regions. One region displays a relatively flat surface and fractures along the bonding interface. The other is composed of a moderate number of irregularly-shaped cavities on the Ti-6Al-4V side and many irregularly-shaped bulges on the Ti-22Al-25Nb side. Both regions result from fracture along the boundaries between β+α’ layers and αp grains or from the transcrystalline fracture of αp grains.
基金supported by the Ministry of Knowledge Economy (MKE, Korea) under the Global Collaborative R&D program supervised by the KIAT (N0000698)
文摘This study shows the preparation of a TiO2 coated Pt/C（TiO2/Pt/C） by atomic layer deposition（ALD）,and the examination of the possibility for TiO2/Pt/C to be used as a durable cathode catalyst in polymer electrolyte fuel cells（PEFCs）. Cyclic voltammetry results revealed that TiO2/Pt/C catalyst which has 2 nm protective layer showed similar activity for the oxygen reduction reaction compared to Pt/C catalysts and they also had good durability. TiO2/Pt/C prepared by 10 ALD cycles degraded 70% after 2000 Accelerated degradation test, while Pt/C corroded 92% in the same conditions. TiO2 ultrathin layer by ALD is able to achieve a good balance between the durability and activity, leading to TiO2/Pt/C as a promising cathode catalyst for PEFCs. The mechanism of the TiO2 protective layer used to prevent the degradation of Pt/C is discussed.
基金Project(N N507 5898 38)supported by the Polish Ministry of Science and Higher Education and the National Science Center,Poland
文摘A diffusive titanium nitride layers were produced on AZ91 D magnesium alloy by a hybrid method which combines the titanium coating physical vapor deposition（PVD） with subsequent nitriding. The layers are composed of a thin surface zone of titanium nitrides and oxides, an intermediate titanium zone and Ti-Al-Mg type diffusive zone. Since the layers improve the corrosion resistance, the best corrosion resistance is obtained when the layers are produced on aluminum base sub-layer by oxynitriding.
基金The National Science Foundation of China under contract No.40572142the Doctoral Foundation of the Ministry of Education of China under contract No.20040423016.
文摘The diffusive boundary layer （DBL） is the zone for matter exchange between surface water and aquatic sediments. To elucidate the influence of DBL on salt release from saline sediments to freshwater, two experiments with or without wind blowing were conducted. According to the experiments, a 3.5 cm DBL is formed above the smoothed sediments at a steady wind field and this thickness is greater than other studies. The observed flux of salt through the DBL is 6% larger than the calculated value from Fick＇ s first law. The results indicate that molecular diffusion is the dominant mechanism for salt transport through the DBL. The presence of DBL suppresses the hydrodynamic enhancement for matter exchange between sediments and overlying water. Therefore, salts in the sediments of a polder reservoir may influence the water quality chronically.
基金Projects(51375070,51574058)supported by the National Natural Science Foundation of China
文摘Homogenization annealing of the 7050/6009 bimetal slab prepared by direct-chill casting was investigated and its effects on microstructural evolution, composition distribution and mechanical properties in the interfacial region of the bimetal were studied. The results show that the optimized homogenization annealing process was 460℃for 24 h. After homogenization annealing, the Zn-rich phases and Al15（FeMn）3Si2phases were precipitated at the interface of the bimetal. The diffusion layer thickness of homogenized bimetal increased by 30 μm from 440 to480℃for 24 h, while it increased by 280 μm from 12 to 36 h at 460℃. The Vickers hardnessesat 6009 alloy side and interface of the bimetal decreased after homogenized annealing and grain coarsening was considered asthedominating softening mechanism.The hardness variation at 7050 alloy side was complicated due to the combined action of solution strengthening, dispersion strengthening and dissolution of reinforced phases.
基金Project(51674303) supported by the National Natural Science Foundation of ChinaProject supported by National Youth Thousand Plan of China+2 种基金Project(2018RS3015) supported by Huxiang High-Level Talent Gathering Program of Hunan Province,ChinaProject(2019CX006) supported by Innovation Driven Program of Central South University,ChinaProject supported by the Research Fund of the Key Laboratory of High Performance Complex Manufacturing at Central South University,China
文摘Cu/Al multilayers were produced by high-temperature accumulative roll bonding(ARB)methods up to three passes.To achieve a high bonding strength,prior to ARB processing,the Cu and Al sheets were heated to 350,400,450 and 500 ℃,respectively.The mechanical properties were evaluated by tensile tests.The microstructure was examined by optical microscopy and scanning electron microscopy equipped with energy dispersive spectrometry.The ultimate tensile stress,the grain size and the thickness of diffusion layer of lamellar composites increase with rolling temperature.When the rolling temperature is 400 ℃,the laminates show the highest ductility,but the yield stress is the lowest.As the rolling temperature further increases,both the yield stress and the ultimate tensile stress increase and the ductility decreases slightly.The mechanical properties of lamellar composites processed by low and high temperature ARB are determined by grain size and the thickness of diffusion layer,respectively.
基金financially supported by the Major Program of National Natural Science Foundation of China (No. U1710254)Shanxi Province Science and Technology Major Projects (No.20181101008)+1 种基金the Scientific and Technological Progress of Shanxi Province Colleges and Universities (No.2017132)the National Natural Science Foundation of China (Nos.51974196, 51975398,and 51905372)。
文摘Corrugated cold roll bonding(CCRB) produces metal composite plate with improved mechanical properties compared with conventional methods,but the interfacial mechanism is not fully understood.Here,Cu/Al composite plate with good plate shape was produced by CCRB,and the bonding mechanism and strength along the corrugated interface were studied by experiments and finite element simulations.The results showed that the average bonding strength of Cu/Al composite plate produced by CCRB was nearly twice that of conventional composite plate at an average reduction of 40% during rolling.Strong friction shear stresses occurred at the interface of the corrugated composite plate,which promoted the plastic deformation of the metals and accelerated the rupture of the brittle interfacial layer.Electron backscattered diffraction analysis showed that higher degrees of grain elongation and refinement occurred in the matrices at the front waist and trough due to the stronger normal and shear stresses.Energy-dispersive spectroscopy line scans showed that the thickest atomic diffusion layer occurred at the front waist.The present combination of experimental and computational analyses provides insights into the underlying mechanism of mechanically improved metal composites prepared by CCRB.
文摘The effects of postweld heat treatment on the microstructure and metallurgical properties of a bronze–carbon steel(st37)explosively bonded interface were studied.Explosive welding was done under 1.5-and 2-mm standoff distances and different conditions of explosive charge.Samples were postweld heat treated for 4 and 16 h in the furnace at 250°C and 500°C and then air cooled.Laboratory studies using optical microscopy,scanning electron microscopy,and microhardness testing were used to evaluate the welded samples.Microstructural examinations showed that by increasing the standoff distance and the explosive charge,the interface of bronze to steel became wavier.The microhardness test result showed that the hardness of the samples was higher near the joint interface compared with other areas because of the intensive plastic deformation,which was caused by the explosion force.The results show that increasing the heat treatment temperature and time caused the intermetallic compounds’layer thickness to increase,and,because of the higher diffusion of copper and tin,the iron amount in the intermetallic compounds decreased.Also,because of the increase in heat treatment temperature and time,internal stresses were released,and the interface hardness decreased.
