- Ei，ESCI收录期刊
- 中国科学引文数据库(CSCD)核心期刊
- 中文核心期刊
- 文摘与引文数据库(Scopus)
- 剑桥科学文摘(CSA)
Membrane electrode assembly (MEA) is the core component of proton exchange membrane fuel cell (PEMFC), which provides the microchannels for the transfer of multiphase substances and electrochemical reaction sites. To achieve the commercialization of PEMFC, fabricating MEA with high power density, low Pt loading and good durability is needed. Inside MEA, the structures of function layers and the interfaces between layer to layer all have great impact on the performance of MEA outside of the catalyst. The MEA prepared by traditional methods (CCS method and CCM method) has many structural defects, which greatly reduces the utilization rate of Pt and the mass transfer ability. By optimizing the structure of each functional layer to eliminate defects, it will be beneficial to further improve the comprehensive performance of PEMFC. Based on the problems existing in the traditional MEA structure, literatures in recent years on the improvement of the structure of CL, PEM and GDL were combed, and the preparation methods, structure-activity relations, and advantages/disadvantages of each advanced structure were summarized. This paper will provide a guidance for the development of MEA with high performance, low cost and long service life in the future.
The synthesis of graphene-like carbon nitride has been a new research hotspot in the field of two-dimensional functional materials due to its similar structural characteristics to graphene and outstanding properties covering photocatalysis and lubrication and so on. Herein, the research progress of the microwave irradiation synthesis of graphene-like carbon nitride was discussed. Based on the comparison to the traditional preparation approaches including high-temperature oxidation corrosion, liquid phase ultrasonic exfoliation and thermal polymerization, etc., the advantages of microwave irradiation synthesis were analyzed. At the same time, one can find that by means of using high-energy microwave instrument and microwave absorbents covering graphite powders and short carbon fibers that possess excellent microwave energy absorption ability, the transferring and absorption efficient of energy as well as the non-steady degree of the synthesis reactions occurred in the microwave electromagnetic field can be enhanced, is consequently beneficial to the achievement of novel products with special morphology and structure.
Based on the domestic third generation SiC fiber, the SiC fiber bundle reinforced composites with different interface thicknesses and matrix volume fractions were fabricated by chemical vapor infiltration, and the tensile behavior of the composites was investigated. Meanwhile, the influence of interface thickness and matrix volume fraction on the thermal residual stress of the SiC fiber bundle reinforced composites was analyzed by FEM.The FEM results indicate that the radial and hoop thermal residual stresses are obvious at the interface; the two kind of stresses are decreased with the increasing of the interface thickness and are increased with the increasing of the matrix volume fraction.The tensile tests results show that with the increasing of interface thickness, the tensile strength of the SiC fiber bundle reinforced composites tends to increase, and the fiber pull-out length also is increased correspondingly; but under the same interface thickness condition, a high volume fraction of the matrix will lead to the degradation of the tensile strength and toughness of the composites.
Electrospun fibrous membranes have been widely used for research of lithium-ion battery separators because of the high porosity, large specific surface area as well as excellent electrolyte wettability. However, little research has been focused on the puncture strength, which influences the safety of lithium-ion battery seriously. PPESK fibrous membranes with different thicknesses were fabricated by electrospinning technique, and the mechanical properties were improved by heat treatment, and the puncture strength of heat-treated PPESK membrane was tested using universal tensile testing machine and the linear relationship between the puncture strength of heat-treated PPESK fibrous membrane and the thickness was established. The further microscopic analysis of the puncture failure region was carried out to explore the puncture failure mechanism of heat-treated PPESK fibrous membranes. The result shows that the puncture process of isotropic heat-treated PPESK fibrous membrane is much tempered compared with PP microporous separator. The penetration of the heat-treated PPESK fibrous membranes was caused by the bend, deformation and fracture of PPESK fibers. The failure region of heat-treated PPESK fibrous membrane appears a circular hole, while the PP separator is long cracks. The puncture mechanism of heat-treated PPESK fibrous membrane is beneficial to prevent the destruction of lithium dendrites, but the puncture strength of heat-treated PPESK fibrous membrane remains to be enhanced.
K49 and F-Ⅲ two kinds of different structure aramid fibers and their 5224A epoxy matrix composites were selected. The tension strength of single fiber, FTIR, XPS, DSC, SEM, mechanical and dielectrical properties was used to characterize the physicochemical properties of fibers and structure/wave-transmitting properties of composites. It is found that different fibers result in different changes under the same solar radiation condition. The obvious "self-shield" phenomenon is observed in K49 fibers, but there's no proof that F-Ⅲ has the same ability. A tension strength conservation rate of 82% is obtained after 400 hours solar radiation. F-Ⅲ fibers, by contrast, are sensitive to solar radiation and a conservation rate of 50% is obtained at the same condition. The decreased tension strength is due to physicochemical degradation on the surface of the fibers and the decrease of crystallinity degree. It is proved that solar radiation has no obvious effect on the properties of composites. The flexibility, ILSS and dielectric properties has little change. The tensile strength is slightly improved, and the compression strength is slightly decreased. A decrease of 11.8% is obse-rved on K49/5224A composites and 6.6% for that of F-Ⅲ/5224A. It is because of that the degrad-ation occurred on the surface of composites.
Comprehensive high-performance epoxy nanocomposites were successfully prepared by co-incorporating 2-dimensional montmorillonite (MMT) and 0-dimensional nano TiO2 co-incorporated into epoxy. Mechanical tests and thermal analyses show that the resulting epoxy/MMT/nano TiO2 nanocomposites obtained are obviously superior to pure epoxy, epoxy/MMT nanocomposites, and epoxy/nano TiO2 nanocomposites in tensile modulus, tensile strength, flexural modulus, flexural strength, notch impact strength, glass transition temperature, and thermal decomposition temp-erature. X-ray diffraction and transmission electron microscopy inspection reveal that in the epoxy/MMT/nano TiO2 nanocomposites, the MMT is completely exfoliated into 2-dimensional nanoscale mono-platelets, which is intermingled with the 0-dimensional nano TiO2 spheres in epoxy resion. This study shows is that co-incorporating two proper, dimensionally different nanomaterials into polymer matrices could be a successful pathway in preparing comprehensive high-performance polymer nanocomposites.
The high concentration graphene aqueous dispersion was obtained by high-pressure homogenization liquid phase exfoliation (HPH-LPE) of flake graphite in water. The effect of surfactant concentration, HPH pressure and cycle number on the concentration of graphene dispersion CG was studied by UV-Vis spectra. The structure and morphology of graphene were analyzed by Roman spectra, SEM and TEM. The results indicate that CG is obtained up to 324.3mg·L-1 for the first time by the parameters optimization, which is 10 times higher than that obtained by sonication; graphene obtained has few defects, thin thickness and large size, indicating the good quality of graphene production; the conductivity of free-standing film prepared by the obtained graphene dispersion can reach 3.2×104S·m-1.
The high contact resistance between graphene and metal retards the application of graphene in micro-and nano-electronics. Boron (B) doping can effectively reduce the contact resistance of graphene. The influence of dopant concentration on the adsorption of multilayer gold (Au) atoms on B-doped graphene was studied using the first principles theory. Firstly, the binding energy of B-doped graphene with various B concentrations was calculated, and the stability of each B-doped graphene was verified. Then, after structural optimization of B-doped graphene, multilayer Au atoms were introduced into graphene and the adsorption energy, pseudogap, local density of state, charge density distribution, and charge transfer of the adsorption system were analyzed. The B concentrations considered were respectively 1.39%, 4.17%, 6.94%, 9.72%, 12.50% and 15.28%. The results show that as B concentration increases, the pseudogap of the adsorption system becomes wider and the adsorption energy rises, leading to a more stable adsorption system. Also, an obvious hybridization between B and Au atoms takes place. This elevates the charge density and promotes the charge transfer at the interface of graphene and Au, which can help reduce the contact resistance between them. However, when the concentration reaches 15.28%, the geometric deformation of graphene becomes intolerable due to a high doping concentration.
A facile one-pot hydrothermal route was selected for the synthesis of ZnCo2O4 and ZnCo2O4/rGO composite electrode materials. The structure, morphology and electrochemical properties of the as-perpared materials were characterized by XRD, SEM and RST5000 electrochemical workstation. ZnCo2O4 electrode materials with a group of radial structure, folding lamellar structure and the spherical structure were obtained by changing the hydrothermal temperature. Results show that after the addition of graphene, ZnCo2O4 exhibits regular polygonal structure and is attached to graphene sheets. Their synergistic effect can effectively improve the electrochemical performance of electrode materials. When the mass ratio of zinc cobaltate to graphene oxide is 6:1, the specific capacitance of ZnCo2O4/rGO composite material is 205F/g, which is 114% higher than that of pure ZnCo2O4.
The precursor alloy with atomic fraction is Ni30-xFexMn70(x=0, 10, 20) by means of vacuum melting and solid solution, using the method of dealloying to nanoporous Ni and Ni-Fe alloy, with XRD, SEM phase compositions and microstructure were analyzed.The electrocatalytic performance for hydrogen evolution reaction was investigated by linear sweep voltammetry(LSV), electrochemical impedance spectroscopy(IMP), square wave potential technique(SWPT) and chrono potentiometry(CP).The results show that the nanoporous Ni-Fe alloy with lamellar structure is obtained by adding Fe, which improves the surface area of nanoporous Ni, and synergistic effect between Fe and Ni is produced, which can effectively improve the electrocatalytic activity of hydrogen evolution of the alloy.When the atom fraction of Fe is 10%, the surface area of nanoporous Ni-Fe alloy obtained by dealloying is the largest, and the electrocatalytic performance of hydrogen evolution is the best. Under the current density of 0.1A/cm2, hydrogen evolution overpotential is only 56mV, after continuous electrolysis for 10h, the alloy exhibits the high electrocatalytic activity and good electrochemical stability.
Three kinds of superparamagnetic iron oxide nanoparticles (SPIONs) with different particle sizes prepared by polyol pyrolysis, and the SPIONs contained Fe3O4 crystal phase with average particle sizes of 8.73, 12.57nm and 15.25nm. The nanoparticles have relatively uniform size distribution and good dispersion property and samples were all superparamagnetic at 300K. The aqueous dispersion of SPIONs with different particle sizes and concentrations were treated in alternating current magnetic field(ACMF) with a frequency of 425kHz and a magnetic field amplitude of 5.3kA·m-1 to conduct heating experiments.The relationship between the specific absorption rate (SAR) and the particle sizes of the samples were discussed. The Brownian relaxation time and Neel relaxation time were calculated. The results show that the heating rate of the aqueous samples increases with the increase of the particle sizes. When the initial temperature is 20℃, the increments of the temperature of 25, 27℃ and 35℃ in 480 seconds are measured for the three nanoparticle solutions (2mg·mL-1) with nanoparticle sizes of 8.7, 12.6nm and 15.3nm, respectively. The Neel relaxation time is shorter than the Brownian relaxation time, indicating that Neel relaxation dominates heating in this system. The larger the particle size is, the higher the SAR value will be, and the highest SAR value is 810W·g-1. The SAR value is negatively correlated with the concentration of the aqueous dispersion.
Nano Ni0.5Zn0.5Fe2O4 powders were prepared by the coprecipitation method combined with sol-gel method. The microstructure and electromagnetic performance of the as-prepared four kinds of Ni0.5Zn0.5Fe2O4 samples with different addition proportion were characterized by X-ray diffraction, atomic force microscope (AFM), vector network analysis (VNA). The results show that the pure Ni0.5Zn0.5Fe2O4 is gained in each proportion under 650℃ calcination. The Ni0.5Zn0.5Fe2O4 particles are spherical, with the increase of adding proportion in coprecipitation process, particle size decreases first and then increases, the particles have the minimum size while the proportion is 60%, the average size is around 44nm. In the range of 2-12.4GHz, the greater the thickness of the material, the closer the effective absorption band of Ni0.5Zn0.5Fe2O4 is to the low frequency band, the maximum absorbing intensity of Ni0.5Zn0.5Fe2O4 can reach -24.94dB. While the proportion is 60%, the effective absorption band of Ni0.5Zn0.5Fe2O4 is 5.0-9.9GHz, the bandwith reaches maximum, and microwave absorption property is the best.
TiO2 nanotubes arrays with dominant (001) facets were fabricated by multi-anodic oxidation technology. The influence factor of the electrolyte composition on the ratio of different facets for anatase TiO2 and the bioactivity were investigated. Besides, the characterization of the surface morphologies and crystal structures were analyzed by scanning electron microscope (SEM) and X-ray diffraction (XRD), etc. Finally, the bioactivity was estimated by the CaP salt deposition vis biomin-eralization process and protein adsorption experiment. The results show that the relative proportions of different facets in the TiO2 nanotubes can be adjusted by changing the content of H2O in the electrolyte. The (004) facet texture coefficient of TiO2 nanotubes arrays prepared in 2% H2O(volume fraction) electrolyte reaches up to 4.76. The TiO2 nanotubes with dominant (001) facets can accelerate the deposition of hydroxyapatite and raise the amount of protein adsorption in the humanoid environment by providing more active sites for biomineralization and protein adsorption. The TiO2 nanotubes with a higher proportion of (001) facets have the more excellent biological activity.
Cu-doped TiO2 nanoparticles were synthesized through sol-gel method.X-ray diffraction(XRD), transmission electron microscopy (TEM), scanning transmission electron microscope (STEM), X-ray photoelectron spectroscopy(XPS) and UV-Vis absorption spectrum(UV-Vis) were used to characterize the phase composition, average grain size, morphology of TiO2 nanoparticles, chemical valence states and the optical absorption property of TiO2 nanoparticles. The results show that Cu doping suppresses the phase transition of TiO2. CuO appears on the surface of TiO2 particles at 650℃, and the doped Cu ions are in the form of Cu+. The light absorption bands of Cu-doped TiO2 are red-shifted markedly. The absorbance of the sample increases with the increase of Cu doping amount, and the UV-Vis absorption band is red shifted with the increase of temperature.
The isothermal compression tests of Ti-2.7Cu alloy were tested to study the hot deformation behavior in temperature range of 740-890℃ and strain rate range of 0.001-10s-1 on a Gleeble-3500 thermomechanical simulator. Constitutive model based on strain compensation was established by the Arrhenius hyperbolic sine function equation, and set up a constitutive equation for PSO-BP neural network. The results show that the flow stress is more sensitive to deformation temperature and strain rate, the flow stress is decreased with the increase of deformation temperature and decrease of strain rate; the flow stress curves present stable states in high temperature and low strain rate. For a constitutive equation based on strain compensation, the data points with the predicted error less than 15% account for 85.28% of all test data by error calculation; and for the constitutive equation based on PSO-BP neural network, the data points with the predicted error less than 15% account for 96.67% of all test data. PSO-BP neural network model has higher accuracy, it can better predict the flow stress of Ti-2.7Cu at elevated temperature.
Directionally solidified nickel-based superalloy DZ444 specimens with different directions were selected. The crystal orientation and microstructure were characterized by electron back-scattered diffraction technique and so on. The longitudinal wave velocity and attenuation coefficient were analyzed by ultrasonic pulse-echo technique. Results show that the above two acoustic properties are anisotropic. With the included angle φ between the normal direction of the sheet plane and the solidified direction increases from 0° to 45° to 90°, the longitudinal wave velocity increases from 5533m/s to 6595m/s and then decreases to 5634m/s, while the attenuation coefficient shows a monotonic increment of 0.19dB/mm. Further spectrum analysis shows that the main frequency shift, amplitude shift and apparent integral reflection coefficient of the surface echo and the bottom echo present a similar trend with the attenuation coefficient. This is mainly resulted by the difference of microstructure and crystal orientation.
To improve the poor toughness of traditional particulate reinforced composites, microstructurally toughened composites with WC/H13 as reinforced region and Inconel625 as toughened region were prepared by laser cladding. The microstructure of composites and impact fracture were analysed by optical microscopy, ultra-depth 3D microscope and scanning electron microscopy. The impact toughness and wear property of composites were investigated by Charpy impact testing machine and friction-abrasion testing machine. The results show that the reinforced region of 20% (volume fraction, the same below)WC/H13 is reinforced by WC particles and M6C carbides while the toughened region of Inconel625 alloy is mainly composed of columnar dendrite crystals and precipitated phases. The average hardness of Inconel625 is 230.5HV, while the hardness of WC/H13 is gradually increased to 402HV from the interface to the center area. The average impact energy of microstructurally toughened composites is 13.8J/cm2, which is 5.5 times of traditional 10% WC/H13. In the condition of dry sliding wear at room temperature, the wear resistance of microstructurally toughened composites is comparable to traditional 10% WC/H13 and 5 times of quenched H13 steel. The average friction coefficient of microstructurally toughened composites is 81% of traditional 10% WC/H13 and 80% of quenched H13 steel, which indicates excellent anti-wear and wear resistant property. By microstructurally toughening, the impact toughness of particulate reinforced composites can be substantially improved with excellent wear resistant property ensured.
Three kinds of pre-treatment process were carried out in a twin roll cast 3003 Al alloy sheet. The evolution of grain structure and recrystallization texture was investigated in the pre-treated sheet after cold-rolling and annealing at 380-500℃. The results show that the optimized pre-treatment is determined to be 610℃ for 12h followed by 460℃ for 12h. Second phase particle coarsening occurs at high temperature stage and the Mn concentration in solid solution decreases at low temperature stage, both of them can promote the recrystallization nucleation rate during the subsequent annealing. During annealing at 500℃, particle stimulated nucleation occurs in the vicinity of the coarse second phase, leading to a reduced texture intensity; in addition, precipitation is hardly found to occur during annealing and hence the inhibition of recrystallization nucleation is negligible, and finally the recrysta-llization structure with fine grains together with weakened texture is obtained.
Using self-piercing riveting (SPR), the joinability of dissimilar sheet combinations in TA1 pure titanium (TA1) and 1420 aluminium-lithium (AL1420) alloy sheets were studied. SPR joints of TA1/AL1420 (TAF), AL1420/TA1 (ATF) and TA1/AL1420 (TAS) were fabricated from different rivets in the hardness of ≥ 44HRC and ≥ 46HRC, correspondingly. High cycle fatigue tests were conducted based on tensile-shear tests. Then F-N curves of different joints were fitted. Furthermore, fretting wear mechanisms of SPR joints were analysed by scanning electron microscopy (SEM) and energy disperse spectroscopy (EDS). Results show that the fatigue strength of ATF joints is better than that of the other joints. And the fatigue strength of TAS joints is superior to TAF joints at middle and high load level. Fatigue failure of all joints initiates in fretting wear areas, and fatigue wear results in fatigue crack initiation. Fretting degree is an important factor for affecting fatigue strengths. The serious fretting wear areas are different at different load levels, and then the initiated areas of fatigue cracks are different. Finally, different failure modes occur in the same SPR joints.
In order to study the effect of hybrid structure on the mechanical properties of aluminum matrix composites. The gas-atomized Al2024 powders were mechanically blended with Ti-10% (mass fraction) B4C powders by ball milling for different time, and then compacting the powders via hot press sintering and hot extrusion to fabricate the hybrid structured Ti-B4C/Al2024 composite. The microstructure and mechanical properties of different materials were observed and tested by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and tensile testing machine. The strengthening and toughening behavior of hybrid structured composites were further discussed. The results show that the hybrid structured Ti-B4C/Al2024 composite consists of Al2024 matrix, core-shell structured Ti/Al18Ti2Mg3 and B4C particles. With the addition of 5% Ti-B4C hybrid powder after ball milling for 6h, the yield strength increases from 107MPa to 122MPa, and the composite exhibits almost the same elongation as that of the hot extruded Al2024 alloy. When the milling time is extended to 12h, the elongation of the sample 5TB-12h can reach 16.4%. However, the elongation of the composites decreases with the increase of Ti-B4C.
SiCp/Al composites were prepared by pressureless infiltration using domestic abrasive grade SiC particles with average diameters in the range of 60-80μm. Ultrasonic cleaning method was used to investigate the effect of the surface adsorbate of SiC particles on the infiltration process and mechanical property of the SiCp/Al composite. The results show that all types of the studied SiC particles are adhered by low mass fractions of the adsorbate(< 0.5%), comprising mainly fine SiC particles(< 5μm)and, in certain cases, low fraction of carbon. That surface adsorbate has a negative effect on the wettability between SiC particles and molten alloy, resulting in the reduced density and mechanical property of the infiltrated SiCp/Al composite. Ultrasonic cleaning process can effectively wipe off the adsorbate, and, by using the cleaned SiC particles, the success rate of the infiltration can be raised from 25% to 100%. Correspondingly, the flexure strength and elasticity modulus of the composites are improved from 320MPa to 390MPa and from 203GPa to 232GPa, respectively.
Fe-Cr-Ni alloys are widely applied to aero-engine, industrial gas turbine and other equipment because of their high temperature strength and toughness and creep resistance. Four kinds of porous MgO reinforced Fe-Cr-Ni matrix composites, which are nano-MgO (34.9%)/Fe-Cr-Ni (mass fraction, the same below), micro-MgO (34.9%)/Fe-Cr-Ni, micro-MgO (25.7%)/Fe-Cr-Ni, micro-MgO (17.0%)/Fe-Cr-Ni, were prepared by powder sintering and in situ synthesis method. Effect of the particle sizes and content of MgO on bending strength at room or high temperature and oxidation resistance of porous metal matrix composites at high temperature were investigated by XRD, DTA and SEM. The results show that different raw materials lead to the different enthalpy, resulting in the different porosities and phase compositions for the sintered samples. The porous composites consist of Cr0.7Fe0.36Ni2.9, Cr-Fe and MgO phases generally. The bending strength of these porous composites decreases with the increase of the temperature. The high temperature oxidation resistance of nano-MgO (34.9%)/Fe-Cr-Ni composites is the best of the four kinds of porous composites.
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