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A comprehensive assessment on the durability of gas diffusion electrode materials in PEM fuel cell stack

Arunkumar JAYAKUMAR

《能源前沿（英文）》 2019年 第13卷 第2期   页码 325-338 doi: 10.1007/s11708-019-0618-y

摘要： Polymer electrolyte membrane (PEM) fuel cell is the most promising among the various types of fuel cells. Though it has found its applications in numerous fields, the cost and durability are key barriers impeding the commercialization of PEM fuel cell stack. The crucial and expensive component involved in it is the gas diffusion electrode (GDE) and its degradation, which limits the performance and life of the fuel cell stack. A critical analysis and comprehensive understanding of the structural and functional properties of various materials involved in the GDE can help us to address the related durability and cost issues. This paper reviews the key GDE components, and in specific, the root causes influencing the durability. It also envisages the role of novel materials and provides a critical recommendation to improve the GDE durability.

关键词： PEM fuel cell     gas diffusion electrode(GDE)     gas diffusion layer(GDL)     membrane electrode assembly     durability     fuel cell catalyst    

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Molecular diffusion in ternary poly(vinyl alcohol) solutions

《化学科学与工程前沿（英文）》 2022年 第16卷 第6期   页码 1003-1016 doi: 10.1007/s11705-021-2121-3

摘要： The diffusion kinetics of a molecular probe—rhodamine B—in ternary aqueous solutions containing poly(vinyl alcohol), glycerol, and surfactants was investigated using fluorescence correlation spectroscopy and dynamic light scattering. We show that the diffusion characteristics of rhodamine B in such complex systems is determined by a synergistic effect of molecular crowding and intermolecular interactions between chemical species. The presence of glycerol has no noticeable impact on rhodamine B diffusion at low concentration, but significantly slows down the diffusion of rhodamine B above 3.9% (w/v) due to a dominating steric inhibition effect. Furthermore, introducing surfactants (cationic/nonionic/anionic) to the system results in a decreased diffusion coefficient of the molecular probe. In solutions containing nonionic surfactant, this can be explained by an increased crowding effect. For ternary poly(vinyl alcohol) solutions containing cationic or anionic surfactant, surfactant–polymer and surfactant–rhodamine B interactions alongside the crowding effect of the molecules slow down the overall diffusivity of rhodamine B. The results advance our insight of molecular migration in a broad range of industrial complex formulations that incorporate multiple compounds, and highlight the importance of selecting the appropriate additives and surfactants in formulated products.

关键词： fluorescence correlation spectroscopy     poly(vinyl alcohol)     anomalous diffusion     crowding effects     dynamic light scattering     binding effects     rhodamine B    

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evaluation of renal function using diffusion weighted imaging and diffusion tensor imaging in type 2

null

《医学前沿（英文）》 2014年 第8卷 第4期   页码 471-476 doi: 10.1007/s11684-014-0365-8

摘要：

This work aims to estimate the value of diffusion weighted imaging (DWI) and diffusion tensor imaging (DTI) in detecting early-stage kidney injury in type 2 diabetic patients with normoalbuminuria (NAU) versus microalbuminuria (MAU) prospectively. A total of 30 T2DM patients with normal kidney function were recruited and assigned to the NAU group (n = 14) or MAU group (n= 16) according to 8 h overnight urinary albuminuria excretion rate (AER) results. A contemporary cohort of health check-up recipients were included as controls (n = 12). DWI and DTI scans were performed on bilateral kidney using SE single-shot EPI, and apparent diffusion coefficient (ADC) and fractional anisotropy (FA) of the renal parenchyma was determined from ADC and FA maps of the three groups. ADC and FA values were compared among the three groups. According to DWI with a b value of 400 s/mm2, the MAU and NAU groups showed significantly lowered mean ADC values compared with the healthy controls (P<0.01). The mean ADC in the MAU group [(2.22±0.07)×10–3 mm2/s] was slightly lower than that of the NAU group [(2.31±0.22)×10–3 mm2/s], but this difference was not statistically significant (P>0.05). The FA value in the MAU group was higher than that in the control group (0.45±0.07 vs. 0.39±0.03, P = 0.004) but did not differ from that in the NAU group (0.42±0.03) (P>0.05). ADC and FA values may be more sensitive than urine AER in reflecting early-stage kidney injury and, hence, may facilitate earlier detection and quantitative evaluation of kidney injury in T2DM patients. Combined evaluation of ADC and FA values may provide a better quantitative approach for identifying diabetic nephropathy at early disease stages.

关键词： type 2 diabetes mellitus     microalbuminuria     diffusion weighted imaging     diffusion tensor imaging     early-stage kidney injury    

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Coupled diffusion of chloride and other ions in saturated concrete

Nattapong DAMRONGWIRIYANUPAP, Linyuan LI, Yunping XI

《结构与土木工程前沿（英文）》 2011年 第5卷 第3期   页码 267-277 doi: 10.1007/s11709-011-0112-z

摘要： Corrosion of reinforcing steel due to chloride ions is one of the severe deterioration problems in long-term performance of reinforced concrete structures. The deterioration process is frequently found in marine concrete structures, highway pavements, and bridges exposed to deicing salts. The diffusion of chloride ions is associated and strongly affected by other ions in the pore solution in concrete. In this paper, chloride penetration into concrete structures was mathematically characterized by the Nernst-Planck equation which considered not only diffusion mechanism of the chloride ions but also ionic interaction among other ions coming from externally applied deicers and within the Portland cement paste. Electroneutrality was used to determine the electrostatic potential induced by the ionic interaction. The material models of chloride binding capacity and chloride diffusion coefficient were incorporated in the governing equations. The governing equations were solved by using finite element method. A numerical example was used to illustrate the coupling effect of multi-ionic interactions and the effect of influential parameters. The numerical results obtained from the present model agreed very well with available test data.

关键词： diffusion     chloride     concrete     Nernst-Planck equation     durability    

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Magnetohydrodynamic slip flow and diffusion of a reactive solute past a permeable flat plate with suction

Krishnendu BHATTACHARYYA, G. C. LAYEK

《化学科学与工程前沿（英文）》 2011年 第5卷 第4期   页码 471-476 doi: 10.1007/s11705-011-1130-z

摘要： The magnetohydrodynamic (MHD) boundary layer slip flow and solute transfer over a porous plate in the presence of a chemical reaction are investigated. The governing equations were transformed into self-similar ordinary differential equations by adopting the similarity transformation technique. Then the numerical solutions are obtained by a shooting technique using the fourth order Runge-Kutta method. The study reveals that due to the increase in the boundary slip, the concentration decreases and the velocity increases. On the other hand, with an increase in the magnetic field and mass suction, both boundary layer thicknesses decreased. As the Schmidt number and the reaction rate parameter increases, the concentration decreases and the mass transfer increases.

关键词： slip flow     MHD boundary layer     reactive solute diffusion     flat plate     suction/injection    

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Chloride diffusion in concrete with carbonated recycled coarse aggregates under biaxial compression

《结构与土木工程前沿（英文）》 2023年 第17卷 第4期   页码 637-648 doi: 10.1007/s11709-023-0902-0

摘要： Chloride attack on concrete structures is affected by the complex stress state inside concrete, and the effect of recycled aggregates renders this process more complex. Enhancing the chloride resistance of recycled concrete in a complex environment via carbonization facilitates the popularization and application of recycled concrete and alleviates the greenhouse effect. In this study, the chloride ion diffusion and deformation properties of recycled concrete after carbonization are investigated using a chloride salt load-coupling device. The results obtained demonstrate that the chloride ion diffusivity of recycled concrete first decreases and then increases as the compressive load increases, which is consistent with the behavior of concrete, in that it first undergoes compressive deformation, followed by crack propagation. Carbonation enhances the performance of the recycled aggregates and reduces their porosity, thereby reducing the chloride diffusion coefficient of the recycled concrete under different compressive load combinations. The variation in the chloride ion diffusivity of the carbonized recycled aggregate concrete with the load is consistent with a theoretical formula.

关键词： recycled concrete     carbonated recycled coarse aggregate     biaxial compression     chloride diffusion     stress level    

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Experimental study of humid air reverse diffusion combustion in a turbulent flow field

GE Bing, ZANG Shusheng, GU Xin

《能源前沿（英文）》 2007年 第1卷 第4期   页码 428-434 doi: 10.1007/s11708-007-0062-6

摘要： Experiments were performed to investigate the differences between the propane/air turbulent diffusion reactive flows past bluff-body and the propane/humid air turbulent diffusion reactive flows in the same conditions. The velocity

关键词： propane/humid     propane/air turbulent     bluff-body     turbulent diffusion    

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Fuel variability effect on flickering frequency of diffusion flames

Jizhao LI, Yang ZHANG

《能源前沿（英文）》 2009年 第3卷 第2期   页码 134-140 doi: 10.1007/s11708-009-0034-9

摘要： It is known that fuel variability of different gas suppliers may cause combustion instability in a gas turbine combustor. Mechanisms that control the time scale of the heat release oscillations and acoustic pressure perturbations are both physical and chemical in nature, and thus can be influenced by changes in fuel composition. The intent of this study is to investigate the fuel variability on the flickering frequency of diffusion flames in the hope of understanding some of the fundamental aspects of fuel variability effect on the dynamics of combustion. Experiments were conducted at atmospheric pressure with a matrix of methane and propane blends. An optical fibre system was applied to capture simultaneously the flame flickering at two different light frequencies (430 nm and 516 nm), which provided a means of comparing the chemistry change. It was found that the low frequency oscillation of flow and flame structures depended only weakly on the exit velocities of the fuel, while ambient conditions had a significant effect on flickering frequencies and spectrum. The results of using CH and C H as test fuels at different flow rates showed very little variations, with peak frequencies at 11-13 Hz. When the jet flame was not disturbed, harmonics to at least the third mode were obtained in most of these cases. However, the cases which included CH /C H splits of 90/10, 85/15 and 80/20 by volume showed that unstable flickering frequencies and flame harmonics were not observed. When a mixture of methane/propane at a ratio of 1:1 was used the peak flickering frequency was around 6 Hz, and slight disturbance in the environment would cause the harmonics to disappear. Mechanisms thought to produce changes in the dynamic response and frequency harmonics were discussed.

关键词： fuel variability     flickering frequency     diffusion flames     dynamics of combustion    

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Transient process of methane-oxygen diffusion flame-street establishment in a microchannel

《能源前沿（英文）》 2022年 第16卷 第6期   页码 988-999 doi: 10.1007/s11708-021-0755-y

摘要： “Flame-street” is an interesting diffusion flame behavior in which a series of flame-segments is separately distributed along the mixing layer in a narrow channel. This experimental phenomenon was experimentally and numerically investigated with the focus on the steady-state, thermo-chemical flame structures in previous literature. In the present paper, the dynamic formation process of a methane-oxygen diffusion flame-street structure was simulated with a reacting flow solver developed based on the open-source framework OpenFOAM. By imposing a certain amount of ignition-energy near the channel outlet, a reaction-kernel was formed and bifurcated. Subsequently, three separate flames were consecutively generated from this kernel and propagated within the channel. The whole process was completed within 15 ms and all the discrete flames were eventually in a steady-state. Interestingly, different propagation features were observed for the three flame segments: The leading flame experienced a flame shape/type change from a tribrachial structure in its fast-propagating phase to a long, trailing diffusion tail after being anchored to the inlet. The successive flame had a much lower propagation speed, keeping its two wing-like (fuel-lean premixed and fuel-rich premixed) structure while moving toward its stabilization location, which was approximately in the middle of the channel. The last flame, after the ignition source was turned-off, was immediately convected a bit downstream, and eventually featured a similar two-branch-like structure as the second one. Moreover, chemical insights for the premixed and diffusion branches of the leading flame were also provided with the change of significance of some key elementary reactions focused on, in order to attain a detailed profiling of the flame-type transition. This paper is a first-ever one discussing the transient formation of flame-streets in literature and is believed to be useful for obtaining a comprehensive understanding of this unique flame characteristics from a dynamic point of view.

关键词： micro-combustion     flame-street     diffusion flame     mixing layer     flame propagation speed    

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Preparation of a Pb loaded gas diffusion electrode and its application to CO

Ang LI, Hua WANG, Jinyu HAN, Li LIU

《化学科学与工程前沿（英文）》 2012年 第6卷 第4期   页码 381-388 doi: 10.1007/s11705-012-1216-2

摘要： A Pb loaded gas diffusion electrode was fabricated and used for the electroreduction of CO to formic acid. The Pb/C catalyst was prepared by isometric impregnation. The crystal structure and morphology of the Pb/C catalyst were characterized by X-ray diffraction (XRD) and transmission electron microscope (TEM). The preparation conditions of the gas diffusion electrode were optimized by adjusting the amounts of polytetrafluoroethylene (PTFE) in the gas diffusion layer and acetylene black in the catalytic layer. The electrochemical performance of the as-prepared gas diffusion electrode was studied by chronoamperometry and cyclic voltammetry. The optimized gas diffusion electrode showed good catalytic performance for the electroreduction of CO . The current efficiency of formic acid after 1 h of operation reached a maximum of 22% at -2.0 V versus saturated calomel electrode (SCE).

关键词： electroreduction     carbon dioxide     lead catalyst     gas diffusion electrode     formic acid    

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Determination of the diffusion of poly(ethylene glycol) in polypropylene using ATR-FTIR

Hanjia CHEN, Xuhua SHI, Yafei ZHU, Yi ZHANG, Jiarui XU,

《化学科学与工程前沿（英文）》 2010年 第4卷 第3期   页码 336-341 doi: 10.1007/s11705-009-0230-5

摘要： The diffusion of poly(ethy1ene glycol) (PEG) in polypropylene (PP) was investigated using attenuated total reflectance Fourier Transform Infrared Spectroscopy (ATR-FTIR), Atomic Force Micrograph (AFM), and Scanning Electron Microscopy (SEM). It has been found that the diffusion of PEG in PP was greatly affected by the annealing temperature and the molecular weight of PEG. Higher temperature was in favor of PEG to diffuse in PP with fast velocity and reached diffusion equilibrium with shorter time. PEG with higher molecular weight was distributed in PP with bigger phase domains and had lower diffusivity, which resulted in its lesser enrichment on the surface of the PP blend film.

关键词： diffusion     polypropylene     molecular     diffusion equilibrium     attenuated    

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Reverse electrodialysis heat engine with helium-gap diffusion distillation: Energy efficiency analysis

《能源前沿（英文）》 doi: 10.1007/s11708-024-0947-3

摘要： The depletion of energy resources poses a significant threat to the development of human society. Specifically, a considerable amount of low-grade heat (LGH), typically below 100 °C, is currently being wasted. However, efficient utilization of this LGH can relieve energy shortages and reduce carbon dioxide emissions. To address this challenge, reverse electrodialysis heat engine (REDHE) which can efficiently convert LGH into electricity has emerged as a promising technology in recent years. Extensive efforts have been dedicated to exploring more suitable thermal distillation technologies for enhancing the performance of REDHE. This paper introduces a novel REDHE that incorporates helium-gap diffusion distillation (HGDD) as the thermal separation (TS) unit. The HGDD device is highly compact and efficient, operating at a normal atmospheric pressure, which aligns with the operational conditions of the reverse electrodialysis (RED) unit. A validated mathematical model is employed to analyze the impacts of various operating and structural parameters on the REDHE performance. The results indicate that maintaining a moderate molality of the cold stream, elevating the inlet temperatures of hot and cold streams, lengthening hot- and cold-stream channels, and minimizing the thickness of helium gaps contribute to improving the REDHE performance. Especially, a maximum energy conversion efficiency of 2.96% is achieved by the REDHE when decreasing the thickness of helium gaps to 3 mm and increasing the length of stream channels to 5 m.

关键词： helium-gap diffusion distillation (HGDD)     reverse electrodialysis (RED)     heat engine     low-grade heat (LGH)    

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Reaction kinetics and internal diffusion of Zhundong char gasification with CO

Yun Liu, Jiangyuan Qu, Xuehui Wu, Kai Zhang, Yuan Zhang

《化学科学与工程前沿（英文）》 2021年 第15卷 第2期   页码 373-383 doi: 10.1007/s11705-020-1949-2

摘要： Mass transfer usually affects the rate of chemical reactions in coal. The effect of internal diffusion on char gasification with CO in the temperature range from 1123 K to 1273 K was investigated via thermo-gravimetric analysis and assessment of char morphology features. The results revealed that the effect of internal diffusion on the initial reaction rate was more significant with an increase of particle size, due to the concentration gradient of the gasification agent within the solid particles. In the early stage of gasification, the generation of new micropores and the opening of closed pores led to an increase in specific surface area. As the reaction proceeded, the openings were gradually expanded and the specific surface area continued to increase. However, with further reaction, disappearance of edge pores, melting and collapse of the pore structure led to a decrease in specific surface area. The intrinsic activation energy and reaction order based on the th-order model were 157.67 kJ∙mol and 0.36, respectively. Thus, temperature zones corresponding to chemical reaction and diffusion control were identified. Moreover, the calculated effectiveness factor provided a quantitative estimation of internal diffusion in the initial stage.

关键词： coal char     CO2 gasification     internal diffusion     pore evolution    

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Intrinsic kinetics and external diffusion of catalytic steam gasification of fine coal char particles

Xuantao Wu, Jie Wang

《化学科学与工程前沿（英文）》 2019年 第13卷 第2期   页码 415-426 doi: 10.1007/s11705-018-1725-8

摘要： Catalytic steam gasification of fine coal char particles was carried out using a self-made laboratory reactor to determine the intrinsic kinetics and external diffusion under varying pressures (0.1–0.5 MPa) and superficial gas flow velocities (GFVs) of 13.8–68.8 cm?s . In order to estimate the gas release rate at a low GFV, the transported effect of effluent gas on the temporal gasification rate pattern was simulated by the Fluent computation and verified experimentally. The external mass transfer coefficients ( ) and the effectiveness factors were determined at lower GFVs, based on the intrinsic gasification rate obtained at a high GFV of 55.0 cm?s . The was found to be almost invariable in a wider carbon conversion of 0.2–0.7. The variations of at a median carbon conversion with GFV, temperature and pressure were found to follow a modified Chilton-Colburn correlation: (0.04< <0.19), where is total pressure and is atmospheric pressure. An intrinsic kinetics/external diffusion integrating model could well describe the gasification rate as a function of GFV, temperature and pressure over a whole gasification process.

关键词： coal char     catalytic steam gasification     pressure     kinetics     diffusion    

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Moisture diffusion behavior of permeable fiber-reinforced polymer composite

Jianjiang YANG, Qingsheng YANG, Lianhua MA, Wei LIU,

《机械工程前沿（英文）》 2010年 第5卷 第3期   页码 347-352 doi: 10.1007/s11465-010-0093-y

摘要： A unit cell approach is employed to predict the effective moisture diffusion property in fiber-reinforced biopolymer. The permeable fibers distributed in the matrix are taken as inclusion phases in the system. Based on a unit cell model, the calculation method for moisture diffusion coefficients is developed in this paper. Moisture diffusion property and effective diffusion coefficients are numerically investigated under different temperature and volume fractions of fibers. The calculated results agree well with Gueribiz’s solutions. Therefore, it is reliable in predicting moisture diffusion property of composite using the unit cell model. The present result shows that the effective diffusion coefficient of a composite depends on both temperature and volume fraction of fibers. The effective diffusion coefficient of regular hexagon pattern composite is larger than that of square pattern at the same temperature and volume fraction.

关键词： fiber-reinforced biopolymer     effective diffusion coefficient     unit cell     finite element modeling (FEM)    

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标题 作者 时间 类型 操作

A comprehensive assessment on the durability of gas diffusion electrode materials in PEM fuel cell stack

Arunkumar JAYAKUMAR

期刊论文

Molecular diffusion in ternary poly(vinyl alcohol) solutions

期刊论文

evaluation of renal function using diffusion weighted imaging and diffusion tensor imaging in type 2

null

期刊论文

Coupled diffusion of chloride and other ions in saturated concrete

Nattapong DAMRONGWIRIYANUPAP, Linyuan LI, Yunping XI

期刊论文

Magnetohydrodynamic slip flow and diffusion of a reactive solute past a permeable flat plate with suction

Krishnendu BHATTACHARYYA, G. C. LAYEK

期刊论文

Chloride diffusion in concrete with carbonated recycled coarse aggregates under biaxial compression

期刊论文

Experimental study of humid air reverse diffusion combustion in a turbulent flow field

GE Bing, ZANG Shusheng, GU Xin

期刊论文

Fuel variability effect on flickering frequency of diffusion flames

Jizhao LI, Yang ZHANG

期刊论文

Transient process of methane-oxygen diffusion flame-street establishment in a microchannel

期刊论文

Preparation of a Pb loaded gas diffusion electrode and its application to CO

Ang LI, Hua WANG, Jinyu HAN, Li LIU

期刊论文

Determination of the diffusion of poly(ethylene glycol) in polypropylene using ATR-FTIR

Hanjia CHEN, Xuhua SHI, Yafei ZHU, Yi ZHANG, Jiarui XU,

期刊论文

Reverse electrodialysis heat engine with helium-gap diffusion distillation: Energy efficiency analysis

期刊论文

Reaction kinetics and internal diffusion of Zhundong char gasification with CO

Yun Liu, Jiangyuan Qu, Xuehui Wu, Kai Zhang, Yuan Zhang

期刊论文

Intrinsic kinetics and external diffusion of catalytic steam gasification of fine coal char particles

Xuantao Wu, Jie Wang

期刊论文

Moisture diffusion behavior of permeable fiber-reinforced polymer composite

Jianjiang YANG, Qingsheng YANG, Lianhua MA, Wei LIU,

期刊论文