共查询到20条相似文献,搜索用时 46 毫秒
1.
Recent experimental results show that performance of a proton exchange membrane (PEM) fuel cell is improved when small particles of permanent magnet are deposited in the catalyst layer on the cathode side. In this study, the mechanism of this phenomenon was clarified by using numerical simulation. Permanent magnet particles induce a Kelvin (magnetic) repulsive force against liquid water and an attractive force towards oxygen gas. To precisely study the behavior of oxygen and liquid water flows near the interface between the catalyst layer and gas diffuser, the simulation domain included the catalyst layer and gas diffuser. The simulation results revealed the following. The Kelvin repulsive force against liquid water mainly “manages” the liquid water flow and improves the performance of the fuel cell, especially in the current-limited region. In the presence of Kelvin forces, the liquid water saturation near the interface between the catalyst layer and gas diffuser decreases, thus making more pore space available for transport of oxygen gas. Furthermore, the water velocity moving from the interface increases in the upstream region. The gas velocity near the interface also increases, and thus more oxygen is supplied to the reaction sites. In summary, the Kelvin force promotes removal of liquid water from the catalyst layer, thus providing more oxygen to the catalyst and improving the performance of the fuel cell. 相似文献
2.
Jay Benziger Erin Kimball Raquel Mejia‐Ariza Ioannis Kevrekidis 《American Institute of Chemical Engineers》2011,57(9):2505-2517
Oxygen transport across the cathode gas diffusion layer (GDL) in polymer electrolyte membrane (PEM) fuel cells was examined by varying the O2/N2 ratio and by varying the area of the GDL extending laterally from the gas flow channel under the bipolar plate (under the land). As the cathode is depleted of oxygen, the current density becomes limited by oxygen transport across the GDL. Oxygen depletion from O2/N2 mixtures limits catalyst utilization, especially under the land.The local current density with air fed PEM fuel cells falls to practically zero at lateral distances under the land more than 3 times the GDL thickness; on the other hand, catalyst utilization was not limited when the fuel cell cathode was fed with 100% oxygen. The ratio of GDL thickness to the extent of the land is thus critical to the effective utilization of the catalyst in an air fed PEM fuel cell. © 2010 American Institute of Chemical Engineers AIChE J, 2011 相似文献
3.
The effects of hydrophobicity of the cathode catalyst layer on the performance of a PEM fuel cell are studied. The surface contact angle is measured to understand the changes of the hydrophobicity of the cathode catalyst layer upon the addition of hydrophobic dimethyl silicone oil (DSO). The results show that the contact angle increases with the DSO loadings in the cathode catalyst layer ranging from 0 to 0.65 mg/cm2. The subsequent electrochemical measurements of the fuel cells with various cathodes reveal that the addition of DSO in the cathode catalyst layer can effectively prevent the cathode flooding at high current density, thus leading to a much higher limiting current density and the maximum power density when compared to the fuel cell with a normal cathode. An optimal DSO loading in the cathode catalyst layer is found to be around 0.5 mg/cm2 under the testing conditions in this work. The fuel cell with cathode loaded with 0.5 mg/cm2 can reach the maximum power density of 356 mW/cm2 in H2/air (or 709 mW/cm2 in H2/O2) at room temperature, which is around 2.5 times in H2/air (or 1.8 times in H2/O2) of that with normal cathode. All of the results indicate that the hydrophobicity of the cathode catalyst layer plays a crucial role in the water management of the fuel cell. The possible function of the DSO on improved oxygen solubility for the oxygen starved cathode during flooding warrants some further investigation. 相似文献
4.
J.J. Hwang C.K. Chen R.F. Savinell C.C. Liu J. Wainright 《Journal of Applied Electrochemistry》2004,34(2):217-224
A three-dimensional numerical model is developed to simulate the transport phenomena on the cathodic side of a polymer electrolyte membrane fuel cell (PEMFC) that is in contact with parallel and interdigitated gas distributors. The computational domain consists of a flow channel together with a gas diffusion layer on the cathode of a PEMFC. The effective diffusivities according to the Bruggman correlation and Darcy's law for porous media are used for the gas diffusion layer. In addition, the Tafel equation is used to describe the oxygen reduction reaction (ORR) on the catalyst layer surface. Three-dimensional transport equations for the channel flow and the gas diffusion layer are solved numerically using a finite-volume-based numerical technique. The nature of the multi-dimensional transport in the cathode side of a PEMFC is illustrated by the fluid flow, mass fraction and current density distribution. The interdigitated gas distributor gives a higher average current density on the catalyst layer surface than that with the parallel gas distributor under the same mass flow rate and cathode overpotential. Moreover, the limiting current density increased by 40% by using the interdigitated flow field design instead of the parallel one. 相似文献
5.
Fuqiang Liu 《Electrochimica acta》2006,52(3):1409-1416
The cathode catalyst layer in direct methanol fuel cells (DMFCs) features a large thickness and mass transport loss due to higher Pt loading, and therefore must be carefully designed to increase the performance. In this work, the effects of Nafion loading, porosity distribution, and macro-pores on electrochemical characteristics of a DMFC cathode CL have been studied with a macro-homogeneous model, to theoretically interpret the related experimental results. Transport properties in the cathode catalyst layers are correlated to both the composition and microstructure. The optimized ionomer weight fraction (22%) is found to be much smaller than that in H2 polymer electrolyte fuel cells, as a result of an optimum balance of proton transport and oxygen diffusion. Different porosity distributions in the cathode CLs are investigated and a stepwise distribution is found to give the best performance and oxygen concentration profile. Influence of pore defects in the CLs is discussed and the location of macro-pores is found to play a dual role in affecting both oxygen transport and proton conduction, hence the performance. The reaction zone is extended toward the membrane side and the proton conduction is facilitated when the macro-pores are near the gas diffusion layer. 相似文献
6.
常规流场下各向异性扩散层对质子交换膜燃料电池(PEMFC)性能影响 总被引:1,自引:0,他引:1
为了研究扩散层各向异性对电池性能的影响,以XD=Di,j ^y/Di,j ^x 为各向异性的表征,建立了使用常规流场的质子交换膜燃料电池二维传质模型.考虑了阴阳极内物质的对流和扩散、水和质子在膜内传递以及催化层的电化学反应.利用有限差分法对控制方程进行离散,采用逐次超松驰法求解得到了阴阳极反应气体和水的浓度分布以及催化层电流密度、膜中水含量、膜中电势和电流密度的分布.分析结果表明:在1≤XD≤4时增大XD有利于提高电池性能,但随着XD增大其对电池性能的影响逐渐减小;并且XD对电池性能的影响主要体现在对阴极和膜性能的影响上,其对阳极性能的影响甚微. 相似文献
7.
C. Christenn G. Steinhilber M. Schulze K. A. Friedrich 《Journal of Applied Electrochemistry》2007,37(12):1463-1474
The cathode catalysts in low temperature fuel cells are associated with major cell efficiency losses, because of kinetic limitations
of the oxygen reduction reaction. Additionally, methanol oxidation at the cathode leads to significant lowering of the efficiency
in direct methanol fuel cells, which can be alleviated by use of methanol-tolerant catalysts. In this work, alternative carbon-supported
platinum-alloy catalysts were investigated by physical methods. Second, methanol-tolerant ruthenium-selenide catalysts were
characterized by physical and electrochemical methods. Besides V–i characteristics and electrochemical impedance spectroscopy as electrochemical methods, physical methods such as X-ray photoelectron
spectroscopy, nitrogen adsorption, porosimetry by mercury intrusion and temperature programmed reduction are used to characterize
the catalysts. The electrochemical characterization yields information about properties and behavior of the catalyst. In contrast
to platinum a significantly different hydrophobic behavior of the RuSe/C catalysts is found. Low open circuit voltage values
measured for RuSe/C indicate an effect on both electrodes. The anode reaction was also influenced by the different cathode
catalysts. As a result of the formation of H2O2 at the cathode, which passes through the membrane from cathode to anode side, a mixed anode potential is formed. By comparing
RuSe/C catalysts before and after electrochemical stressing, changes of the catalysts are determined. Postmortem surface analysis
(by X-ray photoelectron spectroscopy) revealed that catalyst composition and MEA structure changed during electrochemical
stressing. During fuel cell operation selenium oxide is removed from the surface of the catalysts to a large extent. Additionally,
a segregation effect of selenium in RuSe to the surface is identified. 相似文献
8.
The performance of a proton exchange membrane fuel cell (PEMFC) with gas diffusion cathodes having the catalyst layer applied directly onto Nafion membranes is investigated with the aim at characterizing the effects of the Nafion content, the catalyst loading in the electrode and also of the membrane thickness and gases pressures. At high current densities the best fuel cell performance was found for the electrode with 0.35 mg Nafion cm−2 (15 wt.%), while at low current densities the cell performance is better for higher Nafion contents. It is also observed that a decrease of the usual Pt loading in the catalyst layer from 0.4 to ca. 0.1 mg Pt cm−2 is possible, without introducing serious problems to the fuel cell performance. A decrease of the membrane thickness favors the fuel cell performance at all ranges of current densities. When pure oxygen is supplied to the cathode and for the thinner membranes there is a positive effect of the increase of the O2 pressure, which raises the fuel cell current densities to very high values (>4.0A cm−2, for Nafion 112—50 μm). This trend is not apparent for thicker membranes, for which there is a negligible effect of pressure at high current densities. For H2/air PEMFCs, the positive effect of pressure is seen even for thick membranes. 相似文献
9.
Two steady-state, one-dimensional models of the cathode active layer for the proton exchange membrane fuel cell, a conventional active layer model with the agglomerate structure and an ordered active layer model, have been compared. The model equations account for the Tafel kinetics of oxygen reduction reaction, proton migration and oxygen diffusion in the polymer electrolyte and gas pores. The polarization curves simulated by the ordered active layer predict a superior performance than the conventional active layer model even with lower platinum loadings. Analysis of the overpotential contributions indicates that the better performance of the ordered catalyst layer can be attributed to the reduction of concentration polarization. Simulation results also reveal that the ordered active layer gives more uniform oxygen concentration and overpotential distributions while the conventional catalyst layer shows more evenly distributed local current source. The present results will be helpful for practical fuel cell designs. 相似文献
10.
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12.
液相进样直接甲醇燃料电池性能研究 总被引:6,自引:0,他引:6
报道了用研制的Pt-Ru/C催化剂, 采用特殊工艺制备了膜电极, 并组装了直接甲醇质子交换膜单电池系统。考察了电极扩散层制备方法、催化剂层中催化剂、Teflon-C以及Nafion液的用量等电极制备工艺条件以及空气作为氧化剂对单电池性能的影响。结果表明:采用刷涂法制备电极扩散层比喷涂法好,催化剂层中催化剂的优化含量为0.6mg·cm-2,Teflon-C、Nafion液的最佳用量分别为0.3 mg·cm-2、0.5 mg·cm-2。当工作温度为80℃时,输出电压为0.3V,氧气作为阴极气体的输出电流密度为36mA·cm-2;而空气作为阴极气体的输出电流密度为22.5mA·cm-2。膜电极有效面积为9cm2的的液相进样直接甲醇/氧气燃料电池三电池电堆的最大功率为0.285W,此时输出电压为0.7V,输出电流为0.407A;而液相进样直接甲醇/空气三电池电堆的输出电压为0.635V,输出电流为0.252A时,最大功率为0.160W。 相似文献
13.
A porous non‐platinum electrocatalyst for the oxygen reduction reaction (ORR), obtained by pyrolysing a cobalt porphyrin precursor, was evaluated by electrochemical means. The reactivity of the non‐platinum ORR catalyst was investigated with a rotating disc electrode (RDE) experimental set up. RDE data were collected in an acidic electrolyte containing N2, O2, CO and under mixed reactant O2/methanol conditions. The electrochemical performance of such‐obtained non‐platinum catalyst is discussed and compared to platinum‐based ORR catalysts. Based on the results collected here, we are able to propose and test possible proton exchange fuel cell (PEFC) operating conditions where non‐platinum ORR catalysts can be utilised. Direct methanol fuel cell (DMFC) data demonstrating a superior performance of the non‐platinum catalyst relative to platinum black, often perceived as the state‐of‐the‐art oxygen–reduction catalyst for the DMFC cathode is presented. 相似文献
14.
质子交换膜燃料电池阴极催化剂的位置效应 总被引:5,自引:3,他引:2
考虑局部几何效应,通过二维稳态数学模型研究了质子交换膜燃料电池阴极催化剂的位置与其表面传质和反应能力的关系。模型方程涉及氧气在催化层气孔的传输,氧气在气相和电解质相界面的分配以及氧气和质子在电解质中的传递和电化学反应过程。计算结果表明,催化剂表面的氧气扩散能力对催化剂的位置变化非常敏感,随催化剂深入电解质内部,其表面的氧气扩散能力经短暂上升后迅速下降。催化剂位置对质子传递阻力的影响与氧气扩散类似,但位置效应要弱些。性能比较确定最优的催化剂位置是恰好处于刚被电解质膜完全覆盖的位置。 相似文献
15.
Sehkyu Park 《Fuel》2009,88(11):2068-5582
The effect of the content of the hydrophobic agent in the cathode gas diffusion layer (GDL) on the mass transport in the proton exchange membrane fuel cells (PEMFCs) was studied using mercury porosimetry, scanning electron microscopy, and electrochemical polarization techniques. The mercury intrusion data and SEM micrograph indicated that the hydrophobic agent alters the surface and bulk structure of the GDL, thereby controlling gas-phase void volume and liquid water transport. The electrochemical polarization curves were measured and quantitatively analyzed to determine the oxygen transport limitation both in the catalyst layer and the GDL. Evaluation of the parameter ζ, which represents the cathode GDL characteristics for liquid water transport, indicated that the optimized content of the hydrophobic agent and effective water management results from a trade-off between the hydrophobicity and the absolute permeability for faster water drainage. 相似文献
16.
Dieter von Deak Elizabeth J. Biddinger Umit S. Ozkan 《Journal of Applied Electrochemistry》2011,41(7):757-763
Accelerated electrochemical corrosion of nitrogen-containing carbon (CN
x
) oxygen reduction catalysts was performed by a chronoamperometric hold at 1.2 V versus NHE in acidic electrolyte using a
rotating disk electrode system. Cyclic voltammograms were used to measure the electrochemically active quinone/hydroquinone
redox reaction couple indicating the degree of carbon corrosion. Half-cell testing of CN
x
oxygen reduction catalyst materials showed superior carbon corrosion resistance compared to Vulcan carbon, the most ubiquitous
cathode catalyst support. When oxygen reduction activity was measured before and after carbon corrosion, carbon corrosion
resilience trended with the oxygen reduction activity. CN
x
catalysts subjected to carbon corrosion testing did not show a change in the onset of oxygen reduction reaction (ORR) activity
potentials with only a slight reduction in current density, but showed improved ORR selectivity to the complete reduction
of dioxygen to water. 相似文献
17.
S. Ho?evar E. Passalacqua M. Vivaldi A. Patti N. Giordano 《Electrochimica acta》1996,41(18):2817-2827
The optimization procedure of gas diffusion electrode (anode and cathode) development is described for a new type of low temperature fuel cell using as proton conducting electrolyte a concentrated aqueous solution of H3PW12O40 acid. The procedure consists of full factorial design of experiments performed by varying three variables:
- 1. (a) content of polytetrafluoroethylene (PTFE) in the catalyst layer of electrodes;
- 2. (b) content of fluoroethylenepropylene (FEP) in the diffusional (supporting) layer of electrodes; and
- 3. (c) thickness of the diffusional layer of electrodes on three levels (low, medium and high) during the measurements of hydrogen permeability through dry electrodes, measurements of electrolyte absorption in the electrodes and during the electrochemical measurements of polarization curves for oxygen reduction, hydrogen oxidation and of the oxygen gain in a half-cell at room temperature.
18.
《Ceramics International》2020,46(12):20335-20344
Binary Mn/Co oxide sheets with spherical flower-like hierarchical structure are grown directly on the surface of a Ni foam skeleton as a cathode for Li–O2 batteries using a hydrothermal method. This integrated cathode architecture eliminates the negative effects of a conductive carbon additive and binder on the electrochemical performance of Li–O2 batteries and minimizes the processing steps in fabrication of cathodes for Li–O2 batteries. The porous Ni foam acts as a scaffold and current collector, and the highly hierarchical porous flower-like structure of the binary Mn/Co oxide sheet acts as a highly active catalyst. Together, they facilitate effective diffusion of oxygen gas as well as rapid ion and electron conduction during electrochemical reactions. When assembled in Li–O2 cells, the prepared catalyst exhibits excellent catalytic activities, including the oxygen reduction and oxygen evolution reactions. In particular, the Li–O2 cell using the cathode delivers an extremely high specific discharge capacity of 9690 mAh g-1 under a applied specific current of 200 mA g-1 and operate successfully in a long lifespan of 66 cycles even under a high specific current of 600 mA g-1 and a limited discharge-charge capacity mode of 1000 mAh g-1. The simultaneous effect of the fast electron transport kinetics provided by the free-standing structure and the high catalytic activity of the binary Mn/Co oxide show promise for use in air electrodes for Li–O2 batteries. 相似文献
19.
J.-F. Drillet A. EeJ. Friedemann R. Kötz B. SchnyderV.M. Schmidt 《Electrochimica acta》2002,47(12):1983-1988
The electrochemical oxygen reduction reaction (ORR) was studied at Pt and Pt alloyed with 30 atom% Ni in 1 M H2SO4 and in 1 M H2SO4/0.5 M CH3OH by means of rotating disc electrode. In pure sulphuric acid, the overpotential of ORR at 1 mA cm−2 is about 80 mV lower at Pt70Ni30 than at pure Pt. It was found that in methanol containing electrolyte solution the onset potential for oxygen reduction at PtNi is shifted to more positive potentials and the alloy catalyst has an 11 times higher limiting current density for oxygen reduction than Pt. Thus, PtNi as cathode catalyst should have a higher methanol tolerance for fuel cell applications. On the other hand, no significant differences in the methanol oxidation on both electrodes was found using cycling voltammetry, especially regarding the onset potential for methanol oxidation. During all the measurements no significant electrochemical activity loss was observed at Pt0.7Ni0.3. Ex-situ XPS investigations before and after the electrochemical experiments have revealed Pt enrichment in the first surface layers of the PtNi. 相似文献
20.
Ahmad Nozad Golikand Elaheh Lohrasbi Mohammad Ghannadi Maragheh Mehdi Asgari 《Journal of Applied Electrochemistry》2009,39(12):2421-2431
This work tries to study the problem of methanol crossover through the polymer electrolyte in direct methanol fuel cells (DMFCs)
by developing new cathode electrocatalysts. For this purpose, a series of gas diffusion electrodes (GDEs) were prepared by
using single-walled carbon nanotubes (SWCNTs) supported Pt–Pd (Pt–Pd/SWCNT) with different Pd contents at the fixed metal
loading of 50 wt%, as bimetallic electrocatalysts, in the catalyst layer. Pt–Pd/SWCNT was prepared by depositing the Pt and
Pd nanoparticles on a SWCNTs support. The elemental compositions of bimetallic catalysts were characterized by inductively
coupled plasma atomic emission spectroscopy (ICP-AES) system. The performances of the GDEs in the methanol oxidation reaction
(MOR) and in the oxygen reduction reaction with/without the effect of methanol oxidation reaction were investigated by means
of electrochemical techniques: cyclic voltammetry (CV), linear sweep voltammetry (LSV), and electrochemical impedance spectroscopy
(EIS). The results indicated that GDEs with Pt–Pd/SWCNT possess excellent electrocatalytic properties for oxygen reduction
reaction in the presence of methanol, which can originate from the presence of Pd atoms and from the composition effect. 相似文献