Performance of catalyst layers of polymer electrolyte fuel cells: exact solutions

Performance of a catalyst layer of polymer electrolyte fuel cell under the assumptions of ideal transport of reactants and Tafel kinetics of electrochemical reaction is considered. Explicit expressions for the profiles of basic parameters (proton current density, overpotential and reaction rate) across the catalyst layer are obtained and a new conservation law is found. Exact expression for voltage–current curve of the catalyst layer is derived and simplified in the limiting cases of small and large current densities. The physics of transition from small to large currents is discussed.     

Model for the multicomponent gas diffusion in a fuel cell porous electrode

A simple analytically solvable model for the diffusion of a multicomponent vapor-air mixture is proposed. The model, which accurately accounts for the oxygen and water balance on the gas diffusion cathode of a fuel cell, is used for computing polarization characteristics of a fuel cell with a polymer electrolyte. An analytical solution for the cathodic overvoltage in the extreme cases of high and low current densities is derived. The results are compared with the available theoretical and experimental data. It is shown that the solutions of the proposed model coincide with the solutions provided by the Bernardi-Verbrugge model, which is far more involved.     

The voltage–current curve of a direct methanol fuel cell: “exact” and fitting equations

Based on exact solutions of the problem of catalyst layer performance, the fitting equation for voltage–current curve of a direct methanol fuel cell is derived. Voltage losses due to imperfect transport of reactants in the diffusion layers and due to methanol crossover are taken into account. The coefficients in fitting equation are expressed in terms of basic transport and kinetic parameters on both sides of the cell. Fitting of experimental voltage–current gives the estimate of these parameters. The formula for optimal methanol concentration is derived; with good accuracy it reproduces the experimental value.     

A novel electrode architecture for passive direct methanol fuel cells

The supply of cathode reactants in a passive direct methanol fuel cell (DMFC) relies on naturally breathing oxygen from ambient air. The successful operation of this type of passive fuel cell requires the overall mass transfer resistance of oxygen through the layered fuel cell structure to be minimized such that the voltage loss due to the oxygen concentration polarization can be reduced. In this work, we propose a new membrane electrode assembly (MEA), in which the conventional cathode gas diffusion layer (GDL) is eliminated while utilizing a porous metal structure for transporting oxygen and collecting current. We show theoretically that the new MEA enables a higher mass transfer rate of oxygen and thus better performance. The measured polarization and constant-current discharging behavior showed that the passive DMFC with the new MEA yielded better and much more stable performance than did the cell having the conventional MEA. The EIS spectrum analysis further demonstrated that the improved performance with the new MEA was attributed to the enhanced transport of oxygen as a result of the reduced mass transfer resistance in the fuel cell system.     

Physico-Mathematical Model of the Gas Flow in the Channel between the Separator Plate and the Anode of a Fuel Cell with Molten Carbonate Electrolyte

Some models for the gas mixture composition variation in the channel between the separator plate and anode of a molten carbonate fuel cell are considered. A two-dimensional model for the carbon dioxide diffusion in the channel is solved analytically and numerically. The anodic current density is estimated.     

A new method of preparing a rotating ring-disc electrode for the study of carbon supported catalysts

A new preparation method is described for the study of carbon supported electrodes, which are currently under investigation for fuel cell applications. The carbon is applied to the disc of a rotating ring—disc electrode (RRDE) through incorporation of the carbon particles ina polypyrrole film. Electron transport to the carbon is possible because the polypyrrole is electronically conducting; the high porosity of the film enables the diffusion of reactants into the pores of the catalyst. This new technique offers an easy and quick way of measuring both the activity and selectivity of carbonsupported catalysts.     

Performance of a polymer electrolyte fuel cell with long oxygen channel

Along-the-channel analytical model of a polymer electrolyte fuel cell is developed. The model takes into account oxygen diffusion in backing layer, diffusion and electroosmotic transport of water in membrane and oxygen depletion in a feed channel. Voltage current curve of a cell, which takes into account all these processes is obtained and expression for limiting current density is derived. The latter shows, that cell performance is described by design parameters, which are combinations of geometrical and working parameters. The region of optimal cell performance on the plane of the design parameters is determined.     

Intensification of proton conductivity through polymer electrolytic membrane using novel electrode pattern

The performance of a polymer electrolyte membrane fuel cell is contingent on the focal property of the protonic conductivity to accelerate the electrochemical reaction based on the membrane activity or on the uniform and even distribution of the reactants. For the even distribution, novel Flow Fields (FF) of the electrode pattern are obligatory to maintain the distribution for a long period for the conversion of protons from the anode reactant. In this study, a novel X Flow Field (XFF) electrode pattern is developed and compared with the conventional serpentine Flow Field (SFF) electrode pattern numerically and experimentally. The performance of the cell through the XFF electrode pattern has shown an improvement of 14.89% numerically and 14.61% experimentally as it distributes the reactants evenly to accelerate the electrochemical reaction, and induce a lower pressure drop and lower water saturation. The effect of pressure and Mass Flow Rate (MFR) of the reactants on the cell performance is discussed and it is found that the increment in Power Density (PD) of the cell is proportional to the increment of the MFR and the pressure because of the even distribution of the reactants, better membrane protonic conductivity, enhancement of the electrode kinetics and improvement in the mass transfer.     

质子交换膜燃料电池及电池组模型分析

本文对现有质子交换膜燃料电池以及电池组模型进行比较分析,认为数学模型的建立,可以增加对燃料电池及电池组内部的传递现象和反应机理的认识,同时可以预测电池以及电池组的性能,并且对优化电池结构参数具有指导意义.模型分析包括了现阶段质子交换膜燃料电池单电池模型和电池组模型的基本类别,它们是单电池CFD数值模拟模型、单电池以及电池组性能模拟模型、燃料电池组气体分配模型、系统模型和非稳态模型.比较了几种模型的建模方式及不同模型的应用范围和各自的优缺点.     

Theoretical considerations on fuel cell electrodes design for in operando transmission X-ray absorption spectroscopy of the cell cathode

Conventional design of fuel cell electrodes for transmission X-ray absorption spectroscopy of the cell cathode includes Pt removal from a small anode spot. This spot serves as a transparent window for an X-ray beam probing the state of the cathode Pt atoms. A model shows that the current distribution over the surface of the cathode sample in front of the spot is strongly nonuniform, and hence, the sample does not necessarily represent the state of Pt atoms in a working fuel cell. The model suggests making the cathode sample in the form of a narrow ring, with Pt atoms being removed from the internal disk. Current density distribution over the ring surface is nearly homogeneous and close to the mean cell current density. The width of the ring should be in the order of the thickness of the membrane separating the anode and cathode.     

基于新球型微观结构模型模拟PEMFC催化层

建立了一个新球型催化层微观结构模型, 并基于此模型对质子交换膜燃料电池(PEMFC)性能进行了模拟. 该模型中假设催化层由Pt/C 颗粒和离子聚合物-孔混合相组成. 假设Pt/C 颗粒为球形结构, 其直径符合正态分布, 用不同直径的球来表示随机分散在电极中的Pt/C 颗粒. 计算了催化层内的传递和电化学反应, 研究了质子和氧气及电化学反应速率在电极厚度方向上的分布, 并且通过对比氧气浓度、过电位和电化学反应速率的分布、极化曲线及催化剂利用率等证明了适当的电极厚度与Pt/C颗粒粒径有利于提高电池性能.     

Analyzing leakage current in a direct methanol fuel cell

Journal of Solid State Electrochemistry - A mathematical model is developed to study the transient leakage current in a direct methanol fuel cell (DMFC) system. The DMFC is divided into five...     

Analytical model of the anode side of DMFC: the effect of non-Tafel kinetics on cell performance

Analytical model of the anode side of a direct methanol fuel cell is developed. The model takes into account non-Tafel kinetics of electrochemical reaction of methanol oxidation, diffusion transport of methanol through the backing layer and methanol crossover. General expression for the polarization voltage of the anode side is derived and simplified in a limits of small and large currents. Total limiting current density appears to be a combination of reaction- and diffusion-limiting current densities. The effect of methanol crossover on performance of the anode side is rationalized.     

Microfluidic devices for energy conversion: planar integration and performance of a passive, fully immersed H2-O2 fuel cell

We describe the fabrication and performance of a passive, microfluidics-based H2-O2 microfluidic fuel cell using thin film Pt electrodes embedded in a poly(dimethylsiloxane) (PDMS) device. The electrode array is fully immersed in a liquid electrolyte confined inside the microchannel network, which serves also as a thin gas-permeable membrane through which the reactants are fed to the electrodes. The cell operates at room temperature with a maximum power density of around 700 microW/cm(2), while its performance, as recorded by monitoring the corresponding polarization curves and the power density plots, is affected by the pH of the electrolyte, its concentration, the surface area of the Pt electrodes, and the thickness of the PDMS membrane. The best results were obtained in basic solutions using electrochemically roughened Pt electrodes, the roughness factor, R(f), of which was around 90 relative to a smooth Pt film. In addition, the operating lifetime of the fuel cell was found to be longer for the one using higher surface area electrodes.     

Fuel cell performance assessment for closed-loop renewable energy systems

Fuel cells and electrolysis are promising candidates for future energy production from renewable energy sources. Usually, polymer electrolyte fuel cell systems run on hydrogen and air, while the most of electrolysis systems vent out oxygen as unused by-product. Replacing air with pure oxygen, fuel cell electrochemical performance, durability and system efficiency can be significantly increased with a further overall system simplification and increased reliability. This work, which represents the initial step for pure H_2/O_2 polymer electrolyte fuel cell operation in closed-loop systems, focuses on performance validation of a single cell operating with pure H_2/O_2 under different relative humidity(RH) levels, reactants stoichiometry conditions and temperature. As a result of this study, the most convenient and appropriate operative conditions for a polymer electrolyte fuel cell stack integrated in a closed loop system were selected.     

聚苯胺修饰Pt/C催化剂对质子交换膜燃料电池动态响应的促进作用

将超级电容器材料聚苯胺引入电极催化剂中以缓冲燃料电池负载的变化.以硫酸为掺杂剂,将化学法合成的聚苯胺(PANI)与Pt/C超声分散混合,制成PANI-Pt/C催化剂.PANI-Pt/C的循环伏安测试和作为质子交换膜燃料电池阴极电催化剂的电池性能测试表明,PANI含量为10%时能够提高Pt/C催化剂对氧的还原动力学速度和燃料电池放电性能.电池在不同电流负载下的电压动态响应和对电池脉冲电流的动态响应以及PANI-Pt/C催化剂多电位电势阶跃计时电流测试显示,聚苯胺在催化剂中具有在瞬间电流负载时缓冲电池电压和电池大电流放电时平稳电压的作用.     

Hydrogen-oxygen (air) fuel cell with nafion and platinum: Calculating overall characteristics,comparing the performance of a cathode with polymeric electrolyte with a hydrophobized cathode with liquid electrolyte

Results of calculating the major overall characteristics of both an individual cathode and the whole hydrogen-oxygen (air) fuel cell with Nafion and platinum are shown. The effect of varying the parameters of both the active layer and the polymeric-electrolyte membrane on the overall characteristics of such a fuel cell is analyzed. The mechanisms of operation of active layers of hydrophobized cathodes and cathodes containing Nafion are compared. These two electrode types demonstrate a qualitative difference in the current generation mechanisms. As a result, the current in cathodes with Nafion increases more actively with the increase in over-potential (in proportion with exp [η₀/2], where η₀ is the cathodic overpotential) as compared with the case of hydrophobized cathodes (here the current ～ exp[η₀/4]). This explains the fact that a fuel cell with Nafion demonstrates so high power characteristics as compared with a fuel cell with hydrophobized electrodes and liquid electrolyte.     

Measurement of the current distribution along a single flow channel of a solid polymer fuel cell

We present a method of performing high spatial and time-resolution, non-intrusive and dynamic current measurements along the length of a single flow channel in a solid polymer fuel cell. Current profiles at different cell polarisations and reactant flow rates are examined along with the dynamic response of the fuel cell upon introduction of reactant gases.     

Heat transport in a PEFC: Exact solutions and a novel method for measuring thermal conductivities of the catalyst layers and membrane

We develop a model of heat transport in the membrane–electrode assembly of a polymer electrolyte fuel cell. The exact analytical solutions to model equations are derived. Rather cumbersome solutions lead to remarkably simple formulas for the temperature of the anode and the cathode sides of the membrane. Based on these formulas a novel method for measuring thermal conductivities of the catalyst layers and membrane in a working fuel cell environment is proposed.