Optimizing Weights of Platinum in the Active Layer of the Cathode of a Hydrogen–Oxygen Fuel Cell with a Solid Polymer Electrolyte

The active layer of the cathode of a hydrogen–oxygen fuel cell with a solid polymer electrolyte is computer simulated. The active mass of the electrode consists of substrate grains (agglomerates of carbon particles with Pt particles embedded into them) and grains of a solid polymer electrolyte (Nafion). The substrate grains presumably contain hydrophobic pores, which facilitate the oxygen penetration into the active mass. A calculation of characteristics of such an electrode focuses on the optimization of platinum weights. The principal parameters of the system are concentration and size of grains of substrate and Nafion, Pt concentration in substrate grains, average diameter of hydrophobic pores in substrate grains, and the electrode polarization. The optimum, at a given electrode polarization, electrochemical activity of the active layer, its thickness, and the platinum weight are calculated. A link between these quantities and principal parameters of the active layer is revealed.     

Optimization of Mass Transfer Processes in the Zone of the Air Electrode of a Fuel Cell with a Solid Polymer Electrolyte

A two-dimensional mathematical model for the transport of reactants in a fuel cell with a solid polymer electrolyte is developed. The model is used for analyzing spatial distributions of the concentration of reactants and current density over the cell. The effect of the catalytic-layer activity, reactant speed, bipolar-plate geometry, thickness and porosity of current collector and/or gas-diffusion sublayer, and the reaction mixture composition on the fuel cell efficiency is estimated theoretically and experimentally.     

碱性固体燃料电池碱性聚合物电解质膜的最新研究进展

最近,碱性聚合物电解质膜燃料电池（APEMFC）因具有电极反应动力学快以及不依赖于贵金属铂催化剂等诸多优点而成为一个热门话题. 作为其中一个关键部件,碱性聚合物电解质膜直接影响燃料电池的性能和成本.然而,迄今为止,仍然没有令人满意的碱性电解质膜材料. 为此,大量研究被开展和报道. 本文综述了近三年内文献中关于燃料电池碱性聚合物电解质膜的最新研究进展：包括各种各样的合成策略,构效关系,水管理以及非原位或原位稳定性测试等等. 尤其是一些新的金属离子基阴离子交换膜和冠醚基阴离子交换膜首次被提及和评论.此外,还进一步预测了将来的发展趋势.     

碱性固体燃料电池碱性聚合物电解质膜的最新研究进展

最近,碱性聚合物电解质膜燃料电池（APEMFC）因具有电极反应动力学快以及不依赖于贵金属铂催化剂等诸多优点而成为一个热门话题. 作为其中一个关键部件,碱性聚合物电解质膜直接影响燃料电池的性能和成本.然而,迄今为止,仍然没有令人满意的碱性电解质膜材料. 为此,大量研究被开展和报道. 本文综述了近三年内文献中关于燃料电池碱性聚合物电解质膜的最新研究进展：包括各种各样的合成策略,构效关系,水管理以及非原位或原位稳定性测试等等. 尤其是一些新的金属离子基阴离子交换膜和冠醚基阴离子交换膜首次被提及和评论.此外,还进一步预测了将来的发展趋势.     

Active layer of the cathode of a fuel cell with a solid polymer electrolyte: The effect of the Nafion concentration on the overall characteristics

A computer-aided simulation of the structure of the active layer of the cathode of a fuel cell with a solid polymer electrolyte (Nafion) is performed under the assumption about equidimensionalness of dimensions of grains of the substrate (with platinum crystallites in them) and grains (agglomerates of molecules) of Nafion. It is analyzed how the Nafion concentration affects principal parameters, which include the specific surface area, in the vicinity of which electrochemical process goes on; the effective ionic electroconductivity, and the effective diffusion coefficient of a gas. It is demonstrated how one can determine the Nafion concentration at which the overall current takes on a maximum value. Dependences of the optimum value of the overall current and the thickness of the active layer and the weight of platinum, which correspond to it, on the Nafion concentration are calculated. It is demonstrated that there in principle cannot exist one individual optimum concentration of Nafion, which is suitable for all techniques used for the preparation of the active layer. The mutual relationship between values of the effective diffusion coefficient of a gas and the effective ionic electroconductivity of Nafion determines the value of the optimum of the Nafion concentration.     

碱性固体燃料电池碱性聚合物电解质膜的最新研究进展

最近,碱性聚合物电解质膜燃料电池(APEMFC)因具有电极反应动力学快以及不依赖于贵金属铂催化剂等诸多优点而成为一个热门话题.作为其中一个关键部件,碱性聚合物电解质膜直接影响燃料电池的性能和成本.然而,迄今为止,仍然没有令人满意的碱性电解质膜材料.为此,大量研究被开展和报道.本文综述了近三年内文献中关于燃料电池碱性聚合物电解质膜的最新研究进展:包括各种各样的合成策略,构效关系,水管理以及非原位或原位稳定性测试等等.尤其是一些新的金属离子基阴离子交换膜和冠醚基阴离子交换膜首次被提及和评论.此外,还进一步预测了将来的发展趋势.     

Cathode of a hydrogen-oxygen fuel cell with a solid polymer electrolyte: The effect of the flooding of pores by water on the characteristics of the active layer

A computer model of the active layer of the cathode of a hydrogen-oxygen fuel cell with a solid polymer electrolyte is studied. The active mass of the electrode consists of equidimensional grains of the substrate (agglomerates of carbon particles with platinum particles embedded in them) and a solid polymer electrolyte (Nafion). The flooding by water can be experienced by both the pores in the substrate grains, which facilitate the oxygen penetration into the active layer of the electrode, and the voids between the grains. All possible versions of the flooding of these pores by water are considered. A calculation of the optimum, at a given polarization of the electrode, value of electrochemical activity, the thickness of the active layer, and the weight of platinum is performed. The major parameters of the system are the concentrations of grains of the substrate and solid polymer electrolyte, the size of these grains, the platinum concentration in the substrate grains, the average diameter of pores in the substrate grains, and the polarization of electrodes. The ultimate aim of the work is to estimate how the flooding of pores of the active layer of the cathode by water affects the magnitude of the optimum current, the effective thickness of the active layer, and the weight of platinum.Translated from Elektrokhimiya, Vol. 41, No. 1, 2005, pp. 35–47.Original Russian Text Copyright © 2005 by Chirkov, Rostokin.     

活性炭载体对聚合物电解质膜燃料电池中炭载铂电催化剂性能的影响

分别以松木炭和Vulcan XC-72炭为载体制得载铂电催化作用，在聚合物电解质膜燃料电池（PEMFC）中对其性能进行了比较。结果表明：Vulcan XC-72炭作载体的电催化剂性能显著优于松木炭作载体的电催化剂，利用多种分析对活性炭的物理和表面化学性质进行了系统的研究，发现活性炭的孔径、电导率和表面含氧基团和电催化剂性能有很大的影响。     

Cathode of a fuel cell with a solid polymer electrolyte: Calculating overall currents in the presence of a gas-diffusion layer

Mathematical apparatus, which makes it possible to perform calculations of the current-voltage characteristics of cathodes of fuel cells with a solid polymer electrolyte in conditions where there are present extraneous diffusion restrictions is proposed. In so doing, the partial pressure of oxygen and the absolute pressure of gas in the gas chamber may assume any values. First of all presented are the results of calculations of the current-voltage characteristics intrinsic to active layers of the air and oxygen cathodes, which are performed under the assumption that the extraneous diffusion restrictions are absent altogether. Thereafter, in the same conditions (at the same parameters that characterize the active layer of a cathode), obtained are results of a calculation of the current-voltage characteristics inherent in the air and oxygen cathodes in the presence of extraneous diffusion restrictions. Afterward there is performed an analysis of the way a gas-diffusion layer restricts the process of generation of current in a cathode and of what measures should be taken in order for the extraneous diffusion restrictions to become less significant.     

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.     

Mass transfer in porous systems, flooded in part with water, of gas diffusion and catalytic layers of the cathode of a fuel cell with a solid polymer electrolyte

Mass transfer in porous gas diffusion and catalytic layers of the cathode of a hydrogen-air fuel cell with a solid polymer electrolyte is considered. The transport processes are considered with allowance made for the partial flooding of porous systems of these layers with water, which forms during the fuel cell operation. The consideration also allows for the influence of the diluent gas present when air oxygen is used as the oxidant. The fraction of water-flooded pores is calculated within percolation theory as a function of structural parameters of the porous system. Conditions leading to the beginning of the gas diffusion layer flooding are presented.     

Active layer of the oxygen cathode in a fuel cell with Nafion and platinum: The role played by the diffusion and ohmic restrictions and the selection of the working thickness of the active layer

The basic parameters that characterize the operation of the active layer of a cathode with Nafion are the effective coefficient of the diffusion of oxygen, the effective ionic conductance, and the thickness of the active layer. One of the deficiencies intrinsic to the fuel cells containing Nafion is their extreme sensitivity to the heat and moisture exchange. Nafion demands an optimum degree of humidification. Upon thoroughly draining the active layer of a cathode with Nafion, its effective ionic conductance substantially lowers, and large diffusion restrictions arise following the flooding of pores in the active layer. The goal of this work is to perform a comparison of values of some dimensional characteristics pertaining to the flooded and thoroughly drained active layers of a cathode with similar indicators of an active layer in its optimum (normal) state. It is demonstrated how one should perform the selection of the working thickness of an active layer that would provide for the efficiency of its functioning.     

Calculation of optimum thickness of active layer of oxygen and air cathodes of fuel cell with Nafion and platinum

It is shown that, for the electrodes of fuel cells with solid polymer electrolyte, the dependence of overall current on the active layer thickness contains an extremum. There is an optimum thickness of active layer, at which the overall current reaches its maximum possible value. The nature of this dependence is explained. The character of the distribution of electrochemical process intensity over the depth of active layer of cathode with solid polymer electrolyte is analyzed. The optimum thicknesses of active layers of oxygen and air cathodes of fuel cells with Nafion and platinum and the corresponding overall currents and contents of catalyst in the active layer are calculated. In the calculations, the temperature of fuel cell, the pressure in the cathode gas chamber, and the cathodic potential were varied. The optimization of active layer thickness of cathode with solid polymer electrolyte can reduce the platinum consumption, i.e. its amount per 1 kW of power produced in a membrane-electrode assembly.     

基于电-化-热耦合理论对称双阴极固体氧化物燃料电池堆的电流与温度场数值模拟

本文基于电-化-热多场耦合理论,通过有限元方法建立了一个基于对称双阴极结构SOFC电堆单元的三维数值模型,研究了其电堆内部的电流密度分布和温度分布. 研究结果表明,气体流动方式以及集流方式影响了电解质上电流密度和温度分布：在气体进、出气口处有较大的电流密度分布;在气体共流模式下,电解质层温度分布却较均匀;在双阴极结构电池阴极侧的单一集流模式下,集流侧的电解质的平均电流密度高于另一侧.     

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.