固体氧化物燃料电池三维模拟与性能分析

建立了平板式阳极支撑固体氧化物燃料电池的三维数学模型,通过耦合电化学动力学和流体动力学模拟了电池的传热传质等传输现象。采用有限容积法计算了质量、动量、组分与能量守恒方程。研究给出了同向流与反向流情况下电流度密度、电压与功率密度分布。结果显示在同向流情况下,电池的最大功率密度较大,温度分布较均匀合理。进一步研究表明多孔电极结构参数（孔隙率、曲折因子与孔径尺寸）对电池性能有十分重要的影响。比较计算的极化性能与文献的实验数据,结果表明两者吻合的较好。     

基于伪二维电化学-热耦合模型的锂电池热特性研究

锂电池放电过程中的产热受电池内部电化学反应和欧姆效应影响,电池产热由电池化学与动力学决定,而电池动力学依赖于电池运行条件和设计参数。锂电池的六个温度依赖性参数对锂电池的放电过程中的产热速率具有影响,包括固相活性颗粒和电解液中的锂离子扩散系数、反应速率常数、电极开路电压、电解液离子电导率、热力学因子和阳离子迁移数。基于LiFePO_4圆柱形电池建立了伪二维电化学-热耦合模型,研究电池在恒流放电过程中的产热速率,以及正极、隔膜和负极各部分的产热速率和所占比例。结果表明,总产热功率随反应热的波动而变化,其中正极电极层中反应热占比最大,负极电极层中极化产热所占比例高于正极,而隔膜中的产热主要来源自欧姆热。不同对流传热系数条件下,电池的表面温度和内部温度差都不同,因此要合理的采取电池热管理措施。     

Principle and application of electrochemical impedance spectroscopy method

电化学阻抗测定技术是一种研究电极反应动力学和电化学体系中物质传递与电荷转移的有效方法,通过电化学阻抗数据所提供的信息,能够分析电极过程的特征,包括动力学极化,欧姆极化和浓差极化,为电化学过程设计,电极材料开发和电极结构研究提供基本依据.本文在介绍电化学阻抗谱技术原理的基础上,分别以液流电池,空气扩散电极过程为对象,阐述电化学阻抗谱中电荷转移,物质传递等过程以及多孔电极本身的电荷传递电阻等,并综述阻抗技术在设计电池结构,优化电极材料等方面的应用实例.     

质子交换膜燃料电池冷启动时阴极催化层内多场耦合的介孔尺度模型

为详细解析质子交换膜燃料电池（PEMFC）零下温度启动过程,建立了电池冷启动时多场耦合过程的介孔尺度数值模型。几何模型基于随机网格法（SGM）重建的催化层介孔结构,数学模型描述了物质传输、电荷传输、电化学反应和汽-冰相变过程。数值分析了电池冷启动过程中催化层内冰的生成和演化,重点探讨了冰的生成及形貌对电池性能的影响,推导出电化学活性反应面积与结冰量的关系式。     

钾离子电池锰基层状氧化物正极的研究进展北大核心CSCD

可再生能源替代传统化石燃料的研究推动了电能存储系统的发展。随着对规模储能的需求不断增加,钾离子电池(PIBs)因其成本低廉、元素丰度高、理论工作电压高以及电解液中K+卓越的传输动力学,在未来将成为商用锂离子电池的补充或替代品。电极材料的发展深刻影响电池的电化学性能。石墨作为钾离子电池负极展现出了优异的循环稳定性,然而,找到具有快速的传输动力学和稳定的框架结构来嵌入/脱嵌大尺寸K^(+)的正极材料是钾离子电池面临的主要挑战。层状过渡金属氧化物因其结构稳定、合成过程简单及价格低廉等优点而具有广阔的应用前景。本文介绍了钾含量和合成温度等对过渡金属层状氧化物晶体结构的影响,并说明了各种晶体结构在脱钾过程中的结构演变和容量损失机理;在此基础上,提出了针对不同晶体结构的锰基过渡金属层状氧化物的改性方法以提高其电化学性能;最后,对新型过渡金属层状氧化物正极的主要研究方向和研究热点进行了预测,以指导未来钾离子电池正极材料的发展。     

直接液体甲醇燃料电池流场组织行为研究(Ⅰ) 传统对称流道电池的模型建立

建立了直接甲醇燃料电池垂直流道方向电池单元的二维稳态数学模型,考虑了电化学动力学、多组分传递和甲醇渗透影响.计算了流道布置密度、扩散层、催化层和质子交换膜等组件尺度对电池内物料传质特性、化学反应组织和电池输出性能的影响.研究发现,增加流道布置密度、增加催化层厚度能有效提高电极反应均匀性和电池性能.其中催化层和质子膜的厚度影响最为显著,在该文研究范围内分别可提高电池的平均电流密度131.0%和17.8%.而扩散层和质子交换膜厚度都存在一个最佳值,需要与以上流场板设计尺寸和膜电极尺寸匹配.     

锂离子电池基础科学问题(ⅫⅠ)——电化学测量方法

电化学测量方法在锂离子电池研究中有着广泛的应用,常用于电极过程动力学基本信息的测量。本文首先简述了电化学测量的基本原理、电化学极化、测量方法特点等,并讨论了常见的测量方法在锂电池基础研究中的应用,包括循环伏安,电化学阻抗谱、恒电流间歇滴定、电位弛豫技术。     

Fundamental scientific aspects of lithium ion batteries(ⅫⅠ) —Electrochemical measurement

电化学测量方法在锂离子电池研究中有着广泛的应用,常用于电极过程动力学基本信息的测量。本文首先简述了电化学测量的基本原理、电化学极化、测量方法特点等,并讨论了常见的测量方法在锂电池基础研究中的应用,包括循环伏安,电化学阻抗谱、恒电流间歇滴定、电位弛豫技术。     

质子交换膜燃料电池数值分析

建立了一个三维的数学模型来模拟研究质子交换膜燃料电池,以及流道里流体的流动、阳极氢气和阴极氧气各组分的传递、热量传递、电荷传递、和氧化还原的电化学反应动力学,得到了电池内的组分浓度分布情况、温度场分布情况、以及多孔扩散层孔隙率对电池性能的影响.     

不同进气模式下平板式多孔介质电极SOFC的重整性能分析

在作者已开发的SOFC单电池结构及其阳极上甲烷重整的有效动力学模型的基础上,构建了直接内部重整的平板式多孔电极支撑(PES)固体氧化物燃料电池(SOFC)的全三维数学模型,根据模型分析了SOFC在不同进气模式顺流和逆流工况下,单电池内的流动、传热传质、化学、电化学和电流场等物理过程,给出了单电池内气体组分、温度、电势、电流密度等参数的空间分布。分析结果表明:进气方式对于电池的性能有一定的影响,与顺流相比在相同工况下燃用同样的燃料,采用逆流进气口电池的运行性能虽然略有提高,但是电池阳极内存在较高温度的热点,并且热点的位置不确定。     

质子交换膜燃料电池内部传热传质三维模拟

针对常规流场质子交换膜燃料电池提出了三维非等温数学模型。模型考虑了电化学反应动力学以及反应气体在流道和多孔介质内的流动和传递过程,详细研究了水在质子膜内的电渗和扩散作用。计算结果表明,反应气体传质的限制和质子膜内的水含量直接决定了电极局部电流密度的分布和电池输出性能;在电流密度大于0.3~0.4A/cm2时开始出现水从阳极到阴极侧的净迁移;高电流密度时膜厚度方向存在很大的温度梯度,这对膜内传递过程有较大影响。     

Numerical simulation of mass and charge transfer for a PEM fuel cell

A three-dimensional, steady state, single phase model is developed to study the mass and charge transfer within a proton exchange membrane (PEM) fuel cell. A single set of conservation equations is used for all PEM fuel cell layers and the governing equations are solved numerically using a finite-volume-based computational fluid dynamics technique. The numerical results for the flow field, species transport and phase potential are presented for two designs, namely a PEM fuel cell with conventional and interdigitated flow fields for the reactant supply.     

Numerical analysis of improved water management of open-cathode proton exchange membrane fuel cells with a dead-ended anode by pulsating flow

Anode water management is critical for the efficient operation of proton exchange membrane fuel cells with a dead-ended anode. To clarify the mass transfer phenomenon in the anode flow channel under the dead-ended anode mode, and reveal the influence mechanism of pulsating flow on water management, a three-dimensional, two-phase, non-isothermal transient model is established in this study. The water content and species distribution in different layers are analyzed, and the internal relationship between water transport behavior and output performance of the proton exchange membrane fuel cell under different operating conditions is explored. The simulation results show that the output performance of the proton exchange membrane fuel cell in dead-ended anode mode is directly related to the gas diffusion layer's water saturation and the hydrogen mass transfer. Furthermore, pulsating flow can effectively suppress the back diffusion of water, and improve the mass transfer rate of hydrogen. Consequently, the water management and the operational stability of the proton exchange membrane fuel cell are significantly improved. The research results of this paper have important guiding significance for improving the water and gas management of fuel cells.     

A three-dimensional mixed-domain PEM fuel cell model with fully-coupled transport phenomena

A three-dimensional mixed-domain PEM fuel cell model with fully-coupled transport phenomena has been developed in this paper. In this model, after fully justified simplifications, only one set of interfacial boundary conditions is required to connect the water content equation inside the membrane and the equation of the water mass fraction in the other regions. All the other conservation equations are still solved in the single-domain framework. Numerical results indicate that although the fully-coupled transport phenomena produce only minor effects on the overall PEM fuel cell performance, i.e. average current density, they impose significant effects on current distribution, net water transfer coefficient, velocity and density variations, and species distributions. Intricate interactions of the mass transfer across the membrane, electrochemical kinetics, density and velocity variations, and species distributions dictate the detailed cell performances. Therefore, for accurate PEM fuel cell modeling and simulation, the effects of the fully-coupled transport phenomena could not be neglected.     

Parametric and optimization study of a PEM fuel cell performance using three-dimensional computational fluid dynamics model

A full three-dimensional, non-isothermal computational fluid dynamics model of a proton exchange membrane (PEM) fuel cell with straight flow field channels has been developed. This comprehensive model accounts for the major transport phenomena in a PEM fuel cell: convective and diffusive heat and mass transfer, electrode kinetics, and potential fields. The new feature of the algorithm developed in this work is its capability for accurate calculation of the local activation overpotentials, which in turn results in improved prediction of the local current density distribution. The model is shown to be able to understand the many interacting, complex electrochemical, and transport phenomena that cannot be studied experimentally. This model is used to study the effects of several operating, design, and material parameters on fuel cell performance. Detailed analyses of the fuel cell performance under various operating conditions have been conducted and examined. The analysis helped identifying critical parameters and shed insight into the physical mechanisms leading to a fuel cell performance under various operating conditions.     

Simulation of the water and heat management in proton exchange membrane fuel cells

A non-isothermal and three-dimensional numerical model of a PEM fuel cell was developed to compute the water and heat management. Transport of water in the polymer membrane, phase change of water in the cathode porous medium and capillary flow to the gas channels were determined. Influences of these phenomena on fuel cells and conditions that may affect their performance have been numerically evaluated. Output variables are velocity, temperature, mass fraction, current density, voltage loss, water content of the polymer membrane, saturation and liquid flow fields. Cell voltage and total current density of PEM fuel cell were computed as well. Results show that there may be severe mass transfer limitations depending either on the design or on the water management of the cell. For the chosen conditions, the polymer membrane can keep and even increase its water content, as long as inlet flows are injected at 100% relative humidity. In case the fuel cell is operated under dehydrating conditions, the decrease of the water content of the polymer electrolyte may affect the performance. The variations of temperature were small. However, temperature plays an important role in the cathode reaction rate of the cell and in the dehydration of the polymer membrane. Numerical results and experimental data were found to be in good agreement.     

Flow rate and humidification effects on a PEM fuel cell performance and operation

A new algorithm is presented to integrate component balances along polymer electrolyte membrane fuel cell (PEMFC) channels to obtain three-dimensional results from a detailed two-dimensional finite element model. The analysis studies the cell performance at various hydrogen flow rates, air flow rates and humidification levels. This analysis shows that hydrogen and air flow rates and their relative humidity are critical to current density, membrane dry-out, and electrode flooding. Uniform current densities along the channels are known to be critical for thermal management and fuel cell life. This approach, of integrating a detailed two-dimensional across-the-channel model, is a promising method for fuel cell design due to its low computational cost compared to three-dimensional computational fluid dynamics models, its applicability to a wide range of fuel cell designs, and its ease of extending to fuel cell stack models.     

A single-phase, non-isothermal model for PEM fuel cells

A proton exchange membrane (PEM) fuel cell produces a similar amount of waste heat to its electric power output, and tolerates a small temperature deviation from its design point for best performance and durability. These stringent thermal requirements present a significant heat transfer problem. In this work, a three-dimensional, non-isothermal model is developed to account rigorously for various heat generation mechanisms, including irreversible heat due to electrochemical reactions, entropic heat, and Joule heating arising from the electrolyte ionic resistance. The thermal model is further coupled with the electrochemical and mass transport models, thus permitting a comprehensive study of thermal and water management in PEM fuel cells. Numerical simulations reveal that the thermal effect on PEM fuel cells becomes more critical at higher current density and/or lower gas diffusion layer thermal conductivity. This three-dimensional model for single cells forms a theoretical foundation for thermal analysis of multi-cell stacks where thermal management and stack cooling is a significant engineering challenge.     

Three-dimensional computational fluid dynamics model of a tubular-shaped PEM fuel cell

A full three-dimensional, non-isothermal computational fluid dynamics model of a tubular-shaped proton exchange membrane (PEM) fuel cell has been developed. This comprehensive model accounts for the major transport phenomena in a PEM fuel cell: convective and diffusive heat and mass transfer, electrode kinetics, and potential fields. In addition to the tubular-shaped geometry, the model feature an algorithm that allows for more realistic representation of the local activation overpotentials which leads to improved prediction of the local current density distribution. Three-dimensional results of the species profiles, temperature distribution, potential distribution, and local current density distribution are presented. The model is shown to be able to understand the many interacting, complex electrochemical, and transport phenomena that cannot be studied experimentally.     

Novel gas distributors and optimization for high power density in fuel cells

A novel gas distributor for fuel cells is proposed. It has three-dimensional current-collecting elements distributed in gas-delivery fields for effective current collection and heat/mass transfer enhancement. An analysis model has been developed in order to understand the performance of the output power density when the dimensions and distributive arrangement of the current collectors are different. Optimization analysis for a planar-type SOFC was conducted in order to outline the approach in optimizing a gas-delivery field when adopting three-dimensional current-collecting elements in a fuel cell. Experimental test of a proton exchange membrane (PEM) fuel cell adopting the novel gas distributor was conducted for verification of the new approach. Significant improvement of power output was obtained for the proposed new PEM fuel cells compared to the conventional ones under the same conditions except for the different gas distributors. Both the experimental results and modeling analysis are of great significance to the design of fuel cells of high power density.