温度、压力和湿度对质子交换膜燃料电池性能的影响

以Nafion质子交换膜燃料电池(PEMFC)为对象，通过测量电池的电流—电压、电流—功率和电压—时间曲线，研究了温度、压力和湿度等条件对电池性能的影响，同时也考察了电池的能量转换效率及短期运行时的稳定性，得出了电池较佳的工作条件。实验和计算结果表明：在反应温度为72℃、H2和02压力分别为0．2MPa、进气湿度饱和时，电池最大输出功率可达0．7W．cm^-2；在0．3W.cm^-2～0．7W．cm^-2范围内电池能量转换效率为62％—34％；在大电流密度下电池仍能稳定工作。     

质子交换膜燃料电池的水热管理

质子交换膜燃料电池电化学反应生成电能、热能和水。质子交换膜燃料电池中水管理与热管理是紧密关联互相耦合的,有效的水热管理对于提高电池的性能和寿命起着关键作用。本文对膜中水的迁移机理及影响水平衡的主要因素进行了分析,对目前较为有效的水管理方法进行了综述。另外,分析了在微重力条件下燃料电池水管理问题的重要性。燃料电池中约有40%~50%的能量耗散为热能,必须采取有效的散热方式及时排除这些热量。本文对质子交换膜燃料电池的温度分布、局部换热系数及散热等燃料电池热管理相关问题进行了分析。     

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。     

质子交换膜燃料电池膜电极组件温度分布的神经网络预测模型

质子交换膜燃料电池膜电极组件表面的温度分布会影响质子交换膜燃料电池的性能、寿命和可靠性.为探究质子交换膜燃料电池传热规律,本文提出了一种基于神经网络的质子交换膜燃料电池膜电极组件温度分布的预测模型.本研究选取径向基函数神经网络(RBF)和广义回归神经网络(GRNN)两种神经网络,以电流密度、温度点的位置作为网络输入,不同位置的温度作为网络输出,对平行流道质子交换膜燃料电池、蛇形流道质子交换膜燃料电池分别建立了神经网络预测模型.结果显示,RBF神经网络预测的均方根误差平均为0.464、平均绝对百分误差为1.179％,GRNN神经网络预测的均方根误差平均为0.7155、平均绝对百分误差为2.27％;相较于GRNN神经网络,RBF神经网络精度更高;基于RBF神经网络的平行流道质子交换膜燃料电池膜电极组件温度分布预测模型预测值与96％的实验值的相对误差在5％以内.基于RBF神经网络的蛇形流道质子交换膜燃料电池膜电极组件温度分布预测模型预测值与95％的实验值的相对误差在5％以内.     

质子交换膜燃料电池建模及水热传输特性分析

针对质子交换膜燃料电池(PEMFC)水管理开展了研究,建立了一维非等温两相流解析模型,研究了不同电流密度、微孔层接触角和不同加湿方案对电池内部水分布和温度分布的影响,提出了更好的进气加湿方案。结果表明:电流密度增大会导致阳极拖干、阴极水淹加剧,导致电池各部分温度上升。因各层材料亲水性不同,在交界面处能观察到液态水阶跃现象。增大微孔层接触角促进阴极液态水反扩散到阳极,一定程度上缓解阳极变干,但过大的接触角可能导致阴极水淹加剧。通过采取"阳极充分加湿、阴极低加湿"的进气加湿方案可以有效提高电池性能,并且能在一定程度改善电池内部受热,提高电池使用寿命。     

温度波动对质子交换膜燃料电池的影响

为了研究温度波动对质子交换膜燃料电池性能的影响,文章提出了一种新的温度计算模型——温度波动模型。将温度波动模型通过自定义函数导入计算流体动力学软件(Fluent)上进行仿真计算,并建立燃料电池试验测试系统,对工作温度为60℃,进气温度分别为43,50,55℃的电池性能进行测试。通过对Fluent模型、温度波动模型和试验值的比较发现:随着进气温度的升高,温度波动趋于平缓,燃料电池的性能逐渐增强;温度波动模型能够较准确地预测燃料电池的性能,尤其在进气温度为43℃、电流密度为1.088 A/cm2时,其误差比Fluent模型减少30%。     

均匀磁场对质子交换膜燃料电池工作性能影响研究

通过在质子交换膜燃料电池加载不同方向、不同强度的均匀磁场,研究均匀磁场对质子交换膜燃料电池工作性能的影响。研究发现,在燃料电池两侧加载不同方向、不同强度的均匀磁场,可以不同程度提升质子交换膜燃料电池的工作性能。文章对比了磁场方向与质子交换膜燃料电池双极板两侧平行及垂直时的工作性能,垂直磁场下的电池输出功率和工作电流提升幅度最大。当质子交换膜燃料电池分别置于不同强度(270,440,530 m T)的均匀磁场时,磁场下的电池输出功率与不加载磁场时有所增大,并且随着外加均匀磁场的增大,电池的输出功率也随之提高。     

质子交换膜燃料电池内电荷传递的数值模拟

为深入研究质子交换膜燃料电池内电荷传递的规律,发展了一个三维的单相流、非等温数学模型,模型考虑了电子在催化层和扩散层、质子在催化层和质子交换膜中的传递。通过计算得到了电池内电位和电流密度的空间分布,分析了不同电极结构参数下电流密度的分布和最终造成的性能差异。结果表明,欧姆电位的下降主要发生在膜相电位,而碳相电位的下降几乎可以忽略不计;电流密度在流道与集电极交界处出现＂火焰形＂累积效应;改变电池的结构对电池性能影响不大,应结合加工成本和电流密度分布综合考虑。     

小型质子交换膜燃料电池的增湿技术研究

分析了PEMFC电池内部水的生成和转移过程，列举了各种增湿方法，指出了几种外增湿法对小型氢空质子交换膜燃料电池进行增湿的优缺点和对电池性能的影响。     

四流道蛇形结构质子交换膜燃料电池温度分布数值模拟

为研究温度对质子交换膜燃料电池性能的影响,运用多物理场直接耦合分析软件COMSOL Multiphysics,对不同电池温度的四流道蛇形流场质子交换膜燃料电池进行了数值模拟。模拟得到了不同电池温度下垂直膜电极平面以及电池中心处从阳极流道到膜,再到到阴极流道的温度变化情况;还得到了电池温度为353K时,电池入口处、中心处和出口处从阳极流道到阴极流道相应位置点的温差变化。对模拟结果进行分析和比较后发现:电池内部温度的升高与电池本身的原始温度存在线性变化关系;电池入口处、中心处和出口处的温度变化趋势存在差异,且电池入口处温升最大,中心处次之,出口处温升最小;随着电池温度的升高,电池因内部反应所产生的热量减少。模拟结果对质子交换膜燃料电池的性能优化有重要意义。     

Investigation of water transport through membrane in a PEM fuel cell by water balance experiments

Water balance in a polymer electrolyte membrane fuel cell (PEMFC) was investigated by measurements of the net drag coefficient under various conditions. The effects of water balance in the PEMFC on the cell performance were also investigated at different operating conditions. Experimental results reveal that the net drag coefficient of water through the membrane depended on current density and humidification of feed gases. It was found that the net drag coefficient (net number of water molecules transported per proton) ranged from −0.02 to 0.93, and was dependent on the operating conditions, the current load and the level of humidification. It was also found that the humidity of both anode and cathode inlet gases had a significant effect on the fuel cell performance. The resistance of the working fuel cell showed that the membrane resistance increased as the feed gas relative humidity (RH) decreased. The diffusion of water across Nafion membranes was also investigated by experimental water flux measurements. The electro-osmotic drag coefficient was evaluated from the experimental results of water balance and diffusion water flux measurements. The value of electro-osmotic drag coefficient, ranging from 1.5 to 2.6 under various operating conditions, was in agreement with literature values. The electro-osmotic drag coefficient, the net flux of water through the membrane and the effective drag as a function of operating conditions will also provide validation data for the fuel cell modeling and simulation efforts.     

Maintaining desired level of relative humidity throughout a fuel cell with spatially variable heat removal rates

A concept of using the product water to internally humidify the air stream in a PEM fuel cell without external humidification is investigated by a simple, pseudo 2-D model along a single channel. This model takes into account the mass and energy balance, water and heat generation rates, heat removal, and water transport through the membrane. The model and thus the concept were confirmed experimentally using a 5-segment fuel cell. The temperature of each segment could be individually controlled, and the temperature and humidity of air could be measured between each segment. A temperature profile has been established, by applying spatially variable heat removal rates along the cathode channel, that results in relative humidity being close to 100% throughout the cell without any external humidification. The concept may be applied to a fuel cell stack resulting in simplification of the suporting system by avoiding external humidification.     

Dynamic fuel cell gas humidification system

Water management is one of the crucial factors regarding the performance and durability of low temperature PEM fuel cells. Amongst other factors, the water balance in an operating fuel cell can be influenced by the humidification of the reaction gases. For transient response investigations of the fuel cell behavior under fast humidification changes a system is needed which is able to humidify the supplied gases in a highly dynamic and reproducible way. Exact knowledge of the water content of the supplied gases is of utmost importance to study humidification effects. In this contribution, a dynamic fuel cell humidification system is presented. Reliability of the concept is proven by using three different methods: straightforward dew point measurements, electrochemical impedance spectroscopy (EIS) and in situ neutron radiography. The test setup is able to provide dew point temperatures with a tolerance range of 1–3 K leading to a highly reproducible fuel cell performance and water content of the complete cell.     

Improvement of PEMFC water management by employing water transport plate as bipolar plate

In this study, a porous hydrophilic water transport plate (WTP) has been employed as a bipolar plate to improve water management in proton exchange membrane fuel cells (PEMFCs). The electric conductivity, gas blocking property, water permeability and wettability of the WTP were characterized. The performance, electrochemical impedance spectroscopy (EIS) and water balance of fuel cells with WTPs and solid plates were evaluated. Benefiting from the humidification and drainage functions of the WTP, the performance of fuel cells with WTPs significantly improved compared with fuel cells with traditional solid plates. As indicated from the experiments, a WTP that was placed on the cathode side is favorable for cell performance and system complexity. Additionally, hydrogen stoichiometry hardly affects the water transport, whereas a decrease in air stoichiometry can switch the main function of the WTP from humidification to water drainage. The results show that the use of WTP technology is promising for water management improvement in PEMFCs.     

Three-dimensional two-phase flow model of proton exchange membrane fuel cell with parallel gas distributors

A non-isothermal, steady-state, three-dimensional (3D), two-phase, multicomponent transport model is developed for proton exchange membrane (PEM) fuel cell with parallel gas distributors. A key feature of this work is that a detailed membrane model is developed for the liquid water transport with a two-mode water transfer condition, accounting for the non-equilibrium humidification of membrane with the replacement of an equilibrium assumption. Another key feature is that water transport processes inside electrodes are coupled and the balance of water flux is insured between anode and cathode during the modeling. The model is validated by the comparison of predicted cell polarization curve with experimental data. The simulation is performed for water vapor concentration field of reactant gases, water content distribution in the membrane, liquid water velocity field and liquid water saturation distribution inside the cathode. The net water flux and net water transport coefficient values are obtained at different current densities in this work, which are seldom discussed in other modeling works. The temperature distribution inside the cell is also simulated by this model.     

Humidification studies on polymer electrolyte membrane fuel cell

Two methods of humidifying the anode gas, namely, external and membrane humidification, for a polymer electrolyte membrane fuel (PEMFC) cell are explained. It is found that the water of solvation of protons decreases with increase in the current density and the electrode area. This is due to insufficient external humidification. In a membrane-based humidification, an optimum set of parameters, such as gas flow rate, area and type of the membrane, must be chosen to achieve effective humidification. The present study examines the dependence of water pick-up by hydrogen on the temperature, area and thickness of the membrane in membrane humidification. Since the performance of the fuel cell is dependent more on hydrogen humidification than on oxygen humidification, the scope of the work is restricted to the humidification of hydrogen using Nafion^® membrane. An examination is made on the dependence of water pick-up by hydrogen in membrane humidification on the temperature, area and thickness of the membrane. The dependence of fuel cell performance on membrane humidification and external humidification in the anode gas is also considered.     

外界供给参数对PEMFC输出性能及水热平衡的影响

为了改善质子交换膜燃料电池(PEMFC)内部的水热平衡,从而进一步改善PEMFC的输出性能,文章建立了PEMFC的三维模型,通过改变PEMFC的外界供给参数(进气速度、加湿率以及冷却水流速),应用COMSOL模拟仿真得到了PEMFC的极化曲线和功率曲线、流道和气体扩散层(GDL)的水浓度分布情况,以及冷却水流速对PEMFC温度的影响。研究结果表明:随着进气速度和加湿率的逐渐增加,PEMFC的输出性能均逐渐提升,但是,过高的加湿率可能导致电极水淹;随着冷却水流速的增加,PEMFC温度加速下降,膜内温度分布变得更均匀。     

The effect of relative humidity of the cathode on the performance and the uniformity of PEM fuel cells

The effect of relative humidity of the cathode (RHC) on proton exchange membrane (PEM) fuel cells has been studied focusing on automotive operation. Computational fluid dynamics (CFD) simulations were performed on a 300-cm² serpentine flow-field configuration at various RHC levels. The dependency of current density, membrane water contents, net water flux on the performance and the uniformity was investigated. The uniformity of current density and temperature was evaluated by employing standard deviation. The water balance inside a fuel cell was examined by describing electro-osmotic drag and back diffusion. It was concluded that the RHC has strong effect on the cell performance and uniformity. The dry RHC showed low cell voltage and non-uniform distributions of current density and temperature, whereas high RHC presented increased cell performance and uniform distributions of current density and temperature with well-hydrated membrane electrode assembly (MEA). Also the local current density distribution was strongly dependent on the local membrane water contents distribution that has complex phenomena of water transport. The elimination of external humidifier is desirable for the automotive operation, but it could degrade cell performance and durability due to dehydration of the MEA. Therefore a proper humidification of the reactant is necessary.     

增湿活化脱硫试验研究

在热态脱硫试验台上进行了喷水活化和蒸汽活化脱硫试验,并研究了在不同钙硫比,饱和温距、SO2浓度和烟气速度下的脱硫性能,研究表明,与单纯的吸收剂喷射技术相比,蒸汽增湿活化和喷水增湿活化,都可以提高脱硫效率,但喷水活化效果比蒸汽活化效果好得多,而且脱硫效率随钙硫比增加,饱和温距、SO2浓度及烟气速度的降低而升高;在喷水增湿活脱硫中,脱硫剂浆滴的脱硫作用远远大于脱硫剂吸温脱硫作用。     

Influences of gas relative humidity on the temperature of membrane in PEMFC with interdigitated flow field

A fundamental understanding of the water balance of a fuel cell during operation is crucial for improving the cell performance and durability. The humidification in the anode or cathode has an important effect on the flow characteristics and cell efficiency. Three-dimensional steady mathematical model based on the electrochemical, current distribution, fluid motion continuity equation, momentum and energy equation, boundary layer theory has been developed to simulate PEMFC with interdigitated flow field using the computational fluid dynamics (CFD). Effects on the current density and temperature differences have been simulated and analyzed respectively, when the humidification in the anode or cathode is from 0% to 100% respectively. The numerical results show that the humidification strongly influences the current density and temperature difference so as to affect the cell efficiency. Under the same operation conditions and low humidification conditions, anode humidification can better enhance the performance of the battery and improve the extent of PEM humidification.