Analysis of GDL flooding effects on PEMFC performance

One of the major concerns of the gas diffusion layer (GDL) inside a proton exchange membrane fuel cell (PEMFC) is water management. Treatment of the pores of the GDL can affect the PEMFC performance due to the degree of water flooding inside the GDL. In this work, GDL flooding was investigated using a simplified approach in an established numerical model. The predictions are compared with experimental data of GDLs with different treatments. Local distributions inside the cell are given and the effect of homogenous GDL flooding on these is discussed.     

Membrane performance comparison in a proton exchange membrane fuel cell (PEMFC) stack

A 5-cell proton exchange membrane fuel cell (PEMFC) stack with different types of membrane electrode assemblies (MEAs) was tested to compare their performances and electrochemical characteristics. The experimental data were obtained with a stack of 5 cells and active area of 125 cm². The stack consisted of different Nafion^® and hydrocarbon membranes with the same types of electrocatalyst. The membranes were installed in different cells and in the same stack. Polarization and voltage measurement data were obtained to compare their performances at different temperatures and anode humidity conditions. Also, impedance spectroscopy data were obtained in similar manner to compare the differences in their resistance.     

PEMFC电堆动态工况响应性能试验

质子交换膜燃料电池（PEMFC）电堆动态响应特性对PEMFC电堆的耐久性和可靠性具有很大影响。本文试验考察了PEMFC电堆在动态工况下的输出性能、单电池电压均衡性变化和动态响应特性。结果表明,在整个动态运行工况下,电堆运行良好,进出口冷却液温差小于5℃。电流阶跃变化时电堆电压均衡性出现突增变化,同时随着电流的增大,稳态时电堆均衡性变差。在超负荷（200A）运行工况下,电堆各单电池之间输出差异变大,均衡性持续变差,电堆中间和前端单电池电压明显降低。此外,在整个动态响应过程中电流阶跃上升时的电压最大下冲值比电流阶跃下降时的电压最大上调量大,但输出电压能在10s内达到相对稳定的状态（电压波动率＜0.02）。通过该研究,以期为实际车载电堆运行和控制优化提供参考。     

Analysis of PEM fuel cell stacks using an empirical current–voltage equation

An empirical equation was developed to describe the electrode processes (activation, ohmic and mass-transfer) of PEMFC stacks over the entire current range. The potential–current and power–current curves of a strip PEMFC stack were fitted with the empirical equation under a variety of experimental humidity, temperature and stack length conditions. The concept of mass transfer impedance was defined mathematically in the present research. For the strip PEMFC stack, mass transfer impedance was only important at high currents. With decreasing humidity the mass transfer impedance increased considerably. With increasing temperature or stack cell number the mass transfer impedance increased only slightly.     

Operation characteristics of portable direct methanol fuel cell stack at sub-zero temperatures using hydrocarbon membrane and high concentration methanol

Cold start and operation of a direct methanol fuel cell (DMFC) are investigated at sub-zero temperatures by using a 10-cell stack. The stack is manufactured with a hydrocarbon membrane to minimize the methanol crossover problem, which can be caused by use of high concentration methanol solutions. The stack is heated up for the cold start and operation only by heat of the exothermic reactions without any heating device and additional insulation means, to examine operation characteristics of the DMFC stack at low temperatures. The concentration of methanol solutions is selected in the range of 3-8 M, considering the freezing points of the solution for corresponding operation temperatures (−5 to −15 °C). Although the DMFC stack undergoes a sharp voltage drop and a significant performance decrease at the initial stage of the frozen condition, the self-heating DMFC are successfully operated at −5 and −10 °C in both constant current or constant voltage modes. The cold start-up time also is nearly independent of the operating modes. In contrast, the stack at −15 °C is barely started up only by a constant voltage mode with some voltage fluctuation. The DMFC stack after the cold operation exhibits the performance loss of about 45%. Such performance loss is mainly caused by degradation of the electrocatalysts.     

空冷型PEMFC电堆阴极风扇系统实验与模拟

风扇被用于空冷型PEMFC电堆的冷却和氧气的供应,空气流速的大小和分布对于提高电堆输出性能和内部温度的均匀性非常关键,可以通过改变风扇的工作电压(风扇工作在恒流模式)和风扇与PEMFC阴极入口的距离来调整。针对实验室自制空冷型PEMFC电堆进行实验来寻找风扇工作距离和工作电压对于电堆性能的影响,并利用多元回归拟合得到以电堆表面平均温度为因变量,以风扇工作电压和风扇工作距离为自变量的经验公式。研究结果表明:当风扇工作距离大于或小于其最优工作距离时,电堆性能均会发生衰减;当风扇处于最优工作距离时,电堆表面温度更加均匀,各单电池电压均匀性得到提高,并且此时所需的最优风扇工作电压更小。该研究对于提高空冷型PEMFC电堆输出性能、增加电堆运行稳定性、提高电堆系统效率等具有重要的指导和参考价值。     

基于改进遗传算法的PEMFC电堆温度模型建模

针对质子交换膜燃料电池（PEMFC）系统过于复杂、难以建模,而已建立的数学模型由于电堆使用的材料、结构不同,模型参数相差甚远,无法统一给出一个具有代表性的高精度的PEMFC电堆模型,难以满足PEMFC控制系统设计和应用的要求.本文从实际应用角度出发,利用传热学、流体动力学知识建立了一个千瓦级的PEMFC电堆温度模型.由于模型中一些关键参数无法由实验精确测出,但它们对模型精度的影响极大,所以需要找出一个能够高精度辨识模型参数的方法来解决这个问题.文章中提出的改进遗传算法具有良好的全局和局部的搜索、优化能力,能够高精度地辨识这些参数.仿真和实验结果验证了模型的实用性和可靠性.     

A study on the start-up and performance of a kW-class molten carbonate fuel cell (MCFC) stack

A kW-class internal-manifolded molten carbonate fuel cell (MCFC) stack (52 cells) was assembled with inorganic adhesive under a suitable stacking pressure. The organic compounds in the matrices were burnt out under the conditions of slow and uniform elevation of temperature and big flow of oxygen gas in the stack. The stacking pressure dropped with elevating temperature. The output power of the stack at 150 mA cm⁻² was 1025.5 W when the reactant gas pressure and utilization were 0.5 MPa and 20%, respectively. The thermal-electrical efficiency of the stack was enhanced by increasing the pressure of the reactant. However, it was contrarily decreased when current density was increased.     

Membrane fuel cells - concepts and system design

The low power range can be an interesting application market for the PEM fuel cell in the near future. With a possible function as battery in portable devices the banded structure PEM fuel cell will be an advantageous alternative to the conventional stack. The new system provides high output voltages, a flat cell geometry and can be optimized with respect to smaller cell volumes. The article describes the principle function of such a system and the necessary parameter for optimizing the cell geometry. A comparison with a conventional stack design is given and experimental results with an eight cell banded structure stack are presented.     

Development and operation of a 150 W air-feed direct methanol fuel cell stack

A five-cell 150 W air-feed direct methanol fuel cell (DMFC) stack was demonstrated. The DMFC cells employed Nafion 117^® as a solid polymer electrolyte membrane and high surface area carbon supported Pt-Ru and Pt catalysts for methanol electrooxidation and oxygen reduction, respectively. Stainless steel-based stack housing and bipolar plates were utilized. Electrodes with a 225 cm² geometrical area were manufactured by a doctor-blade technique. An average power density of about 140 mW cm^–2 was obtained at 110 °C in the presence of 1 M methanol and 3 atm air feed. A small area graphite single cell (5 cm²) based on the same membrane electrode assembly (MEA) gave a power density of 180 mW cm^–2 under similar operating conditions. This difference is ascribed to the larger internal resistance of the stack and to non-homogeneous reactant distribution. A small loss of performance was observed at high current densities after one month of discontinuous stack operation.     

PEMFC膜电极组成及其性能

质子交换膜燃料电池(PEMFC)的膜电极(MEA)由质子交换膜、催化层、水管理层(WML)和扩散层组成。研究了WML的厚度和聚四氟乙烯(PTFE)的含量对膜电极性能的影响,并采用了两种新型造孔剂(碳酸氢铵和硫酸铵)优化WML的孔结构。采用环境扫描电镜(ESEM)表征了膜电极的表面形貌和孔结构;采用单体PEMFC的电流密度-电压曲线评价了膜电极在外增湿和自增湿方式下的极化特性,结果表明,WML的建立提高了膜电极的水管理能力,使膜电极在自增湿方式下具有良好的极化特性。     

Experimental and numerical simulation studies on diesel pool fire

Experimental studies are performed under different ventilation conditions to investigate the effect of ventilation on compartment fires. A compartment of size 4 m × 4 m × 4 m having a door of size 2 m × 1 m is used for experiments. The experiments are conducted with full door open and half door open conditions. Diesel, used as a fuel source, is placed in a pan of 40 cm diameter and 15 cm height, which is kept in the center of the compartment. During experiments a constant 12 cm height of the fuel is maintained above the pan bottom. The maximum heat release rate is found to be 100 kW and 115 kW in full door open and half door open experiments respectively. It is observed that the size of door opening affected the heat release rate, burning rate and thermal environment inside the compartment after the growth period of 800 s. The numerical simulation is also performed for full door open experiment using CFD code, Fire Dynamics Simulator (FDS, version 6.0.1) developed by NIST. Simulation is accomplished with the refinement of mesh size near the fire source; results from FDS closely match with the experimental results. Copyright © 2016 John Wiley & Sons, Ltd.     

阴、阳极加湿程度对PEMFC内部传质的影响

为了研究常规流场下阴、阳极增湿程度对电池内部水分布、传递、膜性能及水拖曳系数等的影响,对PEMFC进行二维建模,应用控制容积法对控制方程进行离散,然后求解,得到了电池内部水和反应气浓度、速度分布、膜中电流密度、电势分布及膜中水分布,考察了气体不同增湿程度对质子交换膜电导率及电池内部传质的影响.结果表明,PEMFC中水综合拖曳系数随着阳极加湿程度的增加而增大,随阴极增湿程度的增加而减小,但阳极增湿对水综合拖曳系数的影响比同增湿程度下阴极增湿对水综合拖曳系数的影响大得多.同时,随着阳极加湿程度的升高,质子交换膜（PEM）电导率急剧升高,而阴极加湿程度对PEM电导率的影响只是停留在较小的电流范围之内.故PEMFC在小电流密度工作时,应该使阳极气体充分增湿;而在大电流密度工作时,应该适当降低阳极的增湿程度以降低阴极两相流的机会,从而改善阴极的传质状况.     

PEMFC用Pt纳米线阴极催化剂的制备及在电堆中的应用

采用无模板法制备了用于质子交换膜燃料电池（PEMFC）的碳载铂纳米线（Pt NWs/C）阴极催化剂,使用透射电镜（TEM）和X射线衍射图谱技术（XRD）对催化剂的微观结构和形貌进行了表征。研究结果表明,制备的铂催化剂具有纳米线的结构,平均截面直径为（4.0±0.2）nm,线长为15～25 nm。利用循环伏安（CV）法和线性伏安扫描法（LSV）表征催化剂的电化学活性和氧还原反应（ORR）特性,结果表明制备的Pt NWs/C催化剂电化学特性良好。利用Pt NWs/C和Pt/C作为阴极催化剂制备膜电极（MEA）,并进行测试,最大功率密度分别为705.6 mW·cm^-2和674.4 mW·cm^-2。然后以Pt NWs/C和Pt/C为阴极催化剂组装了18片和20片的电堆,并进行性能测试,电堆的最大功率密度分别为409.2 mW·cm^-2和702.7 mW·cm^-2,单电池电压差异系数（C_v）分别为16.1%和4.36%,这表明Pt NWs/C作为阴极催化剂在放大后的膜电极组件（MEA）里表现出较好的催化活性,但与商业催化剂相比其性能与均一性还有待提高。该研究可为Pt NWs/C催化剂放大制备提供依据,同时可为后续的基于Pt NWs/C的电堆的耐久性测试和车载应用奠定基础。     

Comparative studies of a single cell and a stack of direct methanol fuel cells

Comparative studies have been conducted to observe the characteristics of a single cell and a stack of direct methanol fuel cells (DMFC) at ambient conditions. The maximum power density of a single cell was about 70 mW/ cm² at 2M methanol (CH₃OH) of 3.75 cc/min and dry air of 250 cc/min at room temperature and atmospheric pressure. In a stack, on the other hand, the maximum power density of the stack was 85mW/cm² which was about a 20% higher value. This could be attributed to higher internal temperature than that of the single cell: the temperature of single cell increased up to 35 °C, while the highest temperature of the stack was 69 °C. This is because the cell temperature in DMFC was autonomously increased by exothermal reaction such as chemical oxidation of CH₃OH and oxygen reduction. The temperature was strongly dependent on the number of unit cells in a stack and the amount of electric load applied. In DMFC stacks, the performance of an individual cell showed uneven distribution when the electric load was increased and it was mostly influenced by different local concentration of reactants and non-uniform temperature     

微流道气-液两相流研究及其在PEMFC中的应用进展

微流道由于具有比表面积高、传质能力强等优点,已成功地应用于化工领域的多种气-液反应体系中。此外,其在化工领域中的研究成果还可以应用于目前备受关注的燃料电池领域以提高其电化学转化效率。然而,微流道尺度的微小化以及其中气-液两相流规律的复杂性使得微流道内的气-液两相流特性的阐明还需要进一步的研究,才能促使微流道在实际应用中发挥更优异的作用。本文从流型、压降和传质三个关键特征的研究角度来介绍微流道内气-液两相流的研究进展,简述了不同流型的特征及其形成条件,阐明了其对应的压降大小和传质能力的高低,回顾了现有的压降和传质系数的预测模型及其相应的优化措施,并分析了运用这三个关键特征的相关参数来优化质子交换膜燃料电池流场设计方面的研究进展,得到了流场类型、流道尺寸、流道形状、流道表面特性等的优化方案。但是,燃料电池中的精细流道的特殊结构及其特定工况使得其与传统的微流道有显著的区别。由此,本文提出了应当根据燃料电池精细流道的特点探明其中的两相流型、压降和传质的动态变化规律以及构建相应的压降预测模型的建议,以期为流场设计提供更准确的参考依据,进而提高燃料电池性能,加速燃料电池的商用进程。     

基于水泥除尘+脱硝流场的CFD数值模拟研究

随着社会环保意识的增强,大气污染物的排放标准也日益严格,这给环保工程带来了极大的潜在市场。脱硝反应器设计作为SCR脱硝工艺中除了催化剂的另一核心,在水泥行业没有更好的催化剂被研发出来之前,想要脱硝设备的性能得到极佳的发挥,在高温高尘区布置除尘+脱硝设备已经是工程上的一个选择,而在高尘区要保证催化剂的稳定、高效运行,流场的优化必不可少。本文针对某水泥行业除尘+脱硝项目,采用CFD软件对其流场进行数值模拟,并给出导流板的优化设计方案。结果表明:在电除尘器上进气口布置合适的导流板,使得进入电场的烟气分布均匀;同时在整流格栅前添加导流板,脱硝反应器内的流场也得到了极大改善。因此,采用CFD软件数值模拟对水泥行业除尘+脱硝有着重要的意义。     

Performance and stability of Pt-based ternary alloy catalysts for PEMFC

Carbon-supported Pt-based ternary alloy electrocatalysts were prepared by incipient wetness method in order to elucidate the origin of the enhanced activity of oxygen reduction reaction in PEMFC. To measure the catalytic activity and stability of the cathode alloy catalysts (electrodes containing Pt loading of 0.3 mg/cm², 20 wt.% Pt/C, E-TEK), the I-V polarization curves were obtained. All alloy catalysts showed higher performances than Pt/C. It can be concluded that as platinum formed alloys with transition metals, the electronic state of Pt and the nearest neighbor Pt-Pt distance changes, which significantly influence the electrocatalytic activity for oxygen reduction.Long-term stability test was performed with the Pt₆Co₁Cr₁/C alloy catalyst for 500 h. According to XPS analysis, the lower oxide component with Pt₆Co₁Cr₁/C electrocatalyst provides a large portion of platinum in metallic species in the electrocatalyst and it seems to be mainly responsible for its enhanced activity towards oxygen reduction.     

燃料电池的进展

本文介绍了燃料电池的特点和类型,以及燃料电池在各领域的应用前景和国内外研究进展情况,并对我国燃料电池发展提出了参考建议。