扩散层孔隙率对PEMFC性能影响的模拟研究

为了研究扩散层孔隙率对质子交换膜燃料电池(PEMFC)性能的影响,采用COMSOL软件,通过数值模拟得出气体扩散层不同孔隙率(0.2,0.4,0.6和0.8)时,单直通道和具有楔形肋片(长1 mm,高1.5 mm,宽2 mm)的PEMFC性能曲线、阴极氧气质量分数分布和水质量分数分布。结果表明:扩散层孔隙率对燃料电池性能具有较大影响,随着扩散层孔隙率从0.2增大到0.8,PEMFC的电流密度逐渐增加,最大可达847 mA/cm~2;相对于单直通道,增加孔隙率比添加楔形肋片更利于提升电池性能;在孔隙率为0.6和0.8时,氧气更易扩散到反应区,排水效果更好。     

PEMFC温度的自动控制

本文分析了工作温度对质子交换膜燃料电池(PEMFC)运行性能的影响,研究采用Nafion膜作为温度传感器来检测质子交换膜燃料电池的工作温度,运用闭环负反馈调节方案实现了质子交换膜燃料电池温度的自动控制,并对温度调节过渡过程的性能指标进行了分析和验证。     

气体扩散层结构对PEMFC性能影响二维数值模拟

质子交换膜燃料电池在运行过程中反应物从流道传输至催化层时会经过气体扩散层,气体扩散层即 可用来传输反应气体,又用来排出反应物生成的水,所以探究气体扩散层的结构对参加反应的物质及生成物 传输的影响规律有助于了解其分布情况。通过数值模拟比较了穿孔型、树状型和不规则形状气体扩散层在不 同孔隙率下顺流流动时对电池性能的影响情况。计算结果表明,气体扩散层结构严重影响质子交换膜燃料电 池性能,三种不同形状的气体扩散层对应的电性能随孔隙率的变化规律各不相同,到达催化层表面氧气的含 量受扩散层结构影响比氢气大,气体扩散层结构对阴极侧生成物水含量的影响不可忽略。     

不同流场结构对PEMFC性能影响的模拟研究

该文模拟常规矩形平行流场、正六边形平行流场和正六边形蜂窝状仿生学流场对质子交换膜燃料电池（PEMFC）性能的影响。通过对极化曲线、氧气和水分布、膜电流密度以及压降和寄生功率密度进行分析,结果表明：正六边形流场表现出良好的输出性能,且正六边形蜂窝状流场的电流密度比常规矩形平行流场和正六边形平行流场分别提升11.28%和4.95%。此外,常规矩形平行流场、正六边形平行流场和正六边形蜂窝状流场的氧气不均匀度分别为0.64、0.53和0.41,正六边形蜂窝状流场展现出更好的水和膜电流密度分布能力,进一步说明正六边形流场缓解了氧气、水和膜电流密度分布不均匀的问题。正六边形蜂窝状流场压降虽比常规矩形平行流场和正六边形平行流场分别增加40.0%和27.7%,有较高的寄生功率密度,但仍获得了最大的净输出功率密度。     

基于ALMBO算法的PEMFC分数阶时域子空间模型研究

针对质子交换膜燃料电池（PEMFC）发电过程复杂难以建模的问题,考虑PEMFC系统的分数阶特性,提出一种基于优化的分数阶时域子空间辨识方法,并建立PEMFC的分数阶状态空间模型。首先,将分数阶微分理论与子空间时域辨识方法相结合,采用Poisson滤波器对输入输出信号进行滤波处理,并引入权重矩阵提高辨识的精度;其次,对Poisson滤波器以及辨识的分数阶阶次寻优,提出一种变异反向学习的自适应帝王蝶优化算法（ALMBO）,在迁移算子中引入变异反向学习策略、并融入自适应权重来提高寻优的精度,防止陷入局部最优解。最后,通过仿真结果验证算法的有效性,所得的PEMFC辨识模型能准确描述PEMFC的动态过程。     

质子交换膜燃料电池（PEMFC）最新进展

评述了质子交换膜燃料电池的发展背景、最新进展、目前发展障碍和我国发展现状。     

车用PEMFC直流道散热特性研究

质子交换膜燃料电池(PEMFC)的散热对其性能有很大影响。文章利用Gambit软件建立带冷却通道的PEMFC模型,使用计算流体力学软件Fluent中的PEM模块进行数值模拟计算。通过改变冷却通道进口处冷却水的流速和温度,对质子交换膜内温度和冷却水出口处温度进行了分析。数据表明,冷却水的流速和温度对PEM内温度分布都有一定影响。为使PEMFC正常稳定工作,冷却水流速不宜过小、温度不宜过低。     

质子交换膜燃料电池(PEMFC)的产业化开发

本文简述了燃料电池的研发概况;综述了国内、外质子交换膜燃料电池(PEMFC)的技术状态;分析了PEMFC关键技术及其在商品化过程中存在的主要问题;研究了PEMFC产业化开发的方向;认为我国应加强PEMFC的开发力度,加速它的产业化进程.     

小型PEMFC电源系统热设计实验研究

通过实验研究了利用燃料电池产生的废热以强制对流传热的方式给金属氢化物储氢器加热的可行性与具体的设计方案,与目前已报道的国内外便携式PEMFC系统相比,该方案无任何附属设备,使系统保持较高的整体效率,提高了金属氢化物储氢器的放氢性能.通过正交实验和实验数据的方差分析得知该方案在保证金属氢化物储氢器持续放氢的同时,对PEMFC无明显负面影响.     

车用PEMFC直流道散热特性研究

本文利用Gambit软件建立了带冷却通道的质子交换膜燃料电池（PEMFC）模型,使用计算流体力学软件Fluent中的PEM模块进行数值模拟计算。改变冷却通道进口处冷却水的流速和温度,对质子交换膜内温度和冷却水出口处温度进行了分析,其结果为PEMFC优化提供依据。     

Numerical study for in-plane gradient effects of cathode gas diffusion layer on PEMFC under low humidity condition

A numerical study about in-plane porosity and contact angle gradient effects of cathode gas diffusion layer (GDL) on polymer electrolyte membrane fuel cell (PEMFC) under low humidity condition below 50% relative humidity is performed in this work. Firstly, a numerical model for a fuel cell is developed, which considers mass transfer, electrochemical reaction, and water saturation in cathode GDL. For water saturation in cathode GDL, porosity and contact angle of GDL are also considered in developing the model. Secondly, current density distribution in PEMFC with uniform cathode GDL is scrutinized to design the gradient cathode GDL. Finally, current density distributions in PEMFC with gradient cathode GDL and uniform cathode GDL are compared. At the gas inlet side, the current density is higher in GDL with a gradient than GDL with high porosity and large contact angle. At the outlet side, the current density is higher in GDL with a gradient than GDL with low porosity and small contact angle. As a result, gradient cathode GDL increases the maximum power by 9% than GDL with low porosity and small contact angle. Moreover, gradient cathode GDL uniformizes the current density distribution by 4% than GDL with high porosity and large contact angle.     

Compress effects on porosity,gas‐phase tortuosity,and gas permeability in a simulated PEM gas diffusion layer

Among the parameters to take into account in the design of a proton exchange membrane fuel cell (PEMFC), the energy conversion efficiency and material cost are very important. Understanding in deep the behavior and properties of functional layers at the microscale is helpful for improving the performance of the system and find alternative materials. The functional layers of the PEMFC, i.e., the gas diffusion layer (GDL) and catalyst layer, are typically porous materials. This characteristic allows the transport of fluids and charges, which is needed for the energy conversion process. Specifically, in the GDL, structural parameters such as porosity, tortuosity, and permeability should be optimized and predicted under certain conditions. These parameters have effects on the performance of PEMFCs, and they can be modified when the assembly compression is effected. In this paper, the porosity, gas‐phase tortuosity, and through‐plane permeability are calculated. These variables change when the digitally created GDL is under compression conditions. The compression effects on the variables are studied until the thickness is 66% of the initial value. Because of the feasibility to handle problems in the porous media, the fluid flow behavior is evaluated using the lattice Boltzmann method. Our results show that when the GDL is compressed, the porosity and through‐plane permeability decrease, while the gas‐phase tortuosity increases, i.e., increase the gas‐phase transport resistance. Copyright © 2015 John Wiley & Sons, Ltd.     

Tomographic analysis of porosity variation in gas diffusion layer under freeze-thaw cycles

Synchrotron X-ray micro-computed tomography (X-ray μCT) is employed to measure the volume variation of gas diffusion layer (GDL) of a polymer electrolyte fuel cell (PEFC). In the present study, 3D structures are reconstructed by merging orthogonal-plane images. Using the 3D reconstruction, the variation of structural parameters such as the porosity in GDL is investigated under freeze-thaw cycles. The freez-thaw cycles are established using cryo system and light source, respectively. As a result, a structural transformation is observed at the interface between GDL and micro porous layer (MPL). In addition, the porosity is critically changed with irreversible transition under freeze-thaw cycles.     

Ultra thin gas diffusion layer development for PEMFC

This research studies an ultra-thin carbon fiber paper fabrication process for proton exchange membrane fuel cells (PEMFCs). Polyacrylonitrile (PAN) based carbon fibers 6 mm long were dispersed and formed at aerial weights of 15 and 20 g/m² using a slurry molding machine. Polyscrylamide (PAM) and polyvinyl alcohol (PVA) dispersal agent solutions for fiber binding were added to evenly distribute the carbon fibers and increase the paper mechanical strength. The carbon fiber papers were dried after resin impregnation using a convective oven at 120 °C temperature for 10 min. The hot press machine was heated to 160 °C temperature and the workpieces were pressed for 5 min. Graphitization completed the gas diffusion substrate (GDS) process. GDL involves immersing the paper in a 5% polytetrafluoroethylene (PTFE) solution, coating the paper with a micro porous layer (MPL). This study shows the proposed ultra-thin GDL fabrication method is suitable for PEMFC applications and exhibits feasible functionality for fuel cells.     

Optimal parameter estimation for PEMFC using modified monarch butterfly optimization

The present study develops a new optimization method called monarch butterfly optimization algorithm for optimal parameter estimation of the polymer electrolyte membrane fuel cell (PEMFC). After designing the proposed methodology, it is implemented to 250 MW PEMFC stack under different operating conditions to show the system efficiency and the results are compared with some state-of-the-art methods including Grass Fibrous Root Optimization Algorithm, hybrid Teaching Learning Based Optimization-Differential Evolution Algorithm, and the basic MBO algorithm. Two operational conditions in 3/5 bar and 80°C and 2.5/3 bar, 70°C are used for model verification. The main idea is to minimize the sum of square error (SSE) between the estimated and the actual data. Simulation results in the first condition give an SSE of value 7.277667729 with 9.28434e−16 SD value and in the second condition, an SSE of value 4.52810115 with 0.043581628 standard deviations has been reached as the minimum value among the other compared methods that indicate the accuracy and the robustness of the suggested method toward the analyzed methods. The algorithm also gives a convergence speed of 540 iterations and 370 iterations for conditions 1 and 2, respectively that are the fastest in the study.     

Dynamic water transport and droplet emergence in PEMFC gas diffusion layers

The dynamics of liquid water transport through the gas diffusion layer (GDL) and into a gas flow channel are investigated with an ex situ experimental setup. Liquid water is injected through the bottom surface of the GDL, and the through-plane liquid pressure drop, droplet emergence and droplet detachment are studied. The dynamic behaviour of water transport in and on the surface of the GDL is observed through fluorescence microscopy, and the through-plane liquid pressure drop is measured with a pressure transducer. With an initially dry GDL, the initial breakthrough of liquid water in the GDL is preceded by a substantial growth of liquid water pressure. Post-breakthrough, droplets emerge with a high frequency, until a quasi-equilibrium liquid water pressure is achieved. The droplet emergence/detachment regime is followed by a transition into a slug formation regime. During the slug formation regime, droplets tend to pin near the breakthrough location, and the overall channel water content increases due to pinning and the formation of water slugs. Droplets emerge from the GDL at preferential breakthrough locations; however, these breakthrough locations change intermittently, suggesting a dynamic interconnection of water pathways within the GDL. The experiments are complemented by computational fluid dynamics (CFD) simulations using the volume of fluid method to illustrate the dynamic eruption mechanism.     

Multi-objective optimization of gradient porosity of gas diffusion layer and operation parameters in PEMFC based on recombination optimization compromise strategy

Proton exchange membrane fuel cell (PEMFC) is one of the most promising power energy sources in the world, and its mechanism research has become the main starting point to improve the comprehensive performance of fuel cells. The gas diffusion layer (GDL) of a proton exchange membrane fuel cell has a significant impact on the overall performance of the cell as an important component in supporting the catalytic layer, collecting the current, conducting the gas and discharging the reaction product water. In this paper, a three-dimensional two-phase isothermal fuel cell model is established based on COMSOL, the gradient porosity of the GDL, thickness of the GDL, operating voltage and working pressure of proton exchange membrane fuel cell are analyzed, the consistency problem of fuel cell performance improvement and life extension that is easily overlooked in numerous studies is found. On this basis, a neural network proxy model is constructed through a large amount of data, and a multi-objective genetic optimization algorithm based on the compromise strategy of recombination optimization is proposed to optimize the uniformity of fuel cell power and oxygen molar concentration distribution, which improves the performance of the fuel cell by 1.45% compared with the power increase when it is not optimized. At the same time, the uniformity of oxygen distribution is improved 10.28%, which makes the oxygen distribution more uniform, prolongs the life of the fuel cell, and fills the gap in the optimization direction of the comprehensive performance of the fuel cell.     

Development of a novel hydrophobic/hydrophilic double micro porous layer for use in a cathode gas diffusion layer in PEMFC

In this study, a gas diffusion layer (GDL) was modified to improve the water management ability of a proton exchange membrane fuel cell (PEMFC). We developed a novel hydrophobic/hydrophilic double micro porous layer (MPL) that was coated on a gas diffusion backing layer (GDBL). The water management properties, vapor and water permeability, of the GDL were measured and the performance of single cells was evaluated under two different humidification conditions, R.H. 100% and 50%. The modified GDL, which contained a hydrophilic MPL in the middle of the GDL and a hydrophobic MPL on the surface, performed better than the conventional GDL, which contained only a single hydrophobic MPL, regardless of humidity, where the performance of the single cell was significantly improved under the low humidification condition. The hydrophilic MPL, which was in the middle of the modified GDL, was shown to act as an internal humidifier due to its water absorption ability as assessed by measuring the vapor and water permeability of this layer.     

Facilitating mass transport in gas diffusion layer of PEMFC by fabricating micro-porous layer with dry layer preparation

For a proton exchange membrane fuel cell (PEMFC), dry layer preparation was optimized and applied to fabricate a micro-porous layer (MPL) for a gas diffusion layer (GDL). The MPLs fabricated by dry layer preparation and the conventional wet layer preparation were compared by physical and electrochemical methods. The PEMFC using dry layer MPLs showed better performance than that using wet layer MPLs, especially when the cells were operated under conditions of high oxygen utilization rate and high humidification temperature of air. The mass transport properties of the GDLs with the dry layer MPLs were also better than with the wet layer MPLs, and were found to be related to the pore size distribution in GDLs. The differences in surface morphology and pore size distribution for the GDLs with the dry layer and wet layer MPLs were investigated and analyzed. The dry layer preparation for MPLs was found to be more beneficial for forming meso-pores (pore size in the range of 0.5–15 μm), which are important and advantageous for facilitating gas transport in the GDLs. Moreover, the GDLs with the dry layer MPLs exhibited better electronic conductivity and more stable hydrophobicity than those with the wet layer MPLs. The reproducibility of the dry layer preparation for MPLs was also satisfying.