质子交换膜燃料电池研究进展

由于质子交换膜燃料电池（PEMFC）具有能量转化效率高、寿命长、比功率和比能量高、以及对环境友好等优点,近年来得到迅速发展.笔者综述了PEMFC的特点,分析了PEMFC在国内外的最新研究进展,介绍了PEMFC的应用前景,并指出了PEMFC研究当前需要解决的技术问题及其发展趋势.     

以新型渐缩式流道增进质子交换膜燃料电池性能

Based on use of multi-dimensional models, this investigation simulates the performance of a proton exchange membrane fuel cell by varying the channel pattern. In the one-dimensional model, the porosity of the gas diffusion layer is 0.3. The model reveals the water vapor distribution of the fuel cell and demonstrates that the amount of water vapor increases linearly with the reduction reaction adjacent to the gas channel and the gas diffusion layer. Secondly, four novel tapered gas channels are simulated by a two-dimensional model. The model considers the distributions of oxygen, the pressure drop, the amount of water vapor distribution and the polarization curves. The results indicate that as the channel depth decreases, the oxygen in the tapered gas channel can be accelerated and forced into the gas diffusion layer to improve the cell performance. The three-dimensional model is employed to simulate the phenomenon associated with four novel tapered gas channels. The results also show that the best performance is realized in the least tapered gas channel. Finally, an experimentally determined mechanism is found to be consistent with the results of the simulation.     

质子交换膜燃料电池研究及应用现状

介绍了国内外质子交换膜燃料电池(PEMFC)研究的整体现状及水平,分别讨论了PEMFC的3个关键部件:质子交换膜的材料要求,电化学反应催化剂的特点,膜电极的组成、制备工艺和最新进展,重点讨论了全氟磺酸型质子交换膜的类型、优缺点和当前的研究方向。在此基础上,追述了近年来国内外以PEMFC作为电动汽车动力源的实际应用情况,并指出应用PEMFC存在的问题。可以看到,PEMFC具有广阔的应用前景,将会在电动汽车方面得到最早的商业化应用。     

燃料电池用碱性膜材料的研究进展

碱性膜直接甲醇燃料电池因为结合了质子交换膜燃料电池和液体碱燃料电池的优点而产生自身独特的性质,使其可以在一定程度上弥补质子交换膜燃料电池以及液体碱燃料电池的缺点而尤其引人关注。其中碱性膜电解质为碱性膜燃料电池的核心组件,其性能直接关系到燃料电池的性能及寿命。截至目前,关于碱性膜材料的制备及应用方面的报道较多,涉及的碱性膜电解质的种类也较多。本文以燃料电池用碱性膜电解质为综述内容,对国内外关于碱性膜电解质的研究报道进行系统的梳理和介绍。     

Effect of gas diffusion layer compression on the performance in a proton exchange membrane fuel cell

This study investigates the gas permeability, bulk density, thickness and conductivity of two types of gas diffusion layer (OC14, NC14) as a function of the compressed thickness. The compression of a gas diffusion layer reduces gas permeability and contact resistance. The performance is measured using a single proton exchange membrane fuel cell (PEMFC) with an active area of 25 cm². The results provide an optimum value of compression ratio that maximizes the cell performance. For OC14 the optimum compression ratio is about 64%, whereas for NC14 it is 59%. The best performances are 375 mA/cm² and 296 mA/cm² at 0.7 V, respectively. These results concerning the balance between compression and performance provide vital information for the fabrication of stacks and support for industrial applications.     

Prediction of methanol and water fluxes through a direct methanol fuel cell polymer electrolyte membrane

Development of a direct methanol fuel cell (DMFC) mass flux model, using conventional transport theory, is presented and used to predict the fluid phase superficial velocity, methanol and water molar fluxes, and the chemical species (methanol and water) dimensionless concentration profiles in the polymer electrolyte membrane, Nafion^® 117, of a DMFC. Implementation of these equations is illustrated to generate the numerical data as functions of the variables such as the pressure difference across the membrane, methanol concentration at the cell anode, temperature, and position in the membrane.     

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.     

Steady-state operation of a compressor for a proton exchange membrane fuel cell system

The performance of a system consisting of a proton exchange membrane (PEM) fuel cell coupled to a centrifugal air compressor is simulated. Two modes of operation of the system are investigated: one in which the speed of the compressor is constant, and the other in which the compressor speed is varied with the electric load on the fuel cell stack. The operating characteristics of the compressor and the PEM fuel cell stack and their influence on the system efficiency are analyzed for a step change in the stack current. The effects of the fuel cell stack back-pressure and the electric load on the compressor power consumption and the system efficiency are studied. It is found that the system efficiency is higher when the fuel cell stack is operated at a constant oxygen gas stoichiometry by varying the compressor speed instead of at a constant compressor speed. The system model can be used to determine the rotation speed of the compressor for various electric loads.     

质子交换膜燃料电池强化传质

传质问题制约着燃料电池性能的提高。通过理论分析、Fluent模拟,针对质子交换膜燃料电池流道中加凸台和电极扩散层开孔两种方法,分别研究其对强化电池内部传质的效果。结果表明,上述两种方式均能有效强化电池内部传质,提高电池性能。但是加凸台增加了风机的寄生功率,综合性能提升不显著。     

中压氢-氧质子交换膜燃料电池的运行特性

通过设计阴极流道宽度为1 mm与2 mm的单电池,研究了不同温度下闭口中压氢-氧质子交换膜燃料电池的运行特性。结果表明：(1)2 mm的电池有较好的闭口稳定运行特性,在800 mA·cm-2下,1 mm的电池闭口运行时,大约经过3 min,电压从0.7 V下降到0.5V,而2 mm的流场结构能实现电池53 min的运行;(2)电池性能随温度的升高而下降,相对于65℃运行,温度为80℃时,1mm的电池闭口运行时,大约经过1.7 min,电压从0.69 V下降到0.5 V,此时为维持电池的高性能运行,氧气侧所需的排放时间越短;(3)电池的内阻随温度的升高而增大,高温时增幅较小。     

Computational fluid dynamics simulation of polymer electrolyte membrane fuel cells operating on reformate

Carbon monoxide (CO) can extremely diminish the polymer electrolyte membrane fuel cell (PEMFC) performance since it is preferentially absorbed on the platinum catalyst layer blocking and reducing the number of catalyst sites available for the hydrogen oxidation reaction. To gain a good insight of CO poisoning characteristics so as to provide a remedial solution for CO-poisoned PEMFCs, a two-dimensional, isothermal, and single phase CO poisoning numerical model taking into account the transport phenomena, electrochemical reactions and multi-component gas mixture transport is developed for such purpose. Linear and bridged-bonded adsorbed CO modes were considered to occur in parallel on the highly dispersed nano-crystalline Pt/C and PtRu/C catalysts. By performing computational fluid dynamics numerical simulations, this study clearly demonstrates the CO poisoning mechanisms and characteristics of PEMFCs. The numerical results obtained are in reasonably good agreement with the experimental data showing the predictive capability of the model.     

质子交换膜燃料电池膜中气态水管理模型

分析质子交换膜燃料电池的膜水含量与运行参数的关系,从工程方法的角度建立水传输模型.模型分析得到,要提高膜的水合程度,需要通过增湿反应气体.过高的增湿反应气体又会引起阴极扩散层水的泛滥,需通过调节反应气体流量来缓解水的泛滥.为保证膜的高水合程度和低的阴极扩散层水的泛滥,建立了膜水含量的神经网络控制模型,为电池水管理奠定了基础.     

质子交换膜燃料电池仿真模型研究进展

质子交换膜燃料电池具有高效清洁等优势,是一种潜力巨大的绿色能源技术。数学模型作为一种合理可靠的工具,通过模拟电池内部的电化学传热传质过程,研究运行参数和结构参数对电池性能和寿命的影响,可以指导电池的优化设计。本文综述了近年来燃料电池催化层、气体扩散层和流道的研究模型,整理了各部件建模的影响因素和优化方法,以期对燃料电池建模以及电池各部件的优化设计起到参考作用。文中指出,考虑到现在仿真存在的局限性,未来主要研究方向为燃料电池系统研究与机理模型的结合、催化层微观结构的建模、非贵金属催化剂建模、气体扩散层衰减模型研究、大面积流道模型、三维模型温度分布研究以及全尺寸质子交换膜燃料电池模型的开发。     

Modelling and experimental validation of a high temperature polymer electrolyte fuel cell

A steady-state, isothermal, one dimensional model of a proton exchange membrane fuel cell (PEMFC), with a polybenzimidazole (PBI) membrane, was developed. The electrode kinetics were represented by the Butler–Volmer equation, mass transport was described by the multi-component Stefan–Maxwell equations and Darcy’s law and the ionic and electronic resistances described by Ohm’s law. The model incorporated the effects of temperature and pressure on the open circuit potential, the exchange current density and diffusion coefficients, together with the effect of water transport across the membrane on the conductivity of the PBI membrane. The polarisation curves predicted by the model were validated against experimental data for a PEMFC operating in the temperature range of 125–200 °C. There was good agreement between experimental and model data of the effect of temperature and oxygen/air pressure on cell performance. The model was used to simulate the effect of catalyst loading and the Pt/carbon ratio on cell performance and, in the latter case, a 40 wt.% Pt/C ratio gave the highest peak power density.     

Spreading of liquid droplets on proton exchange membrane of a direct alcohol fuel cell

Spreading of liquid droplets over solid surfaces is a fundamental process with a number of applications including electro-chemical reactions on catalyst surface in membrane electrode assembly of proton exchange membrane (PEM) fuel cell and direct alcohol fuel cell. The spreading process of droplet on the PEM porous substrate consists of two phenomena, e.g., spreading of droplet on PEM surface and imbibition of droplet into PEM porous substrate. The shrinkage of the droplet base occurs due to the suction of the liquid from the droplet into the PEM porous substrate. As a result of these two competing processes, the radius of the drop base goes through a maximum with time. The variation of droplet base and front diameter with time on the PEM porous substrate is monitored using microscope fitted with CCD camera and a PC. It is seen that the droplet base diameter goes through a maximum with time, whereas the front diameter increases continuously with time. Further, methanol droplet spreading and wetting front movement was faster than that for ethanol and deionized water. As the PEM porous substrate is wetted and imbibed well by the methanol compared to ethanol, it is expected that the cross over of methanol would be higher than that of ethanol in direct alcohol fuel cell. It should be noted that cross over of alcohol from anode side to cathode side through membrane is detrimental to the fuel cell operation. The experimental data on the variation of droplet base and wetting front diameter with time is predicted by the model available in the literature.     

质子交换膜燃料电池动态过程的数值模拟

为描述质子交换膜燃料电池的动态过程,发展了一个基于计算流体动力学的非稳态、非等温的三维两相流数学模型.应用模型对一蛇形流道结构的质子交换膜燃料电池单体进行了数值计算,得到了电池启动过程中电池阴极侧膜表面温度和电流密度等特征参数的动态过程变化曲线.最后,分析了阴极入口速度、湿度和电池电压阶跃变化后电池特性的动态响应特性.结果表明：电池的启动时间和阶跃响应时间均为秒的数量级,与大多数模型模拟的结果相一致.     

An empirical fuel cell polarization curve fitting equation for small current densities and no-load operation

A logarithmic term is applied to account for the charge transfer overvoltage with most empirical polarization curve fitting equations for polymer electrolyte membrane fuel cells. The logarithmic term applied with state-of-the-art fitting equations is proportional to the logarithm of the cell output current density. This provides good fitting characteristics with large current densities, but results in significant deviations from measured current/voltage characteristics if small current densities or no-load operation are investigated. A modified logarithmic charge transfer overvoltage term utilising the exchange current density and an internal cell current density is therefore introduced to provide accurate fitting characteristics with small current densities and no-load operation. Fitting characteristics of this modified polarization curve fitting equation are investigated and compared to standard fitting equations.     

High temperature proton exchange membrane fuel cell using a sulfonated membrane obtained via H2SO4 treatment of PEEK-WC

A method for the sulfonation of PEEK-WC, a glassy poly(ether ether ketone) with sulphuric acid is presented. Depending on the reaction time, polymers with ion exchange capacity (IEC) from 0.30 to 0.76 meq_H⁺/g are obtained, as determined by titration with NaOH solutions. The thermal properties of the polymers were studied by differential scanning calorimetry, showing that the glass transition temperature increases with increasing degree of sulfonation, from 224 °C for pure PEEK-WC to 246 °C for the polymer having an IEC of 0.76 meq_H⁺/g. The sulfonated polymers were used to prepare proton exchange membranes for possible application in fuel cells. Dense membranes were prepared by solvent evaporation, using DMA as the solvent. The transport properties of the membranes were determined in terms of water uptake and permeability for hydrogen and oxygen. Electrochemical characterization was performed by measuring cell voltage and power density curves as a function of current density at different working temperatures and the results were compared with those of a commercial Nafion membrane. A power density of 284 mW/cm² was obtained for S-PEEK-WC membrane at 120 °C in H₂/air fuel cell, slightly above the corresponding value found for Nafion.     

Trends for fuel cell membrane development

Fuel cells are considered a promising energy conversion technology of the future owing to inherent advantages of electrochemical conversion over thermal combustion processes. In the polymer electrolyte fuel cell (PEFC) a proton-conducting polymer membrane is utilized as solid electrolyte, having to allow the transport of protons from anode to cathode yet block the passage of reactants (e.g. H₂, O₂) and electrons. Although PEFC technology has matured substantially over the past two decades, technological barriers, such as insufficient durability and high cost, still delay commercialization in many applications. In this contribution, we review current fuel cell membrane technology and outline approaches that are taken to improve the functionality as well as the chemical and mechanical stability of proton conducting polymers in fuel cells.     

质子交换膜燃料电池可视化研究进展

质子交换膜燃料电池(包括氢氧质子交换膜燃料电池和直接甲醇燃料电池)内的两相流动以及相应的水管理、气管理对燃料电池的性能和寿命有很大的影响,而可视化方法是研究流场槽道内两相流动非常重要的方法之一。可视化实验可以真实地展示气泡或液滴在流场槽道内的生成以及发展过程,有利于了解其进化机制,从而进一步优化气管理、水管理并提高电池性能。本文主要综述了质子交换膜燃料电池两极流场内两相流动的可视化研究进展,讨论了扩散层的润湿性以及扩散层内水的传递机理,还介绍了实现可视化的方法,并提出了可视化研究的不足及发展方向。