Forecast of Performance Parameters of Automotive Fuel Cell Systems – Delphi Study Results

Fuel cells are a promising propulsion technology option in sustainable and zero‐emission drivetrain strategies as they offer a high potential to significantly reduce well‐to‐wheel greenhouse gas emissions and the dependency on fossil energy resources. At the same time, the current technological performance of automotive fuel cell systems is not yet sufficient to meet market demands. Therefore, the technical development of fuel cells is a critical factor for a successful market introduction of fuel cell electric vehicles (FCEV). This paper describes the methodology and results of a two‐round Delphi Survey conducted by the Institut für Kraftfahrzeuge of RWTH Aachen University to assess the technological potential of polymer electrolyte membrane fuel cell (PEMFC) systems in automotive applications by 2030. The analysis of the current and future performance level of key performance indicators (KPI) of automotive fuel cell systems helps to identify critical performance parameters and to prioritize research and development demands. KPI analyzed in the Delphi Survey as forecast parameters include system efficiency, durability, power density, and specific power.     

高温质子交换膜燃料电池用离子液体聚合物电解质的研究进展

综述了近十几年来高温质子交换膜燃料电池用离子液体聚合物电解质的研究进展及其在高温质子交换膜燃料电池中的应用进展,指出了此类电解质目前存在的亟待解决的两个问题：咪唑类离子液体毒化Pt基催化剂和复合膜中离子液体的长期稳定性。最后对高温质子交换膜燃料电池用离子液体聚合物电解质的发展前景作了展望,即开发与Pt基催化剂相容的离子液体聚合物电解质以及预防复合膜内离子液体的流失,即提高高温质子交换膜燃料电池的性能及长期稳定性,最终提高高温燃料电池的寿命。     

Proton-conducting polymer electrolyte membranes based on hydrocarbon polymers

This paper presents an overview of the synthesis, chemical and electrochemical properties, and polymer electrolyte fuel cell applications of new proton-conducting polymer electrolyte membranes based on hydrocarbon polymers. Due to their chemical stability, high degree of proton conductivity, and remarkable mechanical properties, perfluorinated polymer electrolytes such as Nafion^®, Aciplex^®, Flemion^®, and Dow membranes are some of the most promising electrolyte membranes for polymer electrolyte fuel cells. A number of reviews on the synthesis, electrochemical properties, and fuel cell applications of perfluorinated polymer electrolytes have also appeared during this period. While perfluorinated polymer electrolytes have satisfactory properties for a successful fuel cell electrolyte membrane, the major drawbacks to large-scale commercial use involve cost and low proton-conductivities at high temperatures and low humidities. Presently, one of the most promising ways to obtain high performance proton-conducting polymer electrolyte membranes is the use of hydrocarbon polymers for the polymer backbone. The present review attempts for the first time to summarize the synthesis, chemical and electrochemical properties, and fuel cell applications of new proton-conducting polymer electrolytes based on hydrocarbon polymers that have been made during the past decade.     

用于高温质子交换膜燃料电池的聚合物电解质膜研究进展

高温质子交换膜燃料电池在降低燃料电池水热管理复杂性、催化剂中毒方面有明显优势;可改善电池阴阳两极尤其是阴极氧气还原反应的动力学特性,提高电池的效率。聚合物电解质膜作为关键材料之一,在高温时易失水导致质子传导率降低、机械强度和热稳定性不高等问题。本文基于磺酸、磷酸和离子液体等不同质子传递介质,对高温聚合物电解质膜进行综述,比较了各类聚合物电解质膜的优缺点及应用时存在的问题,着重探讨嵌段共聚物在高温聚合物电解质膜方面的潜在应用,指出离子液体的添加不但可作为质子载体,而且在构建嵌段聚合物结构方面可发挥"诱导剂"作用。提出通过分子设计可更好了解嵌段聚合物的空间构效关系,进而通过结构设计提高膜的质子传导性能和稳定性。     

重整甲醇高温聚合物电解质膜燃料电池研究进展与展望

甲醇作为一种安全便捷的液态储氢燃料,具有高含氢量以及高体积能量密度,可经重整为富氢气后与燃料电池系统集成为重整甲醇高温聚合物电解质膜燃料电池,从而高效地将甲醇和氧气的化学能转变为电能。本文针对重整甲醇高温聚合物电解质膜燃料电池的不同类型（外置重整型和内置重整型）,分别对其系统集成的实现与发展进行了总结,并介绍了其现阶段在军用和民用方面的应用情况,同时指出了技术研究与应用存在的瓶颈,并对未来的研究方向进行了展望。未来提升重整甲醇高温聚合物电解质膜燃料电池性能的努力在于开发低温工作的高效甲醇重整催化剂,以及高温稳定运行的聚合物电解质膜和非贵金属材料等燃料电池关键材料。     

直接涂膜技术用于质子交换膜燃料电池膜电极制备

引　言质子交换膜燃料电池 (PEMFC)是极具吸引力的电化学能量转换装置 ,是未来电动汽车的主要动力源 ,也是洁净高效的新型化学电源 .对于电动汽车的应用 ,要求PEMFC提供高能量密度、低催化剂负载量 ,以降低系统体积和成本[1] .膜电极(membraneandelectrodeassembly ,简称MEA)是由聚合物电解质膜、电极催化剂和扩散层材料组合而成的三明治式结构组件 ,类似于计算机的芯片 ,是燃料电池的核心部件 ,长期以来大量的研究集中于MEA新材料设计与制备 ,以提高电池的性能 .近年来 ,对MEA的微观结构分析、MEA制备工艺与电池性能的关系研究工作明显增多[2～ 7] .从PEM FC研究实践中发现 ,如何减少电极中Pt催化剂负载量并能继续保持或者提高电池性能的MEA制备技术开发至关重要 .其中超薄Pt层沉积法[8～ 10 ] 是MEA的制备新技术之一 .与传统的基于墨水涂布(based inkprinting)的方法相比 ,喷溅沉积法(sputterdeposit) [9] 制备的MEA提高了电池的性能和催化剂的利用率 ,它是用直接喷溅沉积法 (directlydeposit) [10...     

Performance of a direct methanol fuel cell

The performance of a direct methanol fuel cell based on a Nafion® solid polymer electrolyte membrane (SPE) is reported. The fuel cell utilizes a vaporized aqueous methanol fuel at a porous Pt–Ru–carbon catalyst anode. The effect of oxygen pressure, methanol/water vapour temperature and methanol concentration on the cell voltage and power output is described. A problem with the operation of the fuel cell with Nafion® proton conducting membranes is that of methanol crossover from the anode to the cathode through the polymer membrane. This causes a mixed potential at the cathode, can result in cathode flooding and represents a loss in fuel efficiency. To evaluate cell performance mathematical models are developed to predict the cell voltage, current density response of the fuel cell.     

A thin-film/agglomerate model of a proton-exchange-membrane fuel cell cathode catalyst layer with consideration of solid-polymer-electrolyte distribution

A thin-film/agglomerate model for the cathode part of a proton-exchange-membrane fuel cell is developed. Parameter estimation is employed to determine the exchange current density in the catalyst layer, proton conductivity of the recast ionomer, and oxygen diffusivity in the solid polymer electrolyte. The effects of catalyst and polymer electrolyte loadings in the catalyst layer on the cell performance are demonstrated using this model. The influence of polymer electrolyte distribution in the catalyst layer is correlated with the oxygen diffusion and proton migration rates within the electrolyte. It is found that proton migration in the polymer electrolyte is the dominant factor for cell current density under normal operating conditions. A better cell performance is achieved by a concentrated polymer electrolyte near the catalyst layer/membrane interface.     

Polymer electrolyte membrane modification in direct ethanol fuel cells: An update

Direct ethanol fuel cells (DEFCs) offer a high degree of design flexibility, ranging from a single cell to a massive multi-cell that can be used in various applications, including portable devices, transportation, and stationary applications. Unfortunately, the most significant barrier to the commercialization of DEFCs is getting low-cost and ethanol permeability, high conductivity performance, and extended durability of polymer electrolyte membranes, as key components that highly influence the overall performance. In this paper, the recent progress in developing the polymer electrolyte membrane for the application of DEFCs has been comprehensively reviewed. Focusing on an updated modification of polymeric materials in the last 5 years, including Nafion-based membrane, polyvinyl alcohol-based membrane, polybenzimidazoles-based membrane, chitosan-based membrane, and sodium alginate-based membrane, as well as factors and challenges that affected the performance of polymer electrolyte membranes have been discussed, including the main characterization, catalyst selection, cell design, and work in membrane and cell performance of DEFCs. All discussion addresses the strategy to improve the performance of polymer electrolyte membranes in DEFCs in order to penetrate the commercialization stages.     

Comparing Anode Gas Recirculation with Hydrogen Purge and Bleed in a Novel PEMFC Laboratory Test Cell Configuration

In automotive‐type polymer electrolyte membrane fuel cell (PEMFC) systems, impurities and inert gases accumulate in the anode gas recirculation loop. Therefore, the impurity limits, dictated by the current hydrogen fuel specification (ISO 14687‐2:2012), also require quantification with representative fuel cell test systems applying anode gas recirculation, that enables high fuel utilization rates and accumulation of impurities.We report a novel PEMFC laboratory test cell configuration mimicking automotive conditions. This setup enabled comparison of two operation modes, hydrogen bleed and purge, within 84.4%–98.6% fuel utilizations. The results indicate that similar enrichment dynamics apply to both bleed and purge modes.The configuration employed a membrane dryer to circumvent the 60 °C limit of commercially available recirculation pumps. The membrane dryer allows heat and humidity extraction from the anode exit gas stream, enabling the adoption of conventional recirculation pumps, minimizing water condensation, and making sampling with on‐line gas analysis instruments easier. The results show that anode gas recirculation systems with hydrogen bleed can be implemented in conventional test stations by resorting to commercially available recirculation pumps. This enables realistic and cost‐effective determination of impurity effects for fuel cell system development and new hydrogen fuel standards.     

Alternatives toward proton conductive anhydrous membranes for fuel cells: Heterocyclic protogenic solvents comprising polymer electrolytes

Fuel cells are gaining increasing attention as a clean and promising technology for energy conversion. One of the key benefits of fuel cells compared to other methods is the direct energy conversion that enables the achievement of high efficiency. The electrolyte membrane is the most essential parts of a fuel cell unit, and consequently has been the subject of considerable research and development. Among the various types of proton conducting electrolytes examined for fuel cell applications, polymer electrolyte membranes (PEMs) are regarded as viable candidates since they enable operation of the cells at desirably low temperatures. This review describes recent progress in the design and development of high performance proton conducting PEMs, including the analysis of the design requirements and strategies for development of advanced PEMs for operation in anhydrous conditions. Some of the most widely used types of azole heterocycles are introduced and compared, particularly in terms of their performance characteristics in polyacids containing different functional groups. In addition, the latest research studies and progress in the field of azole-containing and azole-functionalized electrolyte systems are discussed and reviewed.     

聚醚砜-聚乙烯吡咯烷酮高温聚合物电解质膜及燃料电池堆性能研究

基于磷酸掺杂聚苯并咪唑膜（PA/PBI）的高温聚合物电解质膜燃料电池具有高的输出功率和优异的稳定性,然而PBI膜昂贵的价格和复杂的制备工艺限制了高温聚合物电解质膜燃料电池的商业化应用。本研究以成本低和制备工艺简单的聚醚砜-聚乙烯吡咯烷酮（PES-PVP）膜的商业化应用为目标,小规模制备了幅宽为40 cm的PES-PVP复合膜,证实了流延法放大制备PES-PVP复合膜的可行性。PES-PVP膜中每个PVP重复单元的吸附量达4.9个磷酸（PA）分子,且在180℃的质子电导率达85 mS·cm^-1。此外,尺寸为165 cm²的PA/PES-PVP高温膜电极在150℃的输出功率达0.19 W·cm^-2@0.6 V,与同尺寸的商业化PA/PBI高温膜电极的输出功率相当,并在近3000 h的寿命测试中展示出良好的稳定性。最后,将PA/PES-PVP高温膜电极（单片有效面积200 cm²）组装高温膜燃料电池短堆,其中基于3片膜电极的短堆展现出良好的电堆启停稳定性;基于20片膜电极电堆的峰值功率达1.15 kW。以上结果表明所制备的PA/PES-PVP是一种性能优良、价格便宜的高温聚合物电解质膜材料,并且基于该膜材料组装的高温聚合物电解质膜电池和电堆性能优异。本研究工作为高温聚合物电解质膜燃料电池关键材料和电堆的国产化提供了研究基础。     

Effect of ambient conditions on performance and current distribution of a polymer electrolyte membrane fuel cell

The performance and current distribution of a free-breathing polymer electrolyte membrane fuel cell (PEMFC) was studied experimentally in a climate chamber, in which temperature and relative humidity were controlled. The performance was studied by simulating ambient conditions in the temperature range 10 to 40 °C. The current distribution was measured with a segmented current collector. The results indicated that the operating conditions have a significant effect on the performance of the fuel cell. It was observed that a temperature gradient between the fuel cell and air is needed to achieve efficient oxygen transport to the electrode. Furthermore, varying the air humidity resulted in major changes in the mass diffusion overpotential at higher temperatures.     

Application of Gas Permeation in Fuel Cell Powered Vehicles

Main motivation for the use of a polymer electrolyte membrane fuel cell (PEMFC) in traffic applications is its significant higher vehicle efficiency compared to internal combustion engines (ICE) especially under low‐load operation. Hydrogen is the ideal fuel for PEMFCs as it yields the highest level of fuel cell performance. Three different applications for gas permeation inside a fuel cell system have been investigated: water recovery, hydrogen purification, and oxygen enrichment. The focus was on the analysis of the technical feasibility and the availability of capable membranes on the pilot‐scale size for each application.     

Low stress creep response of PTFE sealants applied to PEM fuel cells

Viscoelastic properties of polytetrafluoroethylene (PTFE) play a crucial role in forecasting its long-term behavior in engineering applications. An attempt is made to explore the viscoelastic properties of PTFE sealants that are utilized in polymer electrolyte membrane fuel cell (PEMFC). It is to be noted that PTFE sealants are vulnerable to creep under constant loading at elevated temperatures. Moreover, the creep of sealants will lead to leakage of reactants from the cell, which affects the performance of PEMFC. PTFE is an excellent choice as a sealant material in low-temperature polymer electrolyte membrane fuel cell (LT-PEMFC), which operates in the temperature range of 60–80°C. PTFE can be prominently used as sealants in high-temperature polymer electrolyte membrane fuel cell (HT-PEMFC), as it possesses no significant change in its physical properties within the temperature range of −150 to 300°C along with the working conditions of HT-PEMFC. In LT-PEMFC, the sealants will typically be subjected to low stresses in the range of 1–5 MPa. In this article, the creep response of PTFE sealant material is extensively studied at various temperatures of 25 (room temperature), 35, 45, 55, and 65°C and at three stress levels of 2, 3, and 4 MPa. The time–temperature superposition principle is utilized to develop master curve at a reference temperature of 25°C, to forecast long-term creep characteristics of PTFE sealants. Moreover, the master curve for creep compliance is developed for 4.5 h.     

Characteristics of membrane humidifiers for polymer electrolyte membrane fuel cells

Water management plays an important role in obtaining high performance from a polymer electrolyte membrane fuel cell (PEMFC). To reduce the volume and energy consumption of widely-used bubble humidifiers, membrane humidifiers were fabricated by using an ultrafiltration (UF) membrane and Nafion membranes. The performance of the membrane humidifiers was examined as a function of gas flow rate and operating temperature. A single cell was operated using the UF membrane humidifiers exhibiting almost the same performance with that employing bubble humidifiers.     

On the modeling of water transport in polymer electrolyte membrane fuel cells

Water management is a critical issue in polymer electrolyte membrane (PEM) fuel cells, and water transport through the membrane, catalyst layer and gas diffusion layer has significant impact on the cell performance and durability. In this study, the mechanism of water transport processes in PEM fuel cells has been analyzed through 3-D unsteady non-isothermal simulations, along with a comprehensive examination of various modeling approaches in literature. It is shown that the finite rates of sorption/desorption of water in membrane affect the cell current output and the cell response time. Water dissolved in the membrane should be taken as the proper mechanism of water formation in the cathode of practical PEM fuel cells. Capillary pressure and relative permeability have significant impact on the distribution of liquid water saturation and transport, implying a need for their determination under specific PEM fuel cell conditions.     

Cost effective cation exchange membranes: A review

This paper will look at developments of new polymer electrolyte membranes to replace high cost ion exchange membranes such as Nafion^®, Flemion^® and Aciplex^®. These perfluorinated polymer electrolytes are currently the most commercially utilized electrolyte membranes for polymer electrolyte fuel cells, with high chemical stability, proton conductivity and strong mechanical properties. While perfluorinated polymer electrolytes have satisfactory properties for fuel cell applications, they limit commercial use due to significant high costs as well as reduced performance at high temperatures and low humidity. A promising alternative to obtain high performance proton-conducting polymer electrolyte membranes is through the use of hydrocarbon polymers. The need for inexpensive and efficient materials with high thermal and chemical stability, high ionic conductivity, miscibility with other polymers, and good mechanical strength is reviewed in this paper. Though it is difficult to evaluate the true cost of a product based on preliminary research, this paper will examine several of the more promising materials available as low cost alternatives to ion exchange membranes. These alternative membranes represent a new generation of cost effective electrolytes that can be used in various ion exchange systems. This review will cover recent and significant patents regarding low cost polymer electrolytes suitable for ion exchange membrane applications. Promising candidates for commercial applications will be discussed and the future prospects of cost effective membranes will be presented.     

A Study of Polymer Electrolyte Fuel Cells by the Measurement of AC Impedance,Current Interrupt,and Dew Points: 2. Effect of Cell Temperature

The effect of cell temperature on the performance of a polymer electrolyte fuel cell was examined in the present study. Measurements using the current interrupt and AC impedance methods showed that membrane resistance increased as the cell temperature was reduced. The charge transfer resistance, determined by the AC impedance method, also increased with decreasing cell temperature. The results of electrochemical analysis showed that the temperature of the cell strongly affected the performance of the membrane–electrode assembly in the cell. In addition, the water balance calculated from dew points of fuel gases changed with cell temperature. At a cell temperature of 80 °C, ca. 80% of the water generated on the cathode passed through the membrane to the anode, while at a cell temperature of 40 °C, only ca. 20% of the water on the cathode passed through the membrane to the anode.     

Synthesis and Characterization of a New Fluorine‐Containing Polybenzimidazole (PBI) for Proton‐Conducting Membranes in Fuel Cells

A new type of fluorine‐containing polybenzimidazole, namely poly(2,2′‐(2,2′‐bis(trifluoromethyl)‐4,4′‐biphenylene)‐5,5′‐bibenzimidazole) (BTBP‐PBI), was developed as a candidate for proton‐conducting membranes in fuel cells. Polymerization conditions were experimentally investigated to achieve high molecular weight polymers with an inherent viscosity (IV) up to 1.60 dl g^–1. The introduction of the highly twisted 2,2′‐disubstituted biphenyl moiety into the polymer backbone suppressed the polymer chain packing efficiency and improved polymer solubility in certain polar organic solvents. The polymer also exhibited excellent thermal and oxidative stability. Phosphoric acid (PA)‐doped BTBP‐PBI membranes were prepared by the conventional acid imbibing procedure and their corresponding properties such as mechanical properties and proton conductivity were carefully studied. The maximum membrane proton conductivity was approximately 0.02 S cm^–1 at 180 °C with a PA doping level of 7.08 PA/RU. The fuel cell performance of BTBP‐PBI membranes was also evaluated in membrane electrode assemblies (MEA) in single cells at elevated temperatures. The testing results showed reliable performance at 180 °C and confirmed the material as a candidate for high‐temperature polymer electrolyte membrane fuel cell (PEMFC) applications.