Mesoporous carbon as Pt support for PEM fuel cell

A mesoporous carbon (MP) supported Pt nanocatalyst was evaluated as anode and cathode catalyst for PEM fuel cell. Kinetics study of the oxygen reduction reaction were characterized by using the rotating disk electrode (RDE) and rotating ring disk electrode (RRDE) techniques in acid media. Membrane electrode assemblies (MEAs) were prepared using Pt supported on MP as anodic and cathodic catalysts and the fuel cell performance evaluated. Polarization and power curves show a similar performance as cathode catalyst when compared to commercial catalyst while there is an 8% improvement when used as anode catalyst.     

PEM fuel cell electrodes

The design of electrodes for polymer electrolyte membrane fuel cells (PEMFC) is a delicate balancing of transport media. Conductance of gas, electrons, and protons must be optimized to provide efficient transport to and from the electrochemical reactions. This is accomplished through careful consideration of the volume of conducting media required by each phase and the distribution of the respective conducting network. In addition, the issue of electrode flooding cannot be neglected in the electrode design process. This review is a survey of recent literature with the objective to identify common components, designs and assembly methods for PEMFC electrodes. We provide an overview of fabrication methods that have been shown to produce effective electrodes and those that we have deemed to have high future potential. The relative performances of the electrodes are characterized to facilitate comparison between design methodologies.     

Performance of novel bimetallic carbonyl clusters as PEM fuel cell anodes,a comparative study

This work describes the performance of novel bimetallic catalysts, prepared from ruthenium, rhodium and iridium carbonyl clusters by a thermolysis procedure in o-dichlorobenzene. The electrochemical characterization by the rotating disk electrode technique in 0.5 mol L⁻¹ H₂SO₄ showed that the Ru_xIr_y(CO)_n, Ru_xRh_y(CO)_n and Rh_xIr_y(CO)_n clusters are able to perform both the hydrogen oxidation reaction (HOR) and oxygen reduction reaction (ORR), even in the presence of fuel cell contaminants such as CO and methanol, respectively. These promising results led us to evaluate the new materials as electrodes in a single fuel cell, using a Fuel Cell Test System designed and built in our group. The performance results of the three bimetallic clusters as anodes in a hydrogen PEM fuel cell are presented in this work. In the tests different H₂ and O₂ gas flows were fed into the cell to determine the most adequate ratio for maximum power. In the absence of CO, the results showed that although the three bimetallic materials had a similar performance to that of platinum with low flows of both reactants, Ru_xIr_y(CO)_n showed the best electrocatalytic parameters. When the hydrogen fuel feed was contaminated with 100 ppm and 0.5% CO, the commercial platinum activity decreased considerably or was completely lost. However, while the current density of the novel materials also decreased in the presence of CO, it was significantly above that of platinum nanoparticles, the Rh_xIr_y(CO)_n and Ru_xIr_y(CO)_n catalysts showing the best performance in the presence of 100 ppm CO and 0.5% CO respectively. These results are promising in the context of PEM fuel cells using reforming hydrogen.     

The influence of ethene impurities in the gas feed of a PEM fuel cell

Hydrogen produced by reforming may contain traces of hydrocarbon contaminants. These traces may affect the performance and lifetime of a fuel cell run on reformate-hydrogen. This study treats the influence of low concentrations of ethene on the adsorption and deactivation chemistry in a polymer electrolyte membrane (PEM) fuel cell. The study employs mainly cyclic voltammetry accompanied with an on-line mass spectrometer to analyse the outlet gas. Results from adsorption and desorption, by either oxidation or reduction, are presented, and the influence of adsorption potential, temperature and humidity and the presence of hydrogen are discussed. The results show that the adsorption of traces of ethene in a fuel cell is highly dependent on adsorption potential and that ethene adsorbs on Pt catalyst in a limited potential window only. Ethene cannot displace adsorbed H and is oxidised already at potentials of 0.6 V versus RHE at 80 °C, where the only detectable product is CO₂. A considerable part of ethene adsorbed at potentials above the hydrogen adsorption/desorption region can be reduced at low potentials and is desorbed as methane or ethene. Overall, the effect of low concentrations of ethene in the hydrogen feed on fuel cell performance is minimal, and no significant loss in cell voltage is found when ethene contaminated hydrogen is fed to a fuel cell running on hydrogen and oxygen at a constant load at 80 °C and at highly humidified conditions.     

Onboard fuel processor for PEM fuel cell vehicles

To lower vehicle greenhouse gas emissions, many automotive companies are exploring fuel cell technologies, which combine hydrogen and oxygen to produce electricity and water. While hydrogen storage and infrastructure remain issues, Renault and Nuvera Fuel Cells are developing an onboard fuel processor, which can convert a variety of fuels into hydrogen to power these fuel cell vehicles.The fuel processor is now small enough and powerful enough for use on a vehicle. The catalysts and heat exchangers occupy 80 l and can be packaged with balance of plant controls components in a 150-l volume designed to fit under the vehicle. Recent systems can operate on gasoline, ethanol, and methanol with fuel inputs up to 200 kWth and hydrogen efficiencies above 77%. The startup time is now less than 4 min to lower the CO in the hydrogen stream to the target value for the fuel cell.     

Constructal PEM fuel cell stack design

This paper describes a structured procedure to optimize the internal structure (relative sizes, spacings), single cells thickness, and external shape (aspect ratios) of a polymer electrolyte membrane fuel cell (PEMFC) stack so that net power is maximized. The constructal design starts from the smallest (elemental) level of a fuel cell stack (the single PEMFC), which is modeled as a unidirectional flow system, proceeding to the pressure drops experienced in the headers and gas channels of the single cells in the stack. The polarization curve, total and net power, and efficiencies are obtained as functions of temperature, pressure, geometry and operating parameters. The optimization is subjected to fixed stack total volume. There are two levels of optimization: (i) the internal structure, which accounts for the relative thicknesses of two reaction and diffusion layers and the membrane space, together with the single cells thickness, and (ii) the external shape, which accounts for the external aspect ratios of the PEMFC stack. The flow components are distributed optimally through the available volume so that the PEMFC stack net power is maximized. Numerical results show that the optimized single cells internal structure and stack external shape are “robust” with respect to changes in stoichiometric ratios, membrane water content, and total stack volume. The optimized internal structure and single cells thickness, and the stack external shape are results of an optimal balance between electrical power output and pumping power required to supply fuel and oxidant to the fuel cell through the stack headers and single-cell gas channels. It is shown that the twice maximized stack net power increases monotonically with total volume raised to the power 3/4, similarly to metabolic rate and body size in animal design.     

Understanding PEM fuel cell dynamics: The reversal curve

In this contribution the reversal line, a new voltage–current (U–i) characteristic curve, is proposed to analyze the transient behavior after an arbitrary load step. The response of a differential polymer electrolyte membrane (PEM) fuel cell to the changes in current, voltage, resistance and power is evaluated, and the existence of the curve is established. Furthermore, the influence of the starting point and the relative humidity is investigated. By using this approach, it is possible to predict the trajectory followed after any load step in the U–i plane and to anticipate infeasible load steps as well as the presence and magnitude of overshoots or undershoots in the cell response.     

The effects of porosity distribution variation on PEM fuel cell performance

Gas diffusion layers (GDL) are one of the important parts of the PEM fuel cell as they serve to transport the reactant gases to the catalyst layer. Porosity of this layer has a large effect on the PEM fuel cell performance. The spatial variation in porosity arises due to two effects: (1) compression of the electrode on the solid landing areas and (2) water produced at the cathode side of gas diffusion layers. Both of these factors change the porosity of gas diffusion layers and affect the fuel cell performance. To implement this performance analysis, a mathematical model which considers oxygen and hydrogen mass fraction in gas diffusion layer and the electrical current density in the catalyst layer, and the fuel cell potentials are investigated. The porosity variation in the GDL is calculated by considering the applied pressure and the amount of the water generated in the cell. The validity of the model is approved by comparing the computed results with experimental data. The obtained results show that the decrease in the average porosity causes the reduction in oxygen consumption, so that a lower electrical current density is generated. It is also shown that when the electrical current density is low, the porosity variation in gas diffusion layer has no significant influence on the level of polarization whereas at higher current density the influence is very significant. The porosity variation causes non-uniformity in the mass transport which in turn reduces the current density and a lower fuel cell performance is obtained.     

Impedance studies on direct methanol fuel cell anodes

The processes taking place in direct methanol fuel cell anodes are characterized by ac impedance spectroscopy. Under conditions of practical interest, i.e., low methanol stoichiometry factors, the kinetic and the mass-transport resistance give rise to two well-resolved semicircles in the Nyquist plot. When mass-transport limitations are excluded, inductive loops occur in the complex plane which are interpreted in terms of the most widely accepted reaction mechanism for methanol electrooxidation. A simple equivalent circuit is used to model this impedance behaviour.     

Development of a cylindrical PEM fuel cell

Proton exchange membrane fuel cells (PEMFCs) have strong potential as power conversion devices of the future, especially for man-portable and mobile applications. However, the manufacturing cost should be significantly reduced for making PEMFCs commercially attractive. An improvement of the power density with respect to the weight of the cell - termed as gravimetric power density in this study - can help in achieving lower manufacturing cost and reducing parasitic power losses, which is particularly important in man-portable applications. Furthermore, the power density of a PEMFC with respect to the overall volume of the cell - termed as volumetric power density in this study - must be improved for man-portable and automotive applications. The bipolar plates made out of graphite contribute significantly to the cost, weight, and volume of the cell. The state-of-the-art PEM fuel cells are of planar design. While several commercial planar prototypes have been demonstrated, cost and water management are still major issues. These problems arise partly as a result of the complicated bipolar plate design in planar PEMFC. Because the planar fuel cell concept has been so well-entrenched, alternate designs have not been seriously pursued. In this paper, we present some experimental studies on a novel cylindrical PEM fuel cell design that addresses the cost, gravimetric and volumetric power density issues. This study while highlighting the advantages of the tubular design also identifies areas of research that will have tremendous utility in further development of this technology.     

Multi-walled carbon nanotubes decorated by platinum catalyst for high temperature PEM fuel cell

In the literature, studies on platinum catalysts deposited on multi-walled carbon nanotube (Pt/MWCNT) have been mostly focused on low temperature fuel cell (LT-PEMFC) applications. In this study, we focus the synthesis and characterization of high temperature fuel cell (HT-PEMFC) performance of Pt/MWCNT in short and long term. The structural properties of the Pt/MWCNT electrocatalyst were analyzed by XRD, TGA, SEM and TEM measurements. The Pt/MWCNTs were also characterized by electrochemical measurements for durability estimation. Laboratory scale MEA with Pt/MWCNT was prepared by ultrasonic coating technique and has been tested in situ in single HT-PEMFC. Performance curves in dry Hydrogen/Air system were obtained that demonstrated performance comparable to commercial catalysts in that HT-PEMFC. The characterizations specified that the electrocatalytic and HT-PEMFC performance of the Pt/MWCNT catalysts are higher power density (0.360 W/cm²) than Pt/C (0.310 W/cm²) at 160 °C. The results obtained show that the synthesized catalysts are suitable for high temperature applications. In addition, the stability studies of MEAs prepared with Pt/MWCNT catalyst were performed by AST tests and compared with Pt/C based MEA.     

Performance study of a PEM fuel cell

This paper presents the installation, maintenance and the efficiency of a Polymer Electrolyte Membrane (PEM) fuel cell, Ballard Trade Mark that use pure hydrogen as fuel and air as an oxidant. A study of the overall efficiency, considering the co-generation of electrical and thermal energies, is performed. The system consists of the cell, a CC/CC converter, a battery, a DC/AC inverter and the load. The behavior of the system is experimentally analyzed for different load states (cases) by measuring and controlling all the parameters registered by the communication software of the cell. The software can adjust limit values for current intensity, hydrogen flow, pressure and the temperature.     

Microcontroller-based emulation of a PEM fuel cell

This paper proposes an accurate and easy-to-implement emulator which is able to track the characteristic curve of a Proton Exchange Membrane Fuel Cell (PEMFC). Such an emulator is based on a low-cost microcontroller , isolated voltage and current sensors. The proposed emulator takes advantages of the flexibility and robustness. The sensed voltage and current provide to the microcontroller the accurate information to compute the output voltage of an actual PEMFC. The obtained voltage is sent to a digital-to-analog converter in order to command the continuous control voltage. The simplified electrochemistry model is presented and validated through simulation and then corroborated via experimentation. The proposed emulator is subjected to two load conditions: fixed load resistor and power electronic converter. The employed power converter is controlled by a variable duty cycle which is adjusted to a value at which the power extracted from the emulator is maximum.     

PEM燃料电池流场形状研究现状

双极板是质子交换膜燃料电池堆的重要部件之一,流场形状结构构成了双极板最主要特征。文章将近年来流场形状的研究现状进行梳理,通过对比分析各种流场设计方法,其对反应物与生成物的分布影响,流场内压力、热量及电流密度分布,流场制造成本等。总结各种流场优缺点,得出燃料电池不同实际应用情况下的最佳流场类型。以此为质子交换膜燃料电池流场的结构设计及研究发展方向提供可行性参考。     

阴极流道分流进气对燃料电池性能影响的实验研究

针对高工作电流密度下,燃料电池内局部水淹导致的传质损失问题,本研究提出了一种阴极流道多进口分流进气方式。实验研究了三种典型分流口位置及分流进量对电池性能的影响。研究发现随着分流口远离阴极主进气口,电池性能呈现先上升后下降的趋势,且当分流口靠近主进气口时,增加分流量有助于电池性能提升,但分流量的增加对电池性能的提升存在一个极限值;因此,在对电池进行分流进气优化时需综合考虑分流口位置和分流量的影响。当分流口为SIP-30%且分流量为按化学当量比ξc = 0.75取值时,分流进气方式相比传统进气方式,电池的最大功率密度高出17.8%。