Status and Promise of Fuel Cell Technology

The niche or early entry market penetration by ONSI and its phosphoric acid fuel cell technology has proven that fuel cells are reliable and suitable for premium power and other opportunity fuel niche market applications. Now, new fuel cell technologies – solid oxide fuel cells, molten carbonate fuel cells, and polymer electrolyte fuel cells – are being developed for near‐term distributed generation shortly after 2003. Some of the evolving fuel cell systems are incorporating gas turbines in hybrid configurations. The combination of the gas turbine with the fuel cell promises to lower system costs and increase efficiency to enhance market penetration. Market estimates indicate that significant early entry markets exist to sustain the initially high cost of some distributed generation technologies. However, distributed generation technologies must have low introductory first cost, low installation cost, and high system reliability to be viable options in competitive commercial and industrial markets. In the long‐term, solid state fuel cell technology with stack costs under $100/kilowatt (kW) promises deeper and wider market penetration in a range of applications including a residential, auxillary power, and the mature distributed generation markets. The Solid State Energy Conversion Alliance (SECA) with its vision for fuel cells in 2010 was recently formed to commercialize solid state fuel cells and realize the full potential of the fuel cell technology. Ultimately, the SECA concept could lead to megawatt‐size fuel‐cell systems for commercial and industrial applications and Vision 21 fuel cell turbine hybrid energy plants in 2015.     

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.     

Polymerelektrolytmembranen für Hoch‐ und Niedertemperatur‐Brennstoffzellen aus strahlungsinduzierter Pfropfcopolymerisation

Radiation‐induced graft copolymerization of hydroxyethyl methacrylate with hydroxyethyl acrylate, acrylic acid or glycidyl methacrylate on ethylene tetrafluoroethylene (ETFE) films allow for tailor‐made synthesis of membranes for high and low temperature fuel cell applications. According to the operating temperatures proton conductivity may be achieved via doping with phosphoric acid or a two‐step sulfonation of the functional monomers. Fuel cell tests provide power densities and internal resistances, which indicate that the membranes are suitable for high and low temperature fuel cells.     

Method for Increasing the Humidity in Polymer Electrolyte Membrane Fuel Cell

The water content within the polymer electrolyte membrane is essential to have good proton conduction and high efficiency of a fuel cell system. In this paper a new technique to increase the fuel cell efficiency acting on the internal humidity will be presented. In order to understand the potentialities and the limitations of such technique, the method was studied in a theoretical approach and then applied on a proton exchange membrane fuel cell (1 kW PEMFC) that supplies the energy for the traction of a prototype vehicle, which took part in the last Shell Eco‐marathon competition. Finally has been verified that the membrane water content is related to the hydrogen consumption and for some applications (e.g., military single‐use equipment), the “filling” method could be advantageous over humidified system and non‐humidified systems. To ensure the proper success of the procedure it is also applied the differential method to fault detection.     

Analysis of the Ripple Current in a 5 kW Polymer Electrolyte Membrane Fuel Cell Stack

Polymer electrolyte fuel cell systems are increasingly being used in applications requiring an inverter to convert the direct current (DC) output of the stack to an alternating current (AC). These inverters, and other time‐varying inputs to the stack such as the anode feed pressure, cause deviations from the average stack current, or ripple currents, which are undesirable for reasons of performance and durability. A dynamic fuel cell model has been developed and validated against experimental data for a 5 kW fuel cell stack, examining in detail the ripple current behaviour. It was shown that the ripple currents exceed the 2% maximum recommended value, and may lead to long‐term degradation of the fuel cell stack.     

Membranbrennstoffzellen

With the development of polymer membranes suitable as proton‐conducting electrolytes, membrane fuel cells are now successfully applied in various areas. Depending on the application, the service life, the power density or other system aspects are optimized. Common to all applications is the requirement to reduce costs, which, however, plays a decisive role especially in passenger cars. The development of the membrane fuel cell has now reached a high technical level, but political flanking measures are still required to launch it on the market. This applies both to the hydrogen infrastructure for fuel cell vehicles and to the promotion of fuel cell‐based combined heat and power generation.     

Assessment of Fuel‐Cell‐Based Passenger Cars

Highly efficient energy conversion systems with fuel cells for vehicles, as well as for stationary and portable applications, are currently being discussed all over the world. Fuel cell technology is expected to help reduce primary energy demand and emissions of limited and climate‐relevant pollutants. The high flexibility of fuel cell systems with respect to energy carriers opens up possibilities of modifying the energy sector in the long term. Introducing new fuels based on low‐carbon, or in the long term carbon‐free, energy carriers can contribute to reducing greenhouse gas emissions as well as locally and regionally active atmospheric pollutants. The use of hydrogen as feed gas for fuel cells on the basis of it being a non‐fossil, renewable energy, leads to special benefits with respect to conserving resources and climate protection, but at present still represents a medium‐ to long‐term prospect. A major milestone on the road to market success for all energy conversion systems with fuel cells is the reduction of costs. The definition of the „appropriate” fuel represents a serious obstacle to the market introduction of fuel‐cell‐powered vehicles. Presenting data from a well‐to‐wheel analysis of various vehicle fuel systems at FZJ this article aims to discuss the potential benefits of future vehicle concepts with fuel cells in terms of primary energy use and greenhouse gas emissions. Results from a comparison of international studies on this subject will be used to identify relevant assumptions that lead to different answers in the evaluation process.     

Investigation of ethanol conversion for hydrogen fuel cells using computer simulations

Ethanol conversion to hydrogen has been investigated by a series of thermodynamic analyses and computer simulations within the context of a cost‐effective fuel processor/fuel cell system where heat exchange is of great importance. Two different methods, multi‐reaction equilibria and Gibbs free energy minimisation, are used for the thermodynamic analyses. The computer simulations consider the catalytic conversion of ethanol to hydrogen on a bimetallic Pt–Ni catalyst by indirect partial oxidation (IPOX) which consists of total oxidation (TOX), steam reforming (SR) and water–gas shift (WGS) reactions. The results indicate that there is an optimal water:fuel ratio for maximum hydrogen production at each operating condition for hydrogen yields calculated as a percentage of the theoretical value. Mass‐based hydrogen yields are also presented considering fuel economy especially for vehicular applications. Finally, the benefits of using a secondary WGS reactor and the comparison of the results of the two thermodynamic methods are highlighted. Copyright © 2005 Society of Chemical Industry     

Membrane Design for Direct Ethanol Fuel Cells: A Hybrid Proton‐Conducting Interpenetrating Polymer Network

A series of hybrid proton‐conducting membranes with an interpenetrating polymer network (IPN) structure was designed with the direct ethanol fuel cell (DEFC) application in mind. In these membranes, glutaraldehyde crosslinked poly(vinyl alcohol) (PVA) were interpenetrated with the copolymer of 2‐acrylamido‐2‐methyl‐propanesulphonic acid (AMPS) and 2‐hydroxyethyl methacrylate (HEMA) crosslinked by poly(ethylene glycol) dimethacrylate (PEGDMA). Silica from the in situ sol–gel hydrolysis of tetraethyl orthosilicate (TEOS) was uniformly dispersed in the polymer matrix. The membranes fabricated as such had ion exchange capacities of 0.84–1.43 meq g^–1 and proton conductivities of 0.02–0.11 S cm^–1. The membranes exhibited significantly lower fuel permeabilities than that of Nafion. In a manner totally unlike Nafion, fuel permeabilities were lower at higher fuel concentrations, and were lower in ethanol than methanol solutions. These behaviours are all relatable to the unique swelling characteristics of PVA (no swelling in ethanol, partial swelling in methanol and extensive swelling in water) and to the fuel blocking and swelling suppression properties of silica particles. The membranes are promising for DEFC applications since a high concentration of fuel may be used to reduce fuel crossover and to improve the anode kinetics for a resultant increase in both the energy and power densities of the fuel cell.     

AC‐Impedance Investigation of Different MEA Configurations for Passive‐Mode DMFC Mini‐Stack Applications

Membrane‐electrode assemblies (MEAs) characterised by different hydrophobic–hydrophilic properties were investigated in a passive Direct methanol fuel cell (DMFC) monopolar mini‐stack at room temperature. These properties were modulated by varying the amount of Nafion or replacing the ionomer in the catalytic layer with polytetrafluoroethylene (PTFE). Impedance spectroscopy provided valuable information with respect to the limiting processes occurring during fuel cell operation. Methanol crossover, especially in the presence of high methanol concentration, played a major role in determining the overall performance. The development of a methanol impermeable membrane appears crucial for increasing the performance of DMFC devices for portable applications.     

Fuel Cell Modeling Strategic Roadmap: A Systematic Approach

Polymer electrolyte fuel cells (PEFCs) are promising electrochemical devices for the direct conversion of chemical energy of a fuel into useful electrical work with vast applications in automotive, stationary, and autonomous power. It is widely recognized that progress in PEFC technology is a multi‐disciplinary challenge and hinges on Research and Development (R&D) breakthroughs in design, fabrication, and implementation of innovative materials, processes, and system optimization. Fuel cell modeling, in particular, has been the subject of intense research in the past two decades, as it is of great importance to design and process optimizations. Building upon the insights obtained in a European Collaborative Research Program, we present an analysis of fuel cell modeling R&D roadmap by focusing on technical and market attributes and the inter‐relations therein. The roadmap is driven by three distinct outcomes – alpha, beta and commercial versions, reflecting the maturity of the multi‐scale software. All roadmap entries are organized in layers, namely Market and Business; Services; Products; High Level Targets; Technology; Science; and Enablers and Resources. This study contributes to a much needed foundation for further planning of potential R&D and demonstration projects of fuel cells for automotive and other emerging sectors.     

Surface Fluorination of Poly(fluorenyl ether ketone) Ionomers as Proton Exchange Membranes for Fuel Cell Application

A series of sulphonated poly(fluorenyl ether ketone) ionomers were successfully fluorinated by the means of direct surface fluorination. Polymer ionomer samples in two different states (membrane and powder) were treated with F₂ gas which is diluted in N₂ in a special reactor. X‐ray photoelectron spectroscopy (XPS) was used to examine the F/C ratios of the fluorinated materials. The results revealed that the fluorination only occurred on the membrane surface and the fluorination degree increased with increasing F₂ concentration in N₂. The membrane subjected to fluorination shows an obviously enhanced oxidative stability. The endurance in a Fenton's reagent of FSPFEK‐P‐28 is longer than 180 min which is two times longer than that of un‐fluorinated SPFEK. The PEM properties and single fuel cell performances were investigated by comparison of un‐ and fluorinated polymer ionomers. The fluorinated membranes demonstrated an enhanced hydrophobic surface property, increased proton conductivities and better single fuel cell performances. Surface fluorination provides a convenient and useful approach to prepare highly proton conductive membrane with long life‐time PEM fuel cell applications.     

Advances in Mixed‐Reactant Fuel Cells

The mixed‐reactant fuel cell (MRFC) is a new concept, in which a mixture of aqueous fuel and gaseous oxygen (or air) flows directly through a porous anode‐electrolyte‐cathode structure or through a strip‐cell with an anode‐electrolyte‐cathode configuration. These structures can be single cells or parallel stacks of cells and may be in a planar, tubular or any other geometry. Selectivity in the electrocatalysts for MRFCs is mandatory to minimize mixed‐potential at the electrodes, which otherwise would reduce the available cell voltage and compromise the fuel efficiency. MRFC offers a cost effective solution in fuel cell design, since there is no need for gas‐tight structure within the stack and, as a consequence, considerable reduction in sealing, manifolding and reactants delivery structure is possible. In recent years, significant advances have been made in MRFCs, using methanol as a fuel. This paper reviews the status of mixed reactant fuel cells and reports some recent experimental data for methanol fuel cell systems.     

Vibration Modeling of PEM Fuel Cell for Prediction of Cell Number Effects by Experimental Data

One of the most important challenges in increasing the performance, reliability and lifetime of fuel cells is the mechanical load effects that occur on real applications. Therefore, the vibration model of fuel cell that predicts the behavior of various fuel cell layouts is very useful. The fuel cell is made up of different adjacent layers that may have semi opposite mechanical properties. This special structure leads to occurrence of non‐linear behavior of fuel cell under dynamic mechanical vibrations and so, a black box method is selected for modeling of its vibration behavior. In this study, the mechanical load experiments in various shape and axes were applied on five layouts of proposed fuel cell and the vibration of its body measure by some accelerometers. The NNARXM neural network is created and trained with the experimental data of three layouts of the fuel cell. Then, the prediction error of this neural network, validated with the two other experimental data of fuel cell layouts, by correlation coefficients and histogram of prediction errors. Neural network validation shows the well prediction of both untrained layout and suitable estimation for any desired layout.     

Modelling Approach for Planar Self‐Breathing PEMFC and Comparison with Experimental Results

This paper presents a model‐based analysis of a proton exchange membrane fuel cell (PEMFC) with a planar design as the power supply for portable applications. The cell is operated with hydrogen and consists of an open cathode side allowing for passive, self‐breathing, operation. This planar fuel cell is fabricated using printed circuit board (PCB) technology. Long‐term stability of this type of fuel cell has been demonstrated. A stationary, two‐dimensional, isothermal, mathematical model of the planar fuel cell is developed. Fickian diffusion of the gaseous components (O₂, H₂, H₂O) in the gas diffusion layers and the catalyst layers is accounted for. The transport of water is considered in the gaseous phase only. The electrochemical reactions are described by the Tafel equation. The potential and current balance equations are solved separately for protons and electrons. The resulting system of partial differential equations is solved by a finite element method using FEMLAB (COMSOL Inc.) software. Three different cathode opening ratios are realized and the corresponding polarization curves are measured. The measurements are compared to numerical simulation results. The model reproduces the shape of the measured polarization curves and comparable limiting current density values, due to mass transport limitation, are obtained. The simulated distribution of gaseous water shows that an increase of the water concentration under the rib occurs. It is concluded that liquid water may condense under the rib leading to a reduction of the open pore space accessible for gas transport. Thus, a broad rib not only hinders the oxygen supply itself, but may also cause additional mass transport problems due to the condensation of water.     

An investigation of fuel composition and flow‐rate effects in a H2S fuelled sofc: Experiments and thermodynamic analysis

Hydrogen sulphide (H₂S)‐fuelled solid oxide fuel cells (SOFCs) can potentially generate useful electrical energy while disposing of H₂S, a toxic by‐product of the fossil fuel industry, on site. Experimental results from H₂S fuelled SOFCs exhibit characteristics, for example, an unusual dependence of cell performance on fuel composition and flow‐rate, which are poorly explained in the literature. In this work we: (a) present results for experiments where the composition and flow‐rates were varied for both the fuel and oxidant streams to analyse their effect on fuel cell performance, and (b) develop and use a thermodynamic analysis to help understand these experimental results. Through this work, we shed further light on two basic questions unanswered so far, (1) Why does the flow‐rate of the fuel affect the open circuit potential of the fuel cell? (2) Which of the chemical species present in the fuel is oxidised on the anode? Our experiments and analysis suggest that H₂S, and not H₂ produced from H₂S dissociation, is preferentially electro‐oxidised on the anode in our experiments. © 2011 Canadian Society for Chemical Engineering     

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.     

A Dynamic Simulation Tool for the Battery‐Hybrid Hydrogen Fuel Cell Vehicle

This paper describes a dynamic fuel cell vehicle simulation tool for the battery‐hybrid direct‐hydrogen fuel cell vehicle. The emphasis is on simulation of the hybridized hydrogen fuel cell system within an existing fuel cell vehicle simulation tool. The discussion is focused on the simulation of the sub‐systems that are unique to the hybridized direct‐hydrogen vehicle, and builds on a previous paper that described a simulation tool for the load‐following direct‐hydrogen vehicle. The configuration of the general fuel cell vehicle simulation tool has been previously presented in detail, and is only briefly reviewed in the introduction to this paper. Strictly speaking, the results provided in this paper only serve as an example that is valid for the specific fuel cell vehicle design configuration analyzed. Different design choices may lead to different results, depending strongly on the parameters used and choices taken during the detailed design process required for this highly non‐linear and n‐dimensional system. The primary purpose of this paper is not to provide a dynamic simulation tool that is the “final word” for the “optimal” hybrid fuel cell vehicle design. The primary purpose is to provide an explanation of a simulation method for analyzing the energetic aspects of a hybrid fuel cell vehicle.     

Development of a Micro Temperature Sensor and 3D Temperature Analysis for a Proton Exchange Membrane Fuel Cell

This study examines the development of micro in situ sensors and analyzed the through‐plane temperature of a fuel cell. Temperature sensing inside a fuel cell is important in fuel cell diagnosis and analysis. Temperature sensors must be adequately small, so that fuel cell performance is maintained and the temperature anywhere inside the cell can be flexibly measured. In this study, a temperature sensor based on a micro‐electromechanical system (MEMS) is designed and fabricated to achieve these objectives. The micro temperature sensor was installed inside a cell to measure through‐plane temperature. The current and voltage of the fuel cell with the micro temperature sensor were measured and compared with those of a fuel cell without the sensor to analyze the effect of the sensor on fuel cell performance. The developed temperature sensor is of resistance temperature detector (RTD) type, with a flexible substrate of polyimide, high sensitivity, and easy installation characteristics. After calibration of the sensors, three sensors were inserted into the cell to measure the through‐plane temperature, and the polarization curve of the cell with and without the micro sensor was compared. Finally, a 3D computational fluid dynamics (CFD) model of a fuel cell was developed and analyzed by comparison of the measured temperature results to determine the accuracy of the model.     

Current Status of and Recent Developments in the Direct Methanol Fuel Cell

The direct methanol fuel cell (DMFC) has been discussed recently as an interesting option for a fuel‐cell‐based mobile power supply system in the power range from a few watts to several hundred kilowatts. In contrast to the favoured hydrogen‐fed fuel cell systems (e.g. the polymer electrolyte membrane fuel cell, PEMFC), the DMFC has some significant advantages. It uses a fuel which is, compared to hydrogen, easy to handle and to distribute. It also comprises a fairly simple system design compared to systems utilising liquid fuels (like methanol) to produce hydrogen from them by steam reforming or partial oxidation to finally feed a standard PEMFC. Nevertheless, many severe problems still exist for the DMFC, hindering its competitiveness as an option to hydrogen‐fed fuel cells. This work reviews the major research activities concerned with the DMFC by highlighting the problems (slow kinetics of the anodic methanol oxidation, methanol permeation through the membrane, carbon dioxide evolution at the anode) and their possible solutions. Special attention is devoted to the steady state and dynamic simulation of these fuel cell systems.