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Download – Literature |
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Dear Fuel Cell Industry Participant,
As an added service to the fuel cell industry, FuelCon offers this database of informative publications and reports related to fuel cell testing and diagnostics. This is being made available to encourage dialogue, ideas, and flow of information within the fuel cell community with the ultimate goal of accelerating product development and commercialization. If you have publications that you wish to share with the fuel cell community, please send an email to: publication@fuelcon.com and we will include it within this database.
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Title |
AC Impedance Diagnosis on a 500W PEM Fuel cell Stack |
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Authors |
Yuana, Suna, Blancoa, Wanga, Zhanga, Wilkinsona
Institute for Fuel Cell Innovation, National Research Council Canada
(05/2005, Lit0209, 1 Page, 190 kb) |
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| Abstract |
| AC Impedance or Electrochemical Impedance Spectroscopy (EIS) has been demonstrated to be a useful and powerful technique to analyze the origin of the performance losses in a fuel cell. Although many approaches have been used with EIS, most studies on the PEM fuel cell have focused on single cells. Only limited EIS work has been done on fuel cell stacks, especially on stacks with practical active areas. The main purpose of this study is to present diagnostic information from AC impedance measurements on a 500W PEM fuel cell stack on a Evaluator test station from FuelCon with respect to the effects of temperature, flow rate and humidity. |
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Title |
THE TECHNIQUE OF THE DIFFERENTIAL IMPEDANCE ANALYSIS Part I: BASICS OF THE IMPEDANCE SPECTROSCOPY |
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Authors |
Vladikova
Institute of Electrochemistry and Energy Systems– Bulgarian Academy of Sciences
(09/2004, Lit0210, 28 Pages, 869 kb) |
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| Abstract |
| This review paper gives basic knowledge about the Electrochemical Impedance Spectroscopy (EIS). The main working hypotheses for its correct performance are discussed. A detailed presentation of the structural modelling is made. A brief introduction of the basic elements and electrochemical models is done. The different steps of the impedance data analysis: data pre-processing, parametric identification and selection of the best model are all described in more details. |
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Title |
TrueData-EIS - Impedance spectrum analyzer |
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Authors |
FuelCon
(03/2005, Lit0211, 10 Pages, 2.1 Mb) |
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| Abstract |
| The TrueData-EIS is a device for measuring the impedance of MEA´s, single fuel cells and stacks. Using the single sine technique the TrueData-EIS provides precise measurement of the real and the imaginary part of impedance and the magnitude and phase angle of the test item compared with the current interrupt method. Its fully digital design assures high accuracy measurement and easy integration into automated test systems. The graphical user interface allows rapid navigation through its logical menu system.The TrueDate-EIS provides impedance data for a range of frequencies and currents that are of greatest interest to the fuel cell research community. |
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Title |
Protocol on Fuel Cell Component Testing (USFCC 04-003) |
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Authors |
US Fuel Cell Council
(11/2004, Lit0070, 22 Pages, 304 kb) |
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Abstract |
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USFCC and the fuel cell industry are very
interested in the potential effects of impurities in hydrogen on the
performance of fuel cells. USFCC has generated a series of documents
to support the effort on investigating these impurities. The intent
of these documents is to give guidance to the investigators so that
test data that is collected will be sufficient to generate numeric
models to predict the performance of a cell with time. The purpose
of this document is to supply guidance to the fuel cell industry on
the testing of fuel impurities on Proton Exchange Membrane (PEM) electrodes.
This guidance is in the form of a primer for generating test plans.
This primer addresses the types of testing and the sequence of testing
required by the industry to generate the test data necessary for determining
the effects of an impurity on the performance of a fuel cell. |
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Title |
Influence of the Membrane Ion Exchange Capacity on the Catalyst Layer of Proton Exchange Membrane Fuel Cell |
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Authors |
Navessin
University of London
(10/2004, Lit0081, 176 Pages, 1.8 Mb) |
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| Abstract |
| This work investigates the effect of ion exchange capacity (IEC) of polymer electrolyte membranes (PEM) on the PEM fuel cell cathode catalyst layer. Oxygen electrochemistry, mass transport properties, water absorption behavior, and proton conductivity were studied in relation to the IEC. Electrochemical characterization including cyclic voltammetry, electrochemical impedance spectroscopy and linear sweep voltammetry were employed. The agglomerate model for cathodes was adapted and used to extract mass transport parameters from experimental results. Prior to investigation in fuel cell system, studies were performed in a half-fuel cell, which simplified complicating parameters associated with fuel cell operation. It was found, that membranes with higher IEC resulted in a higher active surface area of electrode. In contrast, they exhibit lower oxygen reduction performance. The membrane´s IEC regulates the extent of flooding of the cathode, which in turn affects its electrochemical characteristics. The investigation under operating fuel cell conditions revealed an increase in fuel cell performance with increasing IEC. This is explained by the interplay of electroosmotic flux and hydraulic counterflux in the membrane which affects water management in the membrane electrode assembly (MEA). The influence was most significant in the cathode catalyst layer, where it affects mass transport and electrochemical characteristics. It was found that the higher IEC facilitated better water management in MEAs. Comparing results obtained with half-fuel cell and fuel cell systems revealed insights into the state of hydration and effective use of Pt in the catalyst layer. The two types of measurements provide a convenient approach to study the interplay of different mechanism of water flux in the membran. These will be discussed in this work. |
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Title |
Investigations of Proton Conducting Polymers and Gas Diffusion Electrodes in the Polymer Electrolyte Fuel Cell |
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Authors |
Gode
KTH, Chemical Engineering and Technology
(07/2004, Lit0078, 68 Pages, 1.4 Mb) |
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| Abstract |
| The primary purpose of the thesis was to develop experimental techniques and to use them to characterize proton conducting polymers and membranes for PEFC applications electrochemically at, or close to, fuel cell operating conditions. The work presented ranges from polymer synthesis to electrochemical characterization of the MEA performance. The use of a sulfonated dendritic polymer as the acidic component in proton conducting membranes was demonstrated. In order to study gas permeability a new in-situ method based on cylindrical microelectrodes was developed. An advantage of this method is that the measurements can be carried out at close to real fuel cell operating conditions, at elevated temperature and a wide range of relative humidities. The durability testing of membranes for use in a polymer electrolyte fuel cell (PEFC) has been studied in situ by a combination of galvanostatic steady-state and electrochemical impedance measurements (EIS). Long-term experiments have been compared to fast ex situ testing in 3 % H2O2 solution. For the direct assessment of membrane degradation, micro-Raman spectroscopy and determination of ion exchange capacity (IEC) have been used. The influence of ionomer content on the structure and electrochemical characteristics of Nafion-based PEFC cathodes was also demonstrated. The electrodes were thoroughly investigated using various materials and electrochemical characterisation techniques. Electrodes having medium Nafion contents (35<x<45 wt %) showed the best performance. The mass-transport limitation was essentially due to O2 diffusion in the agglomerates. Furthermore, models for the membrane coupled with kinetics for the hydrogen electrode, including water concentration dependence, were developed. The models were experimentally validated using a new reference electrode approach. The membrane, as well as the hydrogen anode and cathode characteristics, were studied experimentally using steady-state measurements, current interrupt and EIS. Data obtained with the experiments were in good agreement with the modelled results. |
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Title |
Experimental Validation of a PEM Fuel Cell Model by Current Distribution Data |
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Authors |
Ju, Wang
Pennsylvania State University (ECEC)
(06/2004, Lit0130, 7 Pages, 833 kb) |
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| Abstract |
| A three-dimensional, electrochemical-transport coupled model is applied to a 50 cm² proton exchange membrane (PEM) fuel cell and validated against the current distribution data experimentally measured earlier. A parallel computational methodology is employed to substantially reduce the computational time and make large-scale calculations involving millions of grid points possible. Simulation results are analyzed and validated against the available experimental data of current distribution under fully humidified conditions for two cathode stoichiometry ratios. The comparisons of simulations and experiments point out a lack of agreement in the current distribution, although the average polarization curves are matched nearly perfectly. The numerical simulations correctly capture the comma-shaped local polarization curves observed in the current distribution experiments.. |
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Title |
Effect of cathode structure on planar free-breathing PEMFC |
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Authors |
Hottinen, Himanen, Lund
Laboratory of Advanced Energy Systems, Helsinki University of Technology
(06/2004, Lit0085, 6 Pages, 227 kb) |
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| Abstract |
| The effect of cathode structure on the performance of planar free-breathing fuel cell is studied. Three different types of gas diffusion backings and current collector plates on the cathode were used. The gas diffusion backings used were thick carbon sheet, titanium sinter, and carbon paper. Difference between current collector plates was the size of the openings between current collecting ribs. Results showed that with thicker gas diffusion backings the structure of the current collector had only some effect on the cell performance but with thin carbon paper the effect was significant. Very high power densities for free-breathing fuel cell were achieved with thin gas diffusion backing with the record of approximately 360mW/cm². However, the cell was also vulnerable for flooding as there was liquid water observed on the cathode surface. Despite the liquid water saturation it seems that this kind of cell design may be suitable especially for portable applications. |
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Title |
Model and Evaluation of a Tubular Solid Oxide Fuel Cell |
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Authors |
Springman
(04/2004, Lit0134, 24 Pages, 584 kb) |
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| Abstract |
| A model of a tubular solid oxide fuel cell is developed and used to evaluate performance criteria given three variables of interest, (1) Fuel Cell Temperature, (2) Fuel Flow rate, and (3) Load Voltage. The model considers the enthalpy, entropy, and exergy of the inflowing and out flowing streams. Hydrogen with a small fraction of water vapor is taken as the fuel stream, while air is taken to compose the reactant stream. However, for the later only the bulk gases of nitrogen and oxygen are considered. Temperature dependence of the reaction rate and conductivities are also accounted for. Focus is given to the second law efficiency and exergy generation due to both the thermal dissipation and mixing of the exiting streams with the ambient. The maximum efficiency for the analyzed configuration and geometry is close to 35% for normal operating conditions when only the power obtained across the load voltage is considered. Fuel utilization, voltage efficiency and exergy generation are also evaluated in detail for the three scenarios. |
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Title |
AC IMPEDANCE INVESTIGATION OF FLOODING IN MICRO FLOW CHANNELS FOR FUEL CELLS |
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Authors |
Cha, O Hayre, Prinz
Stanford University
(01/2004, Lit0124, 5 Pages, 434 kb) |
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| Abstract |
| This paper presents a study on the transport phenomena related to gas flow through fuel cell micro-channels, specifically the impact of dimensional scale on the order of 100 microns and below. The use of structural photopolymer (SU-8) enabled the direct fabrication of functional fuel cell micro-channels. Previous experimental observation has revealed that if flow channels are too small, they may reduce the performance of fuel due to flooding. For further investigation, AC Impedance technique has been employed to measure the mass transfer resistance. The result confirmed that in smaller channels, mass transportation resistance increases due to the flooding. |
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Title |
Effect of Relative Humidity on Catalytic Activity of Oxygen Reduction in Proton Exchange Mebrane Fuel Cells |
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Authors |
Song, Kunz, Fenton
University of Connecticut
(01/2004, Lit0012, 1 Pages, 95 kb) |
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| Abstract |
| In addition to an explanation of the functionality and the construction of PEMFCs, this article gives information about the influence of the reactant relative humidity (RH) on the performance of the fuel cell. In this regard, AC impedance spectra and polarization curves were measured at four different temperatures each with six variations of the RH factor. The result of this experimental examination is, that during the range of 20-50% of humidity the overpotential decreases significantly with increase in relative humidity. Higher than 50%, the change with relative humidity is very little. The corresponding AC impedance results also demonstrate the same tendency. Furthermore, this article shows connections between the RH factor and the activity of the protons, and the amount of the hydroxide ions. |
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Title |
Ion exchange resin/polystyrene sulfonate composite membranes for PEM fuel cells |
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Authors |
Chena, Krishnana, Srinivasana, Benzigerb, Bocarslya
Department of Chemistry, Princeton University
(01/2004, Lit0101, 7 Pages, 330 kb) |
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| Abstract |
| A new composite proton exchange membrane was made by casting a polystyrene sulfonate (PSS) solution with suspended micron sized particles of a crosslinked PSS ion exchange resin. The chemical compatibility of the resin and the PSS allow stable composites with up to 50 wt.% resin. The resin/PSS composite membranes have greater ion exchange capacity than PSS membranes, but the ion conductivity is similar to that of PSS. Swelling of the composite membranes as a function of water uptake is lower than that of PSS. The composite membranes are mechanically more robust and display greater chemical stability in a fuel cell than the PSS membranes. The polarization curves show long-term degradation of the membranes; the cell potential decreased by 60% in 55 h for a PSS membrane, and in 340 h for a composite membrane. The reduced rate of degradation of the composite membranes suggests that with further refinement they may have potential as an inexpensive alternative for PEM fuel cells. |
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Title |
Fuels Paradise? How can Chemistry find a way out of the energy crisis? |
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Authors |
Quadt
University of Bath
(01/2004, Lit0115, 19 Pages, 282 kb) |
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| Abstract |
| The title of this literature research project is a challenging one: How can chemistry find a way out of the energy crisis? That an energy crisis is at hand is a commonly accepted fact, also that the burning of fossil fuels is very inefficient and creates heavy pollution. In this paper it is shown, that chemistry (in combination with physics, engineering etc.) offers some means to get out of the energy crisis, namely the technology. What is also needed is political and social acceptance and the backing and understanding that it must put an end to the reliance on fossil fuels. What will the future look like then? There are many paths to get there but most people share the opinion, that we are going towards a hydrogen future. Fuel cells are going to be the major energy sources in the upcoming decades and centuries. The most pressing question is however, how the hydrogen is going to be supplied, i.e. what the infrastructure is going to look like. This will be outlined in chapter 6, hydrogen can be produced from many different sources and it looks like using fossil fuels for hydrogen production would be the easiest option, as it can use the existing infrastructure. This refers to the cover picture of this paper: renewable sources of energy (solar, hydro, biomass, geothermal) can be used to produce hydrogen, effectively leaving us with one of the cleanest energy systems imaginable. The most optimistic thinkers outline a future with decentralized power systems. An electric grid would not be necessary anymore (at least not in the current size), reducing losses from resistance and prohibiting power outages. In this paper the general working principle of Fuel cells in Chapter 1; briefly discuss the physics behind Fuel Cells in Chapter 2; introduce different FCs in Chapter 3; and have a look at the latest research on fuel cell catalysts in Chapter 4. Finally, this paper comments on Safety in Chapter 5 and finishs with Chapter 6 on Hydrogen Production and Storage. |
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Title |
Advanced MEA technology for Hydrogen and Reformate PEMFC Application |
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Authors |
Koehler
Umicore
(11/2003, Lit0046, 23 Pages, 2.2 Mb) |
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Abstract |
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In this presentation, the basic technical
necessities for MEAs will be described custom-designed. Moreover, the
development of the electrodes as well as the used catalysts of the
cathode (hydrogen system) and of the anode (reformate system), and
possible solutions to improve the MEA subcomponents with the main focus
on the performance and the life time of the MEA are discussed. In addition
to this, different illustration facilities are investigated concerning
their advantages and disadvantages. To give examples, the tafel plot
technique is used for the development of the cathode catalyst, the
EIS is used for the development of the electrodes as well as for the
design of the equivalent schematics, and the polarization measurements
on the anode is used to observe degradation effects. As exerimental
examples, the life time and performance will be characterized. |
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Title |
The Air/Platinum/Nafion Tripl-Phase Boundary: Characteristics, Scaling and Implications for Fuel Cells |
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Authors |
O`Hayre, Prinz
Stanford university
(11/2003, Lit0049, 7 Pages, 1.4 Mb) |
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Abstract |
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This contribution examines the heterogeneous
kinetics of the oxygen reduction reaction (ORR) at the Pt/Nafion/air
triple-phase boundary (TPB). This system is of particular interest
for low-temperature polymer electrolyte membrane fuel cell applications.
A focused ion beam system is used to prototype geometrically simple
platinum microstructures directly on Nafion electrolyte membranes.
By varying the size and shape of the platinum structures, the role
and properties of the TPB are elucidated. Currentvoltage and electrochemical
impedance spectroscopy measurements reveal that the ORR kinetics scale
with TPB length. A faradaic resistance per unit TPB length of 6*10^9
Ohm µm is extracted under short-circuit conditions at room temperature.
Although this value is determined from microscopic measurements of
geometrically simple platinum structures, it is successfully applied
to predict the bulk performance of large-area sputtered platinum catalyst
fuel cells. |
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Title |
Standardlösungen für die Brennstoffzellenprüfung |
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Authors |
Mathias Bode
FuelCon
(10/2003, Lit0139, 2 Pages, 0.9 kb) |
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| Abstract |
| The present article describes the state-of-the-art in the field of test technology for fuel cells. Following the description in headwords of the components of a fuel cell test rig, the generell structure of a fuel cell test system is drafted. Furthermore, the safty requirements are specified, that means the arrangements which have to be taken to obviate the incidence of explosion capable atmospheres. Also it is shown which labeling at the test rigs it has to be attend to, in this regard. Then the article discusses the several types of test rigs such as the MEA, stack and the system as well as the component test rigs in regard to the qualification and their applications. Finally, this paper gives an outlook of the direction of the further development and the enhancement of those test rigs. |
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Title |
Development and characterization of a silicon-based micro direct methanol fuel cell |
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Authors |
Lua, Wang, Yen , Zhang
Pennsylvania State University, Electrochemical Engine Center (ECEC)
(09/2003, Lit0129, 8 Pages, 325 kb) |
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| Abstract |
| A silicon-based micro direct methanol fuel cell (µDMFC) for portable applications has been developed and its electrochemical characterization carried out in this study. Anode and cathode flowfields with channel and rib width of 750µm and channel depth of 400µm were fabricated on Si wafers using the microelectromechanical system (MEMS) technology. A membrane-electrode assembly (MEA) was specially fabricated to mitigate methanol crossover. This MEA features a modified anode backing structure in which a compact microporous layer is added to create an additional barrier to methanol transport thereby reducing the rate of methanol crossing over the polymer membrane. Extensive cell polarization testing demonstrated a maximum power density of 50 mW/cm² using 2M methanol feed at 60 °C. When the cell was operated at room temperature, the maximum power density was shown to be about 16 mW/cm² with both 2 and 4M methanol feed. It was further found that the present µDMFC still produced reasonable performance under 8M methanol solution at room temperature. |
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Title |
Ultra-Thin Composite membrane-electrode Assembly for High-Temperature Proton Exchange Membrane Fuel cells |
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Authors |
Yuh, Kopp, Patel
Fuel Cell Energy Inc
(08/2003, Lit0044, 4 Pages, 214 kb) |
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Abstract |
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The objectives of this article are the
presentation, as well as the solution of the technical problems with
regard to the development of a ultra thin composite for a MEA of a
high temperature PEMFC, such as the purity of the hydrogen, the carbon
monoxide cleaning, and the thermical as well as the water management.
Thereby, the membrane should be durable and long-living, and must be
able to endure a operating temperature in the range of 100-140 °C.
In addition to this, it should have a very small membrane resistance,
and hence a very high ionic conductivity with negligible conductivity
of electrons. Furthermore, a high mechanical
capacity is aimed. |
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Title |
EXPERIMENTAL DIAGNOSTICS OF PEM FUEL CELLS |
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Authors |
Mughal
University of Waterloo
(07/2003, Lit0080, 64 Pages, 778 kb) |
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| Abstract |
| The introduction of this presentation gives the basic knowledge concerning to a PEMFC, their components, as well as their functions. Also, the consequences of the operation conditions on the performance of the cell are explained. In addition to this, this presentation gives an extensive literature review with a description of the content of several of these citations in headwords. Following this, the experimental equipments given here are discussed in regard to the selection of the parameters, specifications of the test cell, and the test apparatus. Furthermore, the most important measuring techniques for the characterization of the fuel cells are explained, the ideal management of the cell in regard to the influence of the humidification as well as the water transport in a fuel cell are elucidated. Also, it is described how the parameters have to be varied to achieve ether the drying or the flooding of the cell. To that effect, it is illustrated what the selection of a high as well as a low temperature, pressure, and stoichiometric ratio causes to the performance of the fuel cell and the finding of the best parameters for the pressure, temperature, and the relative humitidy of the anode and cathode is shown. Moreover, the presentation shows an example of an automatical test station as well as various examples of program flow sequences in script language for the accomplishment of a full automatic measurement, and discusses the experimental results concerning to the ohmic polarization and the limitation effects on the reactants regarding miscellaneous curves, which were taken by variegating the parameters discussed before. In addition to this, a detailed modelling of an electrical equivalent circuit of a fuel cell is given. Finally, the results which were simulated with that circuit are compared to those which were measured. |
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Title |
ENHANCEMENT OF CARBON MONOXIDE TOLERANCE IN PROTON EXCHANGE MEMBRANE FUEL CELLS |
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Authors |
Escribano, Fourneron
CEA-Grenoble
(06/2003, Lit0122, 3 Pages, 292 kb) |
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| Abstract |
| One of the drawbacks to the development of Proton Exchange Membrane Fuel Cells (PEMFCs) using reformed fuels is the presence of carbon monoxide (CO) in the reformate which drastically decreases the performance by poisoning the anodic catalyst. The enhancement of CO tolerance should help to simplify hydrogen processing and therefore to reduce the cost of fuel cell systems. That is why this article deals with the CO poisoning of anodes in proton exchange membrane fuel cells. Experiments have been carried out to observe the influence of the anodic catalyst composition and of the operating temperature. Furthermore, this article gives a description of the used cell and its components respectively as well as the materials used for the experimental accomplishment. In this writting the study of the voltage drop caused by CO poisoning on the polarization curve as well as the voltage stability after few hours of poisoning and recovery of the performances when feeding the anode with pure hydrogen is shown. After that, the results obtained are then discussed in detail. The conclusions on one hand are that it has been shown that in particular conditions (80°C, high pressure) CO tolerance can be enhanced by adding a small amount of Mo to PtRu. On the other hand, enhancement of the CO tolerance can easily be performed with a standard catalyst like PtRu only by increasing the temperature above 120°C. However at low pressure, this implies to find solutions for the electrolyte and the humidification. As a conclusion, it should be possible with an optimized tri-metallic catalyst to reach a high CO tolerance even in usual operating conditions (Tcell; 100°C and low pressure). |
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Title |
Investigation on Storage Technologies for Intermittent Renewable Energies: Evaluation and recommended R&D strategy |
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Authors |
Boulanger, Perrin
CEA-GENEC
(06/2003, Lit0117, 45 Pages, 2.1 Mb) |
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| Abstract |
| In the storage of electricity via hydrogen, one crucial element is the fuel cell since it may be the element with the lowest maturity. For this reason, in the first paragraph, the fuel cell technology is described precisely. Then the application of the fuel cell as a part in a storage system for renewable energy is described. In first line the fuel cell must be fed with a fuel that, in the case of a storage system based on renewable energy, is hydrogen. Hydrogen can be produced by different methods that are described. Secondly, independently on the method by which it is produced, hydrogen must be stored before it will be used in the fuel cell. Therefore the different technologies for hydrogen storage are reviewed. This report is meant at centralising information about renewable energy storage by means of electrolysis, hydrogen storage and fuel cell utilisation and does not pretend to be exhaustive. |
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Title |
Three-dimensional computational analysis of transport phenomena in a PEM fuel cell, a parametric study |
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Authors |
Berning, Djilali
Institute for Integrated Energy Systems, University of Victoria
(06/2003, Lit0111, 13 Pages, 811 kb) |
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| Abstract |
| This paper presents the results of a parametric study conducted with a previously described three-dimensional, non-isothermal model of a polymer electrolyte membrane (PEM) fuel cell. The effect of various operational parameters such as the temperature and pressure on the fuel cell performance was investigated in detail. It was found that in order to obtain physically realistic results experimental measurements of various modelling parameters were needed. The results show good qualitative agreement with experimental results published in the literature. In addition, geometrical and material parameters such as the gas diffusion electrode (GDE) thickness and porosity as well as the ratio between the channel width and the land area were investigated. The contact resistance inside the cell was found to play an important role for the evaluation of the impact of such parameters on the fuel cell performance. The results demonstrate the usefulness of this computational model as a design and optimization tool. |
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Title |
Development of novel self-humidifying composite membranes for fuel cells |
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Authors |
Liu, Yi, Xing, Yu, Hou, Fu
Fuel Cell RD Center, Dalian Institute of Chemical Physics
(05/2003, Lit0131, 9 Pages, 362 kb) |
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| Abstract |
| A novel preparation method for self-humidifying membranes of proton exchange membrane fuel cells (PEMFCs) was developed. Using solution-cast method, PTFE porous substrates in these composite membranes can increase their strength and distribute self-humidifying layers adjacent to the anode side. Compared with the cells fabricated with ordinary membranes, the performance of the cells with these self-humidifying proton exchange membranes (PEMs) are dramatically improved in both cell voltage and the current density under dry conditions, and the cell using the Pt/C-PEM shows the best and most stable performance. EIS technique revealed that these self-humidifying composite membranes could minimize membrane conductivity loss under dry conditions. |
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Title |
Introduction to Fuel Cell Technology |
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Authors |
Rayment, Sherwin
Department of Aerospace and Mechanical Engineering, University of Notre Dame
(05/2003, Lit0079, 156 Pages, 2.1 Mb) |
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| Abstract |
| This work is divided into three parts. Prefacing, a facile description of the fuel cell basics is given, which is recessed in one of the sections below. Moreover, the introduction contains the historical fuel cell technology background and finally, the question why fuel cells are the items of research at all, will be resolved. The second part of this work discusses the basics of fuel cell more detailed. In this regard, problems like the maximum obtainable voltage of the open circuit, and the efficiency of a fuel cell, as well as the reasons for the loss of voltage are addressed. Furthermore, all conventional fuel cell types are explained very detailed concerning to their performance, configuration, and their parameters of operation. The secluding part of this work illustrates the actual and future applications and objects of research of the fuel cells. Among that, explainations concerning to fuel cell components, the production processes of the hydrogen out of natural gas, coal gas, and biological fuel, as well as the simulation and control of a PEMFC, and the costs analysis amongst others the possibilities of cost reducing are given. |
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Title |
Applications to SOFC |
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Authors |
Tuller, Hertz, Lappalainen
Massachusetts Institute of Technology
(05/2003, Lit0050, 28 Pages, 1.9 Mb) |
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Abstract |
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The main objective of this presentation
is to answer the question how to create a mechanically stable and pinhole
free thin electrolyte. The discussion about this question leads to
a technique, which is called the grain boundary engineering. According
to this, the presentation shows the challenges and opportunities. Furthermore,
this work discusses different deposition methods to produce those thin
electrolyte films. After that, the characterization of the microstructures
of these deposited films is accomplished, mainly with techniques like
AFM (atomic force microscopy) and XRD (x-ray diffraction). In addition
to this, the CV-measurements and the impedance spectroscopy are explained
on a MOS-capacitor considering as example. Finally, the approach of
the micro fuel cell performance is illustrated. |
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Title |
In-line Regelung der Methanolkonzentration in einem Brennstoffzellen Teststand |
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Authors |
Köllmann
PSI Paul Scherrer Institut
(03/2003, Lit0067, 79 Pages, 1.3 Mb) |
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| Abstract |
| At the beginning, this diploma thesis elucidates the thermodynamical and electrochemical basics of a DMFC such as the construction, the functional principle, as well as the open circuit operation, and the operation performance. Furthermore, the physical basics of the analytical concentration measurements i.e. the density measuring technique, the spectrospic methods, and concentration measuring with ultrasonic waves are described. Thereby, the evaluation of these different concentration measurement methods mainly takes place in regard to the sensitivity, the costs, and the aim. Concerning to this, constructive and experimental problems are discussed. Among these things there are to mention the environment of test stands, its modification, dimensioning, and calibration. Moreover, the experimental part of this work deals with the characterization of fuel cells with the help of measured current-voltage curves. |
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Title |
NEW POLYMER ELECTROLYTE MEMBRANES FOR FUEL CELLS OPERATING ABOVE 100;C- APPROACHES AND RECENT PROGRESS |
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Authors |
Li, Jensen, He, Bjerrum
Department of Chemistry, Technical University of Denmark
(03/2003, Lit0116, 15 Pages, 379 kb) |
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| Abstract |
| The state-of-the-art of PEMFC technology is based on perfluorosulfonic acid (PFSA) polymer membranes operating at a typical temperature of 80°C. The newest development in the field is alternative polymer electrolytes for operation above 100°C. This paper is devoted to a review on the development, which is classified into three groups: modified PFSA membranes, alternative sulfonated polymer and their inorganic composite membranes and acid-base complex membranes. High temperature PEMFC has been demonstrated with advanced features such as fast electrode kinetics, high CO tolerance, simple thermal and water management and possible integration with the fuel processing unit. |
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Title |
SIMULATION STUDY OF A PEM FUEL CELL SYSTEM FED BY HYDROGEN PRODUCED BY PARTIAL OXIDATION |
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Authors |
Ozdogan, Ersoz, Olgun
Marmara University
(01/2003, Lit0120, 13 Pages, 231 kb) |
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| Abstract |
| Within the frame of sustainable development, efficient and clean, if possible zero emission energy production technologies are of utmost importance in various sectors such as utilities, industry, households and transportation. Low-temperature fuel cell systems are suitable for powering transportation systems such as automobiles and trucks in an efficient and low-emitting manner. Proton exchange membrane (PEM) fuel cell systems constitute the most promising lowtemperature fuel cell option being developed globally. PEM fuel cells generate electric power from air and hydrogen or from a hydrogen rich gas via electrochemical reactions. Water and waste heat are the only by-products of PEM fuel cells. There is great interest in converting current hydrocarbon based common transportation fuels such as gasoline and diesel into hydrogen rich gases acceptable by PEM fuel cells. Hydrogen rich gases can be produced from conventional transportation fuels via various reforming technologies. Steam reforming, partial oxidation and autothermal reforming are the three major reforming technologies. In this paper, the results of a simulation study for a PEM fuel cell with partial oxidation are discussed. Two liquid hydrocarbon fuels have been selected to investigate the effect of average molecular weights of hydrocarbons, on the fuel processing efficiency. The overall system efficiency depends on the fuel preparation and fuel cell efficiencies as well as on the heat integration within the system. It is desired to investigate the overall system efficiencies for net electrical power production at100 kW considering bigger scale transport applications. Results indicate that fuel properties, fuel preparation system operating parameters and PEM fuel cell polarization curve characteristics all affect the overall system efficiency. |
|
| |
Title |
Hardware Development For Impedance Spectroscopy on A 4-Cell PEMFC Stack Under Load |
| |
Authors |
Merida, Harrington, McLean, Djilali
University of Victoria
(01/2003, Lit0011, 9 Pages, 491 kb) |
| |
| Abstract |
| This article gives a functional description concerning to the so called EIS (Electrochemical Impedance Spectroscopy). It shows the objective of this measuring method which is the developement of an equivalent electrical model for the system under investigation. The reader gets useful informations about the hardware required to measure the impedance as a function of frequency directly. In addition to this, he learns which information he can extract out of these measured spectra. But the quantitative analysis of these spectra is not part of this article. It only refers to further reading. Also, this work addresses two failure modes that are particular to PEMFC stacks under real operating conditions. Referring to this, it describes an experimental examination on a stack which consists of 4 small cells connected in series, and separated by water-heated compartments. This design makes it possible to control the delivery and conditioning of reactants to each individual cell. Result of this analysis is that the difference in potential between normal and flooded cells can be significant even at moderate current densities, which is particularly significant for high currents. To illustrate this potential difference, the measured polarization curves of the individual cells are shown in contrast. |
|
| |
Title |
Interpretation of Impedance Spectra with State-Space Modelling |
| |
Authors |
Prestat, Gaukler
ETH Zürich
(01/2003, Lit0020, 1 Pages, 100 kb) |
| |
| Abstract |
| This citation is a scientific poster which gives a concise description according to the development of fuel cell impedance models. The objective of this writing is the presentation of the numerical simulation of the electrochemical impedances with the help of a meaningful and efficient attempt, the so called state-space modelling. This modelling is the evidence of the interpretation of the measured impedance spectra. Furthermore, the results of the simulations accomplished are compared to the experimental impedance data. The models established, are then assessed to their quality. This poster also includes illustrations according to the oxygen reduction mechanisms an the kinetic at the SOFC cathodes. |
|
| |
Title |
Modelling Impedance Diagrams of Fuel Cell |
| |
Authors |
Bulte, Le Gorrec, Diard, Walkievicz
Laboratoire d'Electrochimie et de Physico-Chimie des Matériaux et Interfaces
(01/2003, Lit0019, 1 Pages, 111 kb) |
| |
Abstract |
| |
The present article describes the alignment
of a dc and ac model of the fuel cell impedance. According to the dc
and ac current measurements, this model also includes the contributions
which can be allocate to the internal resistance, the kinetic of the
oxygen reduction, the hydration oxidation, and to the mass transport
the gas diffusion layer. Admittedly, in the approach of this model
the diffusion and the ohmic drop in the active layer were disregarded.
In particular, an equivalent electrical circuit for the PEMFC is developed
and on this basis, diagrams of the impedance are simulated. Furthermore,
this article explains the development of the semicircles in the nyquist
plot, allocates this semicircles to the physical phenomena as well
as the elements of the equivalent circuit. |
| |
|
| |
Title |
Chemical Modification of Fuel Cell Catalysts and Electrochemistry of Proton Exchange Membrane Fuel Cell Electrodes |
| |
Authors |
Easton
Department of Chemistry, Memorial University of Newfoundland
(01/2003, Lit0082, 220 Pages, 1.3 Mb) |
| |
| Abstract |
| One of the major goals of this research was to investigate ion transport within the catalyst layer of fuel cell electrodes and attempt to improve it. One method used to study ion transport within fuel cell electrodes was to incorporate electroactive metal complexes into the catalyst layer to act as a probe. It was found that a lower fraction of the complexes were electrochemically active in the cathode of an operating fuel cell, compared to similar electrodes in contact with an aqueous sulfuric acid solution. It is anticipated that in many cases, the method of electroactive probes will be more advantageous than (or complimentary to) standard methods. Electrochemical impedance spectroscopy was also used to study ion transport in fuel cell catalyst layers. It was found that limiting capacitance correlates with active area. Also, results indicate that the non-ideal impedance behavior of fuel cell electrodes is due to variation of their ionic conductivity with distance from the membrane. In order to increase proton conductivity in the catalyst layer, it was explored the attachment of a sulfonated silane directly to the catalyst surface. Another major goal of this work was to study the materials from which direct methanol fuel cells (DMFC) are constructed. Here the systematic optimization of all membrane-electrode assembly components is reported, using standard fuel cell materials. This has led to significant improvement in performance. |
|
| |
Title |
In Situ Current Distribution Measurements in Polymer Electrolyte Fuel Cells |
| |
Authors |
Mench, Wang, Ishikawab
Electrochemical Engine Center and Department of Mechanical and Nuclear Engineering (ECS)
(01/2003, Lit0084, 8 Pages, 1.1 Mb) |
| |
| Abstract |
| There has been much recent interest and development of methods to accurately measure the current distribution in an operating polymer electrolyte fuel cell (PEFC). This paper presents results from a novel technique that uses a segmented flow field with standard, nonaltered membrane electrode assemblies and gas diffusion layers. Multiple current measurements are taken simultaneously with a multichannel potentiostat, providing high-resolution temporal and spatial distribution data. Current distribution data are shown that display the distributed effects of cathode stoichiometry variation and transient flooding on local current density. It is shown that the time scale for liquid accumulation in gas diffusion layer pores is much greater than that of any electrochemical or gas-phase species transport process. In order to facilitate state-of-the-art PEFC model validation, an idealized single-pass serpentine flow field was used, and the exact geometry is presented. |
|
| |
Title |
Effect of ambient conditions on performance and current distribution of a polymer electrolyte membrane fuel cell |
| |
Authors |
Hottinen, Noponenen, Mennola, Himanen, Mikkola,
Lund
Helsinki University of Technology, Laboratory of Advanced Energy Systems
(01/2003, Lit0086, 7 Pages, 342 kb) |
| |
| Abstract |
| 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 effcient oxygen transport to the electrode. Furthermore, varying the air humidity resulted in major changes in the mass diffusion overpotential at higher temperatures. |
|
| |
Title |
Intermediate Temperature SOFC based on fully intergrated Plasma sprayed Componets |
| |
Authors |
Ma, Hui, Zhang, Dai, Roth, Xiao, Reisner
Inframat Corp, US Nanocorp
(01/2003, Lit0047, 6 Pages, 582 kb) |
| |
Abstract |
| |
This work addresses the fabrication of
membrane-type SOFCs, operating at an intermediate temperature using
all components fabricated by plasma spray technology, and to evaluate
the performance of the SOFC single unit at a temperature range of 500-800 °C.
Single cells composed of a LaSrMnO3 (“LSM”) cathode, LaSrGaMgO3
(“LSGM”) electrolyte and a Ni/YSZ anode, were fabricated
in successive atmospheric plasma spraying processes. Plasma spraying
processes have been optimized and tailored to each layer in order to
achieve a high porosity cathode or anode layer as well as a high density
electrolyte layer. Major effort has been devoted to the production
of the LSGM electrolyte film with high density and free-cracking. Electrochemical
impedance spectroscopy was used to investigate the conductivity of
the electrode layers and particularly the resistance of the electrolyte
layer. It was revealed that the heat treatment had a great influence
on the specific conductivity of the sprayed electrolyte layer, and
that the specific conductivity of the heattreated one was dramatically
increased to the same magnitude as that of a sintered LSGM pellet.
The experimental results have demonstrated that the plasma spray process
has great potential for the integrated fabrication of the medium temperature
SOFC units. |
| |
|
| |
Title |
Diffusion media materials and characterization |
| |
Authors |
Mathias, Roth, Fleming, Lehnert
General Motors, Adam Opel AG
(01/2003, Lit0098, 21 Pages, 1.4 Mb) |
| |
| Abstract |
| Incipiently, many specific functions of a gas diffusion media is declared in this report. Following this, it speculates about the future development of PEMFCs. Furthermore, this article describes a novel carbon-based diffusion media and compares it with conventional models. In addition to this, the fabrication process is explained step by step as well as the alternative methods for production of the carbon-fiber papers are shown and compared in regard to their efficiency. Also, the treatment of such diffusion media as well as the characterization methods used here like the electrical conductivity, mechanical characterization, investigation of the thickness, porosity, and the pore size distribution, fluid permeability, surface energy as well as the characterization of the fuel cells with current contribution as function of temperature and polarization curves. According to this, this report gives a detailed description of the function and the accomplishment of the particular characterization method as well as their mathmatical descriptions. |
|
| |
Title |
A fuel cell model for building cogeneration applications |
| |
Authors |
Ferguson, Ugursal
Canadian Residential Energy Enduse Data and Analysis Centre
(01/2003, Lit0073, 8 Pages, 844 kb) |
| |
Abstract |
| |
In this article, a quasi steady state model for cogeneration PEM fuel cell systems has been developed for use in integrated building simulation. The model can predict the fuel cell system fuel use, and heat and electricity production in response to building loads. The modelling, including theory, structure and validation is discussed, and preliminary results demonstrating the model’s use with a building simulation program are presented. Also, this article addresses economical reasons for the research on fuel cells. Following this, a comparison of the performance of both the thermal engine (Carnot cycle) and the fuel cell, concerning to the degree of efficiency, costs, and ecological damage is done in this work. Moreover, it gives a detailed description of the several subsystems of a fuel cell, i.e. the fuel cell stack, the fuel processor, and auxiliary systems. It discusses the three types of the polarization losses, gives the substantial electrochemical and thermodynamical knowledge to understand the following parametric modelling approach, and shows how the model architecture as well as the validation, and preliminary results are done and derivated, step by step. |
| |
|
| |
Title |
An In Situ Method for Determination of Current Distribution in PEM Fuel Cells Applied to a Direct Methanol Fuel Cell |
| |
Authors |
Mench, Wang
(11/2002, Lit0097, 7 Pages, 152 kb) |
| |
| Abstract |
| This paper describes and demonstrates a new method for determination of current density distribution in an operating polymer electrolyte membrane (PEM) fuel cell. The technique is a modification of the current mapping technique that relies on an array of shunt resistors embedded within a current collecting plate. Standard, nonaltered membrane electrode assemblies are utilized with gas diffusion layers in direct contact with an electrically segmented current collector/flow field. Multiple current measurements are taken simultaneously, allowing transient distribution detection with a multichannel potentiostat. Both steady state and transient data are presented for an operating liquid fed direct methanol fuel cell. Cathode flooding is predicted, and shown to occur at relatively high cathode flow rates. This technique can contribute to knowledge and understanding of key phenomena including water management and species distribution in PEM fuel cells. |
|
| |
Title |
Entwicklung von Kathodenstrukturen für die Hochtemperatur-Brennstoffzelle SOFC |
| |
Authors |
Weber
(07/2002, Lit0113, 179 Pages, 11.8 Mb) |
| |
|
| |
Title |
Transmission Line Modeling |
| |
Authors |
Chen, Waraksa, Cho, Mcdonald, Mallouk
(06/2002, Lit0014, 9 Pages, 628 kb) |
| |
Abstract |
| |
Porous electrodes provide high-surface-area
supports for the catalysts of many reactions, but the influences of
electrode preparation conditions on electrocatalysts are not always
well understood. Electrochemical impedance spectroscopy (EIS) can provide
extensive information about an electrode, but the models describing
the spectra are often too idealized to draw useful conclusions. This
article describes a new model based on an array of parallel, nonuniform
transmission lines for predicting the response of porous electrodes.
The model incorporates physically realistic elements, such as discrete
particles of variable size and adjustable multilayer stacking geometries.
Resistance parameters were derived from experimental data for Pt4Ru4Ir-coated
Ti0.9Nb0.1O2 and Ebonex electrodes prepared under varying degrees of
oxidative conditioning. The results, which indicate a high degree of
impedance at the support-solution interface and consequently, low catalyst
utilization, suggest several strategies for improved electrode design. |
| |
|
| |
Title |
Impedance of Oxide Catalyst Supports |
| |
Authors |
Chen, Waraksa, Cho, Mcdonald, Mallouk
(06/2002, Lit0013, 6 Pages, 542 kb) |
| |
| Abstract |
| In this paper two titanium oxide catalyst supports for the oxygen electrode of unitized regenerative fuel cells were compared by electrochemical impedance spectroscopy (EIS) techniques. One was a commercial Ebonex sample, which is a mixture of Ti4O7 and the other conductive Magneli phases, and the other was a niobium-doped rutile oxide, Ti0.9Nb0.1O2 . Both supports were loaded with a mixed Ir-Ru-Pt oxide catalyst and conditioned anodically. The impedance spectra shows a resistive component which can be assigned, using transmission line modeling of the catalyst/support/electrode structure, to the series resistance of the support particles. Although both supports increase in resistance with anodic conditioning, the increase is greater for Ebonex. This increase in support resistance is consistent with oxidation of TiIII to TiIV, which appears to be reversible in the case of the Nb-doped rutile material but irreversible with Ebonex.. |
|
| |
Title |
SOFCs for Direkt Oxidation of Hydrocarbon Fuels with Samaria-Doped Ceria Electrolyte |
| |
Authors |
Lu, Worell, Gorte, Vohs
(06/2002, Lit0015, 5 Pages, 249 kb) |
| |
Abstract |
| |
Samaria-doped ceria (SDC) electrolyte-supported
solid oxide fuel cells (SOFCs) with Cu-SDC and Cu-CeO2-SDC anode composites
were fabricated. Current-voltage and impedance-spectroscopy measurements
were used to characterize their performance at temperatures between
600 and 700°C. The cells demonstrated the ability to directly utilize
not only hydrogen (H2) but also dry butane (C4 H10) fuel. At 700°C,
the maximum power density of a cell with a Cu-CeO2-SDC anode composite
was 246 and 170 mW/cm2 for H2 and C4H10 fuels, respectively. Impedance
spectra suggested that for butane fuel, the anode resistance significantly
limits the overall cell performance. It was shown that the addition
of pure ceria to the anode significantly increased the catalytic activity
for oxidation reactions and decreased the anode resistances. |
| |
|
| |
Title |
HYDROGEMS; Hydrogen energy models |
| |
Authors |
Ulleberg, Glöckner
(06/2002, Lit0114, 12 Pages, 284 kb) |
| |
| Abstract |
A collection of hydrogen energy models (HYDROGEMS) for simulation of integrated renewable energy (RE) hydrogen (H2) systems has been developed at Institute for Energy Technology (IFE, Norway). The HYDROGEMS library includes component subroutines for photovoltaic (PV) arrays, wind energy conversion systems, diesel engine generator systems, advanced alkaline water electrolysis, high-pressure hydrogen gas storage, proton exchange membrane fuel cells (PEMFC), alkaline fuel cells (AFC), compressors, power conditioning equipment, and logical control functions. The models have been tested and
verified against various hydrogen energy demonstration plants around the world. HYDROGEMS is compatible with a transient system simulation program (TRNSYS) and an engineering equation solver (EES), which make the models particularly useful for system design and optimization of control strategies for integrated RE/H2-systems.
|
|
| |
Title |
A sharp peak in the performance of sputtered platinum fuel cells at ultra-low platinum loading |
| |
Authors |
O´Hayre, Lee, Cha, Prinz
(03/2002, Lit0038, 11 Pages, 441 kb) |
| |
Abstract |
| |
Proton exchange membrane fuel cells were
fabricates by direct sputter deposition of platinum of Nafion 117 membranes.
A sharp spike in the performance of these sputtered platinum fuel cells
was observed at ultra-low platinum thickness values of 5-10 nm. Within
this narrow thickness range, the power output capability of sputtered
platinum fuel cells is several orders of magnitude better than the
performance produced by thinner or thicker coatings. The spike in performance
is explained by rapid changes in the sputtered film microstructure
at the nanometer thickness level. When the membrane surface is deliberately
modified by abrasion prior to sputtering, this sharp peak is not seen.
Instead, a broad plateau is observed, where the performance is insensitive
to the amount of sputteres platinum. This behavior stems from how surface
roughening affects the sputtered catalyst layer continuity. The performance
of a sputter-deposited membrane with a platinum loading level of 0.04
mg/cm_ is compared to a commercial membran electrode assembly (MEA)
with a platinum loading of 0.4 mg/cm_. The maximum power output of
the sputtered cell is three-fifths that of the commercial MEA, but
uses one-tenth the platinum. |
| |
|
| |
Title |
Model of the Air System Transients in a Fuel Cell Vehicle |
| |
Authors |
Bird
(01/2002, Lit0128, 143 Pages, 3.8 Mb) |
| |
| Abstract |
| This thesis describes a procedure to measure the transient effects in a fuel cell air delivery system. These methods were applied to model the 20 kW automotive fuel cell system that was used in Animul H2, a fuel cell-battery hybrid sedan developed by a group of engineering students at Virginia Tech. The air delivery system included the air compressor, the drive motor for the compressor, the motor controller, and any plumbing between the fuel cell inlet and the compressor outlet. The procedure was to collect data from a series of tests of the air delivery system with no load (zero outlet pressure) and at several loads. The air compressor speed, outlet pressure, and motor controller current were measured in response to a variety of speed requests. This data was fit to transfer functions relating the compressor speed, outlet pressure, or motor controller current to the speed request. The fits were found using a least squares optimization technique. After the experimental model was developed, it was augmented with an analytical model of the rest of the fuel cell system. The mass flow of the air was determined from the air compressor speed and outlet pressure with the compressor map. The fuel cell current was found by assuming a constant stoichiometric ratio. The power out of the fuel cell was calculated from the fuel cell current and the pressure with the polarization curve. The model of the fuel cell system was implemented in Matlab/Simulink. Several open and closed loop simulations were run to test the functionality of the fuel cell system model. The gross and net powers of the fuel cell system were found as a function of the compressor operating speed. The time it took for the system to come up to power as a function of idle speed was also found. A PID controller was implemented to allow the system to track a reference power request. The key contributions of this work were to develop a method to test the air delivery system to determine the dynamics of the system, to develop a model based on these tests and some analytical knowledge of fuel cells, and to use the model to simulate the operation and control of a fuel cell system. |
|
| |
Title |
Praktikum Brennstoffzellen |
| |
Authors |
Stefener
(01/2002, Lit0108, 37 Pages, 622 kb) |
| |
| Abstract |
| The present guidance of a practical course provides general basics about the fuel cell technology. According to this, the alkaline, the PEM, the phosphoric acid, molten carbonate as well as the oxide ceramical fuel cell with regard to the historical background, applications, operation mode with the help of a layout and the possible problems during the application are discussed respectively. Following this, the functionality of fuel cells is particular elucidated for the PEMFC in detail. In this regard, the reason and the use of a gas diffusion layer as well as its funcionality and elucidations according to the advantages and disadvantages of the sandwich construction or the stack construction are discussed respectively. In addition to this, the thermodynamics of a fuel cell is explained with mathmatical derivation and physical description as well. Furthermore, after the explainations of knowledge about the kinetics and the thermodynamics, the lost mechanisms are discussed with a typical current-voltage-map. Also, the typical polarization curves of the several fuel cell kinds are shown in this guidance. Experimental, explainations about the connection of specific resistance to the water content, the distribution of the reversible cell voltage as a function of pressure and temperature as well as the transport activities in a membran are given in detail. Finally, useful advices about the accomplishment of those measurements and calculations of the desired data are shown respectively. |
|
| |
Title |
Experimental Studies on Polymer Electrolyte Membrane Fuel Cell Stacks |
| |
Authors |
Mikkola
(12/2001, Lit0089, 106 Pages, 1.4 Mb) |
| |
| Abstract |
| Fuel cells are electrochemical devices that convert chemical energy of the fuel into electricity at high efficiency without combustion. Fuel cells are viewed as viable power sources for many applications, including ground transport, distributed power generation and portable electronics. This thesis deals with experimental studies on Polymer Electrolyte Membrane Fuel Cell (PEMFC) stacks. PEMFC is a low temperature fuel cell, in which a proton conducting membrane is used as the electrolyte. The commercial breakthrough of fuel cells is hindered by the high price of fuel cell components. Lower prices will be achieved by developing new materials and improving performance. For the development of real-world applications, more information about the on long-term endurance of fuel cell and new diagnostic methods are required. This thesis addresses these questions with an experimental approach. The emphasis of this work is on the diagnostic methods, material choices, and long-term stability. Novel method to measure the resistance of a unit cell in a fuel cell stack was developed. Current interruption method was applied to a stack and voltage transients in unit cells were observed using a fast voltage sampling device. Cell resistance values were calculated from the transient data. The method was found to be practicable and to provide reasonably accurate results. The effect of gas diffusion backing materials on the performance of fuel cells was studied in a single cell. Large performance differences were observed at higher current densities. Performance dependence on the intrinsic material properties was studied by gas permeability measurements. No correlation between gas diffusion backing permeability and fuel cell performance was discovered. Thus the permeability of all five tested materials was deemed adequate for fuel cell use and the performance differences were concluded to derive from water management properties of the gas diffusion backings materials. Long-term stability of the PEMFC stack built in the Laboratory of Advanced Energy Systems was demonstrated by operating it continuously without any problems for over nine days. The average operating power was ca. 12 watts. |
|
| |
Title |
PEM Fuel Cell Design, Engineering, Modeling and Diagnostic Issues |
| |
Authors |
Barbir
(11/2001, Lit0068, 30 Pages, 2 Mb) |
| |
Abstract |
| |
This presentation explains the fuel cell
development process with the help of a program flow chart. Moreover,
it discusses the role of the modeling process and that of the diagnostic
within a fuel cell development process. In addition to this, it gives
a list of the main components of a fuel cell, a description of the
stack design, and discusses questions in regard to the development.
This work also investigates the influence of the PEM thickness on the
cell resistance and the performance. Furthermore, the differences between
single cells and stacks, a modeling example with the FEM technique,
and the description of possible diagnostic techniques (i.e. polarization
curve, current interrupt, and ac impedance measurement) are given. |
| |
|
| |
Title |
Relaxation impedance as a model for the deactivation mechanism of fuel cells |
| |
Authors |
Schiller, Richter, Gülzow, Wagner
(05/2001, Lit0027, 4 Pages, 155 kb) |
| |
Abstract |
| |
The influence of carbon monoxide poisoning
on the platinum anode in a polymer electrolyte fuel cell was investigated
using electrochemical impedance spectroscopy (EIS). Impedance measurements
of the cell under constant load were performed at periodic time intervals.
Due to the poisoning effect of the carbon monoxide, the system changes
its state during the experiment. The reconstruction of quasi-causal
spectra was made possible using enhanced numerical procedures, especially
the time course interpolation and the Z-HIT refinement. The reconstructed
impedance spectra show a strong time dependence and exhibit pseudo-inductive
contributions at the low frequency part of the spectra which increase
during the experiment. Analysis of the spectra suggests that the
pseudo-inductive behaviour can be attributed to a surface relaxation
process of the anode. Furthermore, the influence of carbon monoxide
on the electrochemical behaviour of the contaminated fuel cell may
be interpreted by means of a Faraday impedance in addition to potential-dependent
hindrance of the charge transfer.
|
| |
|
| |
Title |
Die autokatalytische H2O2-Reduktion an Ag-Elektroden |
| |
Authors |
Eickes
(05/2001, Lit0058, 141 Pages, 1.9 Mb) |
| |
Abstract |
| |
This dissertation gives detailed basics
about investigation methods such as the cyclical voltametry, galvanostatic
measurements, and the EIS. The latter is explained more precisely.
In addition to the basics, the kinetic analysis of the faradayic impedance
for three independent variables are explained. Moreover, this work
discusses the electochemical measuring setup, and the used chemicals.
An additonal measuring method explained in this work, is the XPS technique
(X ray photoelectron spectroscopy). In the practical part of this dissertation,
EIS investigations on Ag electrodes as well as the kinetic analysis
of the electrode impedance of the system Ag/H2O2/HClO4 are done. In
this connection, the experimental measuring datas obtained and the
results of the simulation are compared with each other. |
| |
|
| |
Title |
Algorithm Development for Electrochemical Impedance Spectroscopy Diagnostics in PEM Fuel Cells |
| |
Authors |
Latham
(01/2001, Lit0018, 178 Pages, 2.3 Mb) |
| |
Abstract |
| |
In the beginning of this work, there is
shown an introduction of the different types of fuel cells, diagnostic
techniques, and backgrounds of the perturbations of fuel cells such
as perturbations of the watermanagement (flooding, drying) and catalyst
poisoning. Following this, this work is occupied with the electrochemical
impedance spectrosopy (EIS). It gives a detailed functional description
of the EIS, specifies the required devices for this measurement technique,
describes the execution of those measurements, and discusses the derivation
as well as the fitting of the equivalent electrical circuits to the
measured data. Furthermore, this publication gives a revealing exposition
regarding to the interpretation of the taken impedance spectra. According
to this, the measurement of the impedance can identify pertubations
and faults which not only appear in a drop of the cell voltage. In
addition to this, the developed models will be taken some statistical
tests (i.e. Chi-squared and F-test) to evaluate their deviations and
the validity respectively. For deviations that are not negligible,
factors for correction are calculated. The general ambition of this
work is the development of algorithms to identify pertubations of fuel
cells with the help of electrochemical impedance spectroscopy (EIS).
The reason for this intention is to set on the design and development
of diagnostic hardware and test stations for fuel cells respectively.
Referring to this, it is also given a detailed description of the experiments
accomplished, and the results obtained. |
| |
|
| |
Title |
Modelling of Thermodynamic Fuel Cell Systems |
| |
Authors |
Nielsen, Bang, Bach
(01/2001, Lit0105, 18 Pages, 242 kb) |
| |
| Abstract |
| Fuel cell research has, so far, primarily focussed on the fuel cell stack itself, while research regarding modelling and optimization of the entire system is still in its infancy. This work focuses on developing a model of a PEM fuel cell stack and to integrate it with the external system needed for supplying the right conditions for a PEMFC. The sensitivity of the different stack-parameters has been investigated using the model. A thermodynamic model of such a system has been developed using the thermodynamic simulation tool EES (Engineering Equation Solver). Using a system model, parameters for optimum performance have been investigated - in particular the effect of pressurization. |
|
| |
Title |
Validation and evaluation of electrochemical impedance spectra of systems |
| |
Authors |
Schiller, Richter, Gülzow, Wagner
(09/2000, Lit0031, 5 Pages, 215 kb) |
| |
Abstract |
| |
The influence of hindered water removal
from a polymer electrolyte fuel cell under constant load was investigated
using electrochemical impedance spectroscopy. The cathodic gas outlet
of the cell was closed and impedance measurements were performed
at periodic time intervals. Under the experimental conditions, the
investigated system is far from steady-state conditions. It is shown
that enhanced mathematical techniques are required for evaluation
of the impedance data obtained. These techniques, the time course
interpolation as well as the Z-HIT refinement, lead to quasi-causal
spectra which are well interpreted by means of the porous electrode
model.
|
| |
|
| |
Title |
The Electrochemistry of Solid Oxide Fuel Cell Anodes |
| |
Authors |
Bieberle, Anja
(06/2000, Lit0064, 232 Pages, 1.3 Mb) |
| |
Abstract |
| |
This dissertation yields a very precise
overview abut the EIS method as well as their characteristical parameters.
Particularly concerning to the SOFC, this work gives wide informations
about the used materials, the microstructur of the oxide, as well as
the kinetic of the reaction occured.Especially for the realization
of the modeling, the state-space approach is axplained, and a comparison
of the experimental results with the simulated ones is done. Furthermore,
experimental studies about different material systems are shown in
this work. |
| |
|
| |
Title |
Development and Evaluation of a Test Apparatus for Fuel |
| |
Authors |
Davis
(05/2000, Lit0126, 98 Pages, 602 kb) |
| |
| Abstract |
| The development of a test apparatus for proton exchange membrane fuel cells is presented. The design of the prototype device is provided in detail along with a description of the apparatus. The evaluation of the functionality and effectiveness of the device included measurement | | |
