bluuebunny/crossref_metadata_2025_split huggingface dataset:
Highly durablePFSAmembranes
Authors: Endoh E. 
Published: December 2010

AbstractPerfluorosulfonic acid (PFSA) polymers are extensively applied for preparing the membrane of proton exchange membrane fuel cells (PEMFCs) because of their considerably higher chemical stability over hydrocarbon‐based polymers. However, even PFSA polymers suffer from decomposition caused by the hydroxyl radicals under low humidity conditions. Additionally, a critical breakdown of the membranes occurs at high temperatures when using conventional PFSA polymers, which have glass transition temperatures of around 80 °C. Therefore, operational conditions of PEMFCs are limited to low temperatures (below 80 °C) and high humidity conditions (ca 100% RH (relative humidity)).Highly durable PFSA membranes have been developed, which can operate for more than 6000 h at 120 °C and 50% RH. This achievement has opened up a new era of operating PEM fuel cells in the temperature range of near freezing to 120 °C under low and high humidity conditions for an extended period of time. In this article, a unique philosophy is presented along with guiding principles for developing highly durable PFSA membranes and their performances.
Factors influencing ionomer degradation
Authors: Inaba M. , Yamada H. 
Published: December 2010

Abstract
Chemical degradation of perfluorinated sulfonic acid (PFSA) membranes during operation is a serious problem to be overcome before commercialization of electric vehicles and stationary cogeneration systems based on polymer electrolyte fuel cells (PEFCs). In this article, the mechanism for peroxide/radical formation, which works as an active species for membrane degradation, in the cell is reviewed comprehensively. Accelerating factors, such as low humidification and open‐circuit conditions, and the effect of air bleeding are also discussed. Finally, the chemistry of PFSA membrane degradation is outlined, together with recent improvements in the durability of PFSA membranes.
Mechanical stability
Authors: Atkinson A. , Marquis A. J. 
Published: December 2010

AbstractThis article summarizes the approach to assessing the mechanical stability of solid oxide fuel cell (SOFC) ceramic materials and cell structures. The sources of stress are reviewed and their potential relaxation by creep is discussed together with the approach that is taken to calculate the complex stress distributions that arise in a working SOFCs. The alternative approaches to failure of brittle ceramics based on critical stress (strength) and fracture mechanics are described and illustrated using examples of stability of thin layers and probability of delayed fracture of an electrolyte. The critical stress approach is then illustrated in a more complicated example of a repeat‐unit channel in an anode‐supported SOFCs. The methodology illustrates how the cumulative probability of failure of the unit can be estimated as it passes through manufacture, initial commissioning, and representative duty cycles.
New oxide cathodes and anodes
Authors: Kilner J. A. , Irvine J. T. S. 
Published: December 2010

Abstract
Many of the key issues facing solid‐oxide fuel cell (SOFC) technology development may be addressed by finding improved electrode materials. These include lower temperature of operation, fuel flexibility, and sulfur and chromium tolerance. Here we review recent advances in anode and cathode materials design, focusing particularly on perovskite materials and their ordered structures, including intergrowths. Materials discovery, synthesis, fabrication, and evaluation are discussed. Particular emphasis is given to design of multifunctional composites at the nano‐ and microscales.
Factors limiting the low temperature operation of
SOFCs
Authors: Carter J. David , Cruse T. A. , Ingram B. J. , Krumpelt M. 
Published: December 2010

Abstract

Over the history of solid oxide fuel cell (SOFC) development, many investigators have sought to reduce the operating temperature. In this article, we present and discuss factors that lead to a lower limit on the effective operating temperature of these fuel cells. Among these factors, the cathode polarization resistance and fuel oxidation on the anode show the greatest effects on limiting low‐temperature operation. The strontium‐doped lanthanum manganite cathode is limited to ≥800 °C for 0.6 W cm
−2
at 0.85 V. Mixed‐ionic and electronic conducting materials are more active and can operate at ∼750 °C, but they are more prone to interact with the yttria‐stabilized zirconia (YSZ) electrolyte. Modified Ni‐based/YSZ anodes operating on carbonaceous fuels have a thermodynamic temperature limit of 500 °C because of carbon formation in the absence of steam, but also need to have their power densities improved to operate below 650 °C. The electrolyte resistance is not a significant factor for 8 mol% YSZ being able to operate as low as 530 °C, and for other electrolytes at even lower temperatures. Also, the electrical resistance of the interconnect, including that of the protective scale on metallic interconnects, becomes significant at temperatures below 600 °C. Cell geometry is another factor that limits low‐temperature operation, favoring planar over other stack designs.
Heat and water transport models for polymer electrolyte fuel cells
Authors: Pasaogullari U. 
Published: December 2010

Abstract
Owing to conflicting requirements of membrane hydration and avoiding flooding by liquid water, water management is very critical for polymer electrolyte fuel cells (PEFC). Water saturation pressure is strongly dependent on temperature around the PEFC operating temperatures. Therefore water transport and water management are strongly dependent on temperature distribution and thermal transport within the fuel cell. In this article, heat and water management in PEFCs is explored with a focus on modeling of the coupled heat and water transport. Effect of membrane hydration on fuel cell operation and performance is investigated in detail. Heat generation in PEFCs is described and breakdown of heat sources is given, and models describing the thermal transport and temperature distribution are reviewed. Coupled two‐phase heat and mass transport is elucidated along with the results from the computational models describing the phenomena.
Proton exchange membrane fuel cell (PEMFC) down‐the‐channel performance model
Authors: Gu W. , Baker D. R. , Liu Y. , Gasteiger H. A. 
Published: December 2010

AbstractThis article presents a down‐the‐channel model for proton exchange membrane fuel cell (PEMFC) performance prediction needed in system modeling and in fuel cell component selection for automotive application. With focus on the quantification of voltage loss terms, we have reviewed the required input physical‐chemical parameters for the model and the methods to obtain those kinetic and transport parameter values. Constructed based on multiple one‐dimensional cell models coupled with down‐the‐channel gas flow, the model is formulated to meet the high computational efficiency required by the system modeling aiming at improving fuel cell performance without incurring significant cost increase. With no free fitting parameters, the model is validated with reasonably good agreement against the experimental data, including cell performance, current distribution, and water balance, obtained from the short stacks with large active area and straight‐channel flow fields under subsaturated operating conditions desired for automotive application. Therefore, while further fundamental understanding and improvement of measurement techniques to obtain fundamental materials properties are needed, the down‐the‐channel model that quantifies the various voltage loss terms is a valuable tool for predicting stack performance with new materials under various new sets of operating conditions.
Performance during start‐up of proton exchange membrane (PEM) fuel cells at subfreezing conditions
Authors: Thompson E. L. , Gu W. , Gasteiger H. A. 
Published: December 2010

AbstractThis article discusses recent performance studies of PEM (proton exchange membrane) fuel cells operating at subfreezing temperatures. The major sources of voltage loss (kinetic, ohmic, and transport) are experimentally isolated to quantify their contribution to the total voltage loss. Thus, the oxygen reduction reaction (ORR) kinetics and membrane proton conduction resistances are quantified at subfreezing temperatures. To provide a mechanistic explanation for the observed temperature and water‐content dependency of proton conductivity, phase transitions and state of absorbed water in Nafion®was measured using differential scanning calorimetry.While it is reasonably well known that a successful PEM fuel cell cold start strongly depends upon the effective use of membrane and electrode to store product water (ice) until the cell temperature reaches 0 °C, the exact water (or charge) storage capacity of the membrane and the cathode electrode as well as the estimated water partitioning into these two locations as a function of operating conditions has not been discussed in detail and is presented here. In addition, cryo‐SEM is used to examine ice formation in the electrode and confirm the above estimates. The electron proton conduction resistance was used to predict the ORR current distribution within the cathode electrode, which provides insight into how ice filling proceeds in the electrode, and is supported by cryo‐SEM findings. Finally, the measured and estimated voltage losses are summarized to highlight the contribution of the various voltage loss terms on the overall initial voltage loss during operation at −20 °C, for a wide range of membrane water contents and current densities.
Use of neutron imaging for proton exchange membrane fuel cell (PEMFC) performance analysis and design
Authors: Trabold T. A. , Owejan J. P. , Gagliardo J. J. , Jacobson D. L. , Hussey D. S. , Arif M. 
Published: December 2010

AbstractEfficient water management is one of the key design objectives for proton exchange membrane fuel cells (PEMFCs) due to the influence of water on material selection, bipolar plate design, and operating conditions. Neutron imaging has proven to be one of the most important diagnostic methods available for PEMFC research, as the technique affords the ability to observe,in situ, water transport and accumulation phenomena. In this article, we provide an overview of the neutron imaging method, in terms of both the imaging technique itself, as well as special considerations for fuel cell test article design. Descriptions of specific applications areas are provided, including water gradients normal to the membrane‐electrode assembly, diffusion media and flow field channel water management, multicell and transient phenomena, and low temperature and freeze performance. Finally, we offer perspectives on future developments in the application of neutron imaging to fuel cells.
Modeling the impact of cation contamination in a polymer electrolyte membrane fuel cell
Authors: Greszler T. A. , Moylan T. E. , Gasteiger H. A. 
Published: December 2010

Abstract

Starting from fundamental principles, we have developed an isothermal, one‐dimensional model for cation contamination of a proton exchange membrane (PEM) fuel cell. When current is drawn, the foreign cations migrate toward the cathode under the influence of the potential gradient while diffusion acts to balance this migration. The model provides the electrolyte potential along with the concentration of water, cation, and proton across the membrane electrode assembly (MEA) at steady‐state condition. The voltage loss associated with cation contamination is largely thermodynamic in nature owing to the proton concentration (pH) difference that develops between the anode and cathode. This potential loss is proportional to current density and inversely proportional to water content. If the cation fraction in the cathode approaches unity, the cell current becomes limited because of proton starvation. The model is validated with experimental hydrogen pump performance data using lithium‐doped MEAs. Hydrogen/oxygen operation is presented experimentally and discussed, but not explicitly modeled because of the added complications introduced by the sluggish oxygen reduction reaction kinetics. Experimental data for cobalt‐doped MEAs, which can react in the cathode when the local pH increases above five, is presented and explained with the aid of cobalt's Pourbaix diagram. Finally, the effect of cobalt ion contamination (e.g., from PtCo cathode catalysts degradation) on H
2
/air PEMFC performance under automotive conditions is shown.
Electrochemical impedance spectroscopy as diagnostic tool
Authors: Jensen S. H. , Hjelm J. , Hagen A. , Mogensen M. 
Published: December 2010

Abstract
The aim of electrochemical impedance spectroscopy (EIS) is to gain knowledge about those processes that contribute to the impedance of an electrochemical system such as a fuel cell or just a single electrode. Usually several processes contribute, and they typically overlap in impedance spectra. This sets a limit to the amount of knowledge that can be derived about the individual processes. First, a brief review of the literature is given. Next, a method to separate individual contributions by systematic variation of operating parameters is described. Only processes depending on the variation contribute to the difference in the impedance. This makes it easier to analyze the difference than the impedance itself. The derivative with respect to ln(frequency) of the real part of the difference of the impedance spectra is easy to obtain and provides a good resolution of the contributions.
Electron microscopy to study membrane electrode assembly (
MEA
) materials and structure degradation
Authors: Chatenet M. , Guetaz L. , Maillard F. 
Published: December 2010

Abstract

The mass production of proton exchange membrane fuel cell (PEMFC) for stationary or mobile applications requires long‐term durability and minimization of the voltage loss observed upon operation. The extent of PEMFC performance degradation depends on the type of materials composing the membrane electrode assembly (MEA), their manufacturing technique, their structure, and the operating conditions of the cell. Recently, electron microscopy (EM) has become a technique of choice to achieve a better understanding of the physical/chemical origin of the MEA degradation as a function of operation time. Unlike most other physical, chemical, and electrochemical
in situ
or
ex situ
techniques (global techniques), EM enables the identification of local changes to the various components of the MEA. For example, defect formation at the micrometer scale in the proton exchange membrane (PEM) and the active layer (observed by scanning electron microscopy), change of porosity and redistribution of the electrocatalyst at the nanometer scale (observed by field‐emission gun scanning electron microscopy (FEG‐SEM) and transmission electron microscopy (TEM)), or structure/composition degradation of electrocatalyst nanoparticles at the atomic scale (observed by high‐resolution transmission electron microscopy (HRTEM)) can be derived from EM. A combination of the conclusions derived from local EM observations with those derived from other global characterization techniques yields the determination of MEA degradation mechanisms and provides some important routes to improve the PEM fuel cell performance and durability.
Proton exchange membrane fuel cell degradation: mechanisms and recent progress
Authors: Madden T. , Perry M. , Protsailo L. , Gummalla M. , Burlatsky S. , Cipollini N. , Motupally S. , Jarvi T. 
Published: December 2010

AbstractWe report a selective review of the literature on proton exchange membrane (PEM) fuel cell degradation. The review begins with an overview of the essential driving forces that influence degradation rates. Thereafter, we summarize key mechanisms of and progress toward mitigating carbon corrosion, platinum dissolution, and membrane degradation. Finally, we summarize useful research directions, and also identify those that deserve less attention.
Cold‐start durability of membrane‐electrode assemblies
Authors: Wang C. Y. , Yang X. G. , Tabuchi Y. , Kagami F. 
Published: December 2010

Abstract

Durability of membrane‐electrode assemblies (MEAs) cycled under cold‐start conditions is reviewed. It is shown that MEAs cycled under 100 mA cm
−2
from −30 °C show no degradation after 100 cycles, but exhibit mild degradation after 150 cycles under 300 mA cm
−2
from −30 °C, and furthermore suffer severe degradation after 110 cycles under 500 mA cm
−2
from −20 °C. Transmission electron microscopy (TEM) and X‐ray diffraction using cross‐sectional samples of the aged MEAs further revealed three primary degradation mechanisms: (i) interfacial delamination between the cathode catalyst layer (CL) and membrane, (ii) cathode CL pore collapse and densification upon melting of a fully ice‐filled CL, and (iii) Pt particle coarsening and Pt dissolution in the perfluorosulfonic acid (PFSA) ionomer. The interfacial delamination and CL densification appear to be closely related to each other, and the key parameter to affect both is the ice volume fraction in the cathode CL after each cold‐start step. Eliminating or minimizing these two degradation processes could improve the MEA cold‐start durability by 280%. Mitigation strategies include improved gas purge prior to cold start, good MEA design, small start‐up current density, and low cell thermal mass.
Membranes and catalyst performance targets for automotive fuel cells
Authors: Iiyama A. , Shinohara K. , Iguchi S. , Daimaru A. 
Published: December 2010

AbstractMembrane and catalyst performance targets for automotive fuel cells are presented. The Fuel Cell Commercialization Conference of Japan (FCCJ) has worked with three automobile manufacturers in Japan to define the target performance, durability, and cost of fuel cells for transportation application, and in January 2007 produced a booklet describing them. This article provides an overview of these target values and highlights the durability parameters specifically required in the automotive application in relation to the current knowledge of degradation mechanisms of fuel cells. On the basis of this information, FCCJ has proposed a methodology for testing membrane‐electrode assemblies (MEAs) as an approach to the evaluation of materials for the two most important components: electrolyte membranes and electrode catalysts. This is intended to assist the development of materials that achieve the target durability, which is described below.
Field experience with portable
DMFC
products
Authors: Müller J. 
Published: December 2010

Abstract
Direct methanol fuel cell (DMFC) systems and their user acceptance have a critical pioneering role in the developing fuel cell markets. This article focuses on commercial aspects of early markets for DMFC products, selection criteria why these markets were chosen, and customer benefits. Then, the process of matching customer requirements with technical capabilities of state‐of‐the‐art DMFC systems is described. The frequently discussed technical challenges of DMFC technology (e.g., methanol crossover) are reviewed and discussed in light of real‐world experience on thousands of DMFC systems globally. An important result is that the focus of many scientific research projects is quite different from realties in the marketplace. It is concluded that better alignment of academic research with industrial needs is required in order to advance fuel cell technology further. Next, degradation mechanisms in real‐world applications are reviewed and compared with known degradation mechanisms under laboratory conditions. Again, significant discrepancies occur, which must be addressed by any company attempting to sell fuel cell systems commercially.
Design concepts and durability challenges for mini fuel cells
Authors: Gottesfeld S. 
Published: December 2010

Abstract

Recent developments in direct methanol fuel cell (DMFC) technology are described. Starting in 2006, early commercialization of DMFC power sources of 20–100 W for recreational vehicles and boats and, most recently, 1 kW level DMFC systems for forklift power source applications has taken place. This development clearly suggests a significant degree of maturity of mainstream DMFC technology. Further, very recent technology advancements have opened the door to DMFC power sources of high system simplicity, which is of special significance to micro‐fuel cell applications. They include a DMFC platform with direct supply of 100% methanol into the DMFC anode, based on spontaneous supply of water from the cathode to the anode within the cell, thereby eliminating any need for water pumping around the cell. Fuel utilization of the order of 90% is achievable even with methanol‐leaky poly(perfluorosulfonic acid) (poly(PFSA)) membranes under such direct supply of 100% methanol to the DMFC anode, by adjusting the feed of neat methanol to a stoichiometric flow rate near 1.1. Quantitative analysis is provided for the requirements to embed a DMFC power system into small spaces defined by sizes of consumer electronics devices. The results show that, while implementation of DMFC power sources for hand‐held or laptop power applications is feasible with present technology through the use of external chargers, embedding such power units inside hand‐held devices is awaiting increase of the DMFC power density achievable under the operation conditions relevant for hand‐held applications, from the present level of 50–100 to over 300 mW cm
−3
.
Overview of solid oxide fuel cell degradation
Authors: Yokokawa H. 
Published: December 2010

AbstractThis article summarizes the general features of the degradation behavior of those solid oxide fuel cells stacks/systems that have to meet the requirements for chemical as well as mechanical compatibilities in addition to normal requirements concerning respective cell components. Sealless tubular stacks developed for large stationary applications and exhibiting excellent durability are first analyzed (0.3%/1000 h for more than 70 000 h as cells and 0.1%/1000 h for more than 30 000 as systems). Degradation of stacks that have been designed for application in small residential cogeneration or in transportation, however, exhibits different features mainly because of differences in materials used and stack design of such new applications. This article describes the characteristic features of degradation from cell to stack levels. Finally, to obtain full understanding of degradation and to establish a well‐designed solid oxide fuel cells (SOFC) control system, there is a discussion on what is to be realized and what is to be overcome.
Impact of impurities on reliability of materials in solid oxide fuel cell (SOFC) stack/modules
Authors: Yokokawa H. , Sakai N. , Horita T. , Yamaji K. 
Published: December 2010

AbstractThe impurity behavior in solid oxide fuel cells is discussed in terms of the thermodynamic characteristic properties in particular on the basis of acid–base concept in theoretical consideration and in terms of actually observed quantities of impurities with SIMS techniques. The thermochemical stability of cathodes can be represented in the chemical potential diagrams where the thermodynamic activity of basic oxides (SrO, La2O3) are used. By adopting the same axes, this makes it possible to compare thermodynamic properties for different elements in the La–Sr–M–O system (M = elements). By using this diagram, the acidity of respective impurity elements are defined and compared with the main transition metal element in cathode materials. The impurity behavior inside SOFC stacks is also examined by using the diagram with temperature and oxygen potential axes. This makes it possible to see the interaction of the cell component with impurities as functions of temperature and oxygen potentials. Examples are given for Ni–S–O–H system. Finally, the impurity behavior in actual stacks detected by SIMS was examined and compared with thermodynamic prediction with the emphasis on the interaction between impurities and the main component as functions of fuel utilization and other fuel cell conditions.