bluuebunny/crossref_metadata_2025_split huggingface dataset:
Alternative design possibilities for integrated fuel processors
Authors: Voecks G. E. 
Published: December 2010

Abstract
The majority of fuel processors that have been developed to support proton exchange membrane (PEM) fuel cells have basically been adaptations of largescale commercial processes and designs. This has been largely a result of the combined engineering familiarity of industrial hydrogen production and purification practices, and the evolution of these techniques over the past 30 years as they have developed for the anticipated commercial fuel cell systems' uses. Alternative conversion processes for various fuels, employing technologies not widely practised industrially or designs not previously integrated with fuel cells may offer PEM fuel cell systems certain advantages as they are developed for various applications, including transportation. A review of three different technological approaches that offer unique possibilities are examined for consideration as PEM fuel cell systems continue their development. The technical examples discussed are not intended to be exhaustive but rather chosen to be illustrative of the technology presented.
Well‐to‐wheel efficiencies of different fuel choices
Authors: Höhlein B. , Isenberg G. , Edinger R. , Grube T. 
Published: December 2010

AbstractIn order to assess a future fuel supply, it will be necessary to define and establish energy, emission and cost balances from the primary energy at the source or well up to the final energy carrier (fuel) at the filling station. In addition to vehicles with internal combustion engines, it will be necessary to give consideration to hybrid vehicles, battery‐powered and fuel cell‐powered electric vehicles supplied with fuels produced from both fossil and renewable resources. Overall balances (well‐to‐wheels) including fuel supply (well‐to‐tank) and the use of vehicles (tank‐to‐wheels) in terms of energy, emissions and costs are necessary.
Basic materials corrosion issues
Authors: Shores D. A. , Deluga G. A. 
Published: December 2010

AbstractThe use of corrosion tests that appropriately simulate the environment in the proton exchange membrane fuel cell (PEMFC) is discussed. Caution is advised in the interpretation of electrochemical corrosion tests. Metallic bi‐polar plates typically achieve corrosion resistance by forming passive oxide films, which must be sufficiently conductive to allow high fuel cell current densities. Austenitic stainless steels are obvious candidate alloys. The key issue with regard to corrosion is that the alloy selected should exhibit passive behavior in its local chemical environment and at the electrochemical potentials imposed upon it by the anode or cathode.Different corrosion tests will yield differing corrosion rates of a given alloy for various reasons: (a), the test measures the corrosion rate at the alloy's natural corrosion potential rather than at an imposed potential; (b), insufficient exposure time was allowed for the alloy to fully develop its passive film; (c), other oxidation or reduction reactions may operate in parallel with the corrosion reactions, which will invalidate the inference of a corrosion rate from a measured net current density.Therefore, out‐of‐cell corrosion tests should be checked for self‐consistency. Corrosion rates are typically slower in the cathode‐simulating conditions than in anode conditions. Anode‐side corrosion rates are predicted to be higher at low fuel cell power, but cathode‐side corrosion rates are likely to be insensitive to power levels.A good, commercial grade stainless steel is unlikely to suffer perforation or collapse of the bi‐polar plate within the design lifetime, but other corrosion‐related failure modes may become important. Two of these are an increase in contact resistance and the release of corrosion product cations, which can reduce the conductivity of the membrane. A simple model was used to illustrate how the reduction of membrane conductivity was dependent upon corrosion rate and fuel cell power.
Metal bipolar plates and coatings
Authors: Wind J. , LaCroix A. , Braeuninger S. , Hedrich P. , Heller C. , Schudy M. 
Published: December 2010

AbstractThe use of metals as a material for bipolar plates in proton exchange membrane (PEM) fuel cells offer a number of advantages in comparison with other materials. Several companies and institutes are currently working on the development of such bipolar plates and have patented their results. Whereas in the production of metallic bipolar plates there are no major obstacles, there are still some issues to be solved concerning corrosion and conductivity of these plates in the fuel cell environment. Up to now, the method of solving these issues seems to be to coat the plates with materials which prevent corrosion and growth of oxide layers with a high resistivity. The requirements for these bipolar plates and their current status is outlined in the chapter.
Interdigitated flow field design
Authors: Nguyen T. V. , He W. 
Published: December 2010

Abstract
When interdigitated gas distributors are used in a proton exchange membrane fuel cell (PEMFC), fluids entering the fuel cell are forced to flow through the electrode porous backing layers. This through‐the‐electrode convection increases the transport rates of the reactants and products to and from the catalyst layers, and the shear force of gas flow minimizes electrode flooding by reducing the amount of liquid water that is entrapped in the porous electrodes. To investigate the effects of the gas and liquid water hydrodynamics on the performance of an air cathode of a PEMFC employing an interdigitated gas distributor, a two‐dimensional, two‐phase, multi‐component transport model was developed. The predictive capability of the model was validated against experimental results obtained at multiple operating conditions. The model was also used to investigate the effects of two flow field design parameters on the cathode performance.
Two–phase flow and transport
Authors: Wang C.‐Y. 
Published: December 2010

Abstract
This chapter reviews latest experimental and modeling efforts towards developing a basic understanding of two‐phase flow physics in proton exchange membrane fuel cells. Both hydrogen proton exchange membrane fuel cells and proton exchange membrane based direct methanol fuel cells are discussed. As an important example of materials characterization, wetting characteristics of gas diffusion layers are examined and the techniques of measuring contact angle are discussed. Next, a comprehensive physico‐chemical modeling framework of combining electrochemistry with two‐phase transport is presented along with select numerical examples for both hydrogen and direct methanol fuel cells. The current state of the computational efficiency of these comprehensive models is indicated. A critical need for model validation against detailed data of the current distribution is demonstrated, and a new technique of measuring the current distribution using a segmented flow plate and a multi‐channel potentiostat is presented. Finally, areas for future research into two‐phase transport in proton exchange membrane fuel cells and the associated cathode flooding are pointed out.
First principles modeling of sulfonic acid based ionomer membranes
Authors: Paddison S. J. 
Published: December 2010

Abstract

Proton dissociation in the sulfonic acid groups of hydrated Nafion
®
and polyetherketone membranes along with its connection to proton transport within the membrane pores is discussed. Minimum energy conformations for trifluoromethane and
para
‐toluene sulfonic acids with clusters of 1–6 water molecules were obtained using ab initio electronic structure calculations. These calculations revealed the influence of both the structure and strength of the conjugate base (sulfonate anion) on the dissociation and hydration of the acid. Although spontaneous dissociation was observed for both sulfonic acids after the addition of three water molecules, the proton (as a hydronium ion) is less bound for the perfluorinated system than with the aromatic system. This is due to the increased electron stabilization afforded by the electron withdrawing of the CF
3
group. This molecular membrane specific information was used in combination with membrane morphology data to compute proton diffusion coefficients for both Nafion 117 and 65% sulfonated polyetherketone membranes at hydration levels where the number of water molecules per sulfonic acid fixed site were: 6, 13, and 22.5; and 15, 23, and 30, respectively. The agreement with pulsed field gradient NMR diffusion measurements was very good for both membranes across the entire range of membrane hydration, attesting to the substantial predictive capability of the transport model.
Composite perfluorinate membranes
Authors: Nakao M. , Yoshitake M. 
Published: December 2010

AbstractAs typical composite perfluorinated membranes applied to proton exchange membrane fuel cells, two types of membranes with different reinforcements are reviewed, focusing on their preparation methods, mechanical and electrochemical properties.One is Gore‐select®which is reinforced with a porous polytetrafluoroethylene (PTFE) sheet. The thin membrane is prepared by impregnating a solution of perfluorinated ionomer into a thin PTFE porous sheet. The other is PTFE micro‐fibril reinforced membrane. The thin membrane is prepared by stretching a thicker composite film. Compared with non‐reinforced membranes, the composite membranes have many advantages both in mechanical properties and in electrochemical performance.
Hydrocarbon membranes
Authors: Kreuer K. D. 
Published: December 2010

Abstract

The preparation of sulfonated hydrocarbon based membranes is described and the properties relevant for polymer electrolyte membrane fuel cell applications are discussed in relation to their typical chemical and microstructural features. Especially sulfonated high performance polyarylene membranes combine good durability with high proton conductivity (in the wet state), making them interesting low‐cost alternatives for perfluorosulfonic acid polymer membranes (e.g., Nafion
®
). The sharp decrease in conductivity with decreasing water content as a direct consequence of the inherently lower acidity and nano‐separation is partially compensated by fewer humidification problems as a result of lower electroosmotic drag. The poorer mechanical properties (brittleness in the dry state and increasing softness in the wet state) have been improved by blending and/or crosslinking. An interesting perspective for liquid direct methanol fuel cell applications, which require low methanol cross‐over, is provided by the lower electroosmotic drag of water and methanol observed at moderate temperatures (>60 °C) and low methanol concentrations. But the generally high swelling in water/methanol mixtures especially at higher temperatures is currently preventing hydrocarbon based membranes from being used in direct methanol fuel cells. While proton and water transport are generally related in conventional membranes, pure proton conductivity in low humidity environment at higher temperature may be achieved with heterocycles (e.g., imidazole) as proton solvent in fully polymeric systems.
High–temperature membranes
Authors: Wainright J. S. , Litt M. H. , Savinell R. F. 
Published: December 2010

AbstractA review is presented of work in the area of polymer electrolyte membranes for fuel cell operation at temperatures exceeding 100 °C. Development of these electrolytes will permit fuel cell operation with greatly increased tolerance to carbon monoxide, and greatly reduced humidification requirements. The focus is on the electrolyte membranes based on basic polymers doped with acids, i.e., phosphoric acid‐doped polybenzimidazole. The key properties of these membranes including conductivity, permeability, and mechanical strength are reviewed, as well as fuel cell performance under various operating conditions.
Membrane/electrode additives for low–humidification operation
Authors: Lin J.‐C. , Kunz H. R. , Fenton J. M. 
Published: December 2010

AbstractProton exchange membrane fuel cells are limited in their potential for commercialization, since a high water content is required in the Nafion®ionomer currently used as the electrolyte. Research is currently being performed to reduce this water requirement while still maintaining high ionic conductivity. One approach that shows promise incorporates solid proton conductors such as phosphotungstic acid or zirconium (hydrogen) phosphate into the ionomer. Operating at low water content in the membrane allows cell operation at higher temperatures without cell pressurization. Higher temperature operation improves the performance of the cell, reduces the cost of the fuel cell power plant, and makes the proton exchange membrane fuel cell more attractive for the direct use of methanol as the fuel. This section presents a survey of approaches that have been used and experimental data showing the current status of performance of proton exchange membrane fuel cells operating with low water content.
High dispersion catalysts including novel carbon supports
Authors: Tada T. 
Published: December 2010

Abstract
Pt catalysts and PtRu catalysts supported on conductive carbon black (catalyst loading is from 10 wt% to 60 wt%) are normally used for proton exchange membrane fuel cells, since supported catalysts have higher active surface area than nonsupported catalysts because of uniform dispersion and smaller particles. Also, supported catalysts are more stable concerning catalyst agglomeration than nonsupported catalysts during fuel cell operation. In the case of Pt catalyst, the effect of carbon support on the catalyst's characterization and catalytic activity of the oxygen reduction reaction are investigated. The effect of metal loading on the catalytic activity of the oxygen reduction reaction is also discussed. In the case of PtRu catalyst, the influence of carbon support and metal loading on the catalyst's characterization and the CO tolerance of the catalysts are investigated. The effect of operating conditions and electrode structure on CO tolerance of the PtRu catalyst's anode are also discussed. Moreover, catalyst agglomeration phenomenon of Pt catalyst and degradation of CO tolerance of PtRu catalyst after fuel cell operation are investigated.
Principles ofMEApreparation
Authors: Kocha S. S. 
Published: December 2010

AbstractA brief history of the evolution of the fuel cell electrode, emphasizing the technological developments that have lead to the contemporary polymer electrolyte membrane electrode assembly (MEA). This is followed by a discussion of the requirements, functions and properties of individual components and processes by which they are fabricated into MEAs. Lastly, basic in situ electrochemical techniques that may be applied as diagnostic tools to understand and advance the performance of MEA technology are reviewed.
Novel catalysts, catalysts support and catalysts coated membrane methods
Authors: Debe M. K. 
Published: December 2010

Abstract

This chapter introduces a new type of catalyst electrode for proton exchange membrane (PEM) fuel cells based on a nanostructured thin film catalyst support system. The nanostructured film consists of a single layer of a dense distribution of oriented crystalline whiskers of an organic pigment material. With areal number densities of 3–5 billion cm
−2
and micrometer scale lengths, using dry processes, the whiskers are grown, coated uniformly with catalysts and transferred to the surface of a PEM to form an electrode. The physical and chemical properties of the nanostructured supports are reviewed first, followed by properties of the catalyst coatings and finally the electrode layer formation. Differences of these characteristics and properties from conventional carbon particle supported dispersed catalysts are widely made. Fuel cell performance examples and comparisons contrasting the mass and area cathode specific activities of the two types of catalyst electrode systems are demonstrated. The differences have implications for how membrane electrode assembly (MEA) are fabricated, ultimate catalyst loadings, system humidification requirements and durability.
Beginning‐of‐lifeMEAperformance — efficiency loss contributions
Authors: Gasteiger H. A. , Gu W. , Makharia R. , Mathias M. F. , Sompalli B. 
Published: December 2010

AbstractBeginning‐of‐life H2‐fed fuel cell performance of membrane electrode assemblies (MEA) made using state‐of‐the‐art subcomponents (25–50 µm membranes, 47 wt% Pt on carbon, 0.15–0.4 mg cm−2Pt cathode loading, ≤1100 equivalent weight (EW) ionomer/binder) was studied. Performance data were taken using small‐scale (50 cm2) cells and a large‐scale (500 cm2, 22 cell) stack, and voltages were corrected for membrane resistance in order to isolate cathode polarization losses. Based on catalyst and MEA cyclic voltammetry and in‐situ testing with pure O2feed, we observed loading independent O2kinetic control up to 1.8 A cm−2at 80 °C under fully humidified conditions; this indicates negligible effects of cathode layer proton transport limitations with pure O2. With air as the oxidant, we observed O2kinetic control below 0.2 A cm−2and the onset of O2transport resistances at higher current densities. Results with helox (21% O2in helium) as the cathode feed revealed that the O2transport resistances were roughly evenly distributed between gas and solid phases. With incomplete reactant humidification, additional membrane resistance was observed and proton conductivity losses in the cathode layer became significant. Moreover, thin (25 µm) low‐equivalent weight (EW) MEAs outperformed thicker (50 µm) high EW MEAs even after correcting for membrane ohmic losses. This is due to faster water transport of the thinner low EW MEAs resulting in improved retention of cathode layer proton conductivity under dry conditions.
Effect of ionic contaminants
Authors: Okada T. 
Published: December 2010

Abstract

In polymer electrolyte membrane (PEM) fuel cells, the electrolyte membrane is easily contaminated by foreign cations because of a higher affinity of these cations with the sulfonic acid group than that of H
+
. Thereby three modes of degradation in the membrane which affect fuel cell performance are anticipated. The first is a direct effect, and comes from alteration of the membrane bulk properties, e.g., lowering of membrane ionic conductivity, water content, H
+
transference number. This effect is normally not so serious unless the membrane is severely contaminated. The second comes from the altered water flux inside the membrane, owing to the terms of electroosmotic drag and diffusion coefficient of water affected by the presence of contaminant ions. This results in membrane drying and lowering of membrane conductivity. The degradation starts when the contaminant level exceeds 5%. Simulation results concerning the water concentration profile, membrane ohmic resistance and membrane overpotential are presented based on water flux equations derived using experimentally obtained transport parameters. The last effect comes from the degradation of the cathode catalyst due to the presence of contaminant ions at the interface between the platinum catalyst and the ionomer layer. This effect is the most serious as regards the fuel cell performance, because a contaminant level as low as 1% is enough to come into effect. Membrane contamination by foreign cations, especially local contamination at the cathode catalyst layer, deteriorates the fuel cell performance significantly, and needs special caution in fuel cell design.
Reliability issues and voltage degradation
Authors: Fowler M. , Mann R. F. , Amphlett J. C. , Peppley B. A. , Roberge P. R. 
Published: December 2010

AbstractTo date the application of fuel cell systems has focused on operational performance and little attention has been given to the reliability of fuel cells and stacks. This section discusses reliability and system effectiveness as they are related to fuel cell stacks, with a specific focus on proton exchange membrane (PEM) fuel cell stacks. The potential applications of different reliability analysis methodologies to fuel cell stacks is discussed. The potential failure modes and causes of failure experienced in fuel cells stacks are outlined. There are a number of reliability analysis techniques practiced today that would be useful in the further development of fuel cell stacks. This section briefly introduces these techniques and the information and data requirements of each technique. The three basic techniques to be addressed include: failure mode and effects analysis, reliability block diagrams and fault tree analysis. Durability or irreversible degradation of the stack is defined as the ability of a membrane and electrode assembly (MEA) to resist permanent change in performance over time. With respect to fuel cell stacks, the definitions for reliability of the stack include failure modes that can lead to catastrophic failure, as well as performance degradation to below an acceptable level. Stability or reversible degradation are the recoverable phenomena involving voltage or current density decay. The application of reliability terminology for fuel cell stacks is addressed, and different definitions for failure are discussed. Causes of PEM fuel cell failure are likely to be defect propagation, low level contamination, corrosion of the plates leading to increased contact resistance, thermal or hydration cycling leading to mechanical stress, catalyst particle ripening, swelling of polymer materials in the active catalyst layer leading to changes in water removal characteristics, compaction of the gas diffusion layer due to mechanical stresses, degradation of the polymer material and surface chemistry changes in gas diffusion layer.
Air‐supply components
Authors: Pischinger S. , Lang O. 
Published: December 2010

AbstractThe careful layout of air‐supply systems is a key parameter to achieve high overall efficiencies of PEM fuel cell applications. This part of the system determines the humidification concept as well as pressure level and power density, respectively. This chapter describes the basic requirements which must be taken into account during the layout of a PEM fuel cell system. The thermodynamic fundamentals of compressor and expander units are explained and examples of practical units are shown. Furthermore, acoustic aspects are discussed and the influence on the humidification concept is discussed. Finally, a simulation tool is presented which supports the user in the layout of the overall system and represents a hardware‐in‐the‐loop environment. This tool supports component developments under steady‐state and transient boundary conditions so that control algorithms can be developed.