bluuebunny/crossref_metadata_2025 huggingface dataset:
Catalyst development for water–gas shift
Authors: Ladebeck J. R. , Wagner J. P.
Published: December 2010

In the industrial production of hydrogen and of synthesis gas the water gas shift reaction represents an essential step for the overall process efficiency of the process by increasing the hydrogen yield and by adjusting the desired ratio of hydrogen and carbon monoxide for a subsequent synthesis step. In addition to that in fuel cell technology it is absolutely necessary to decrease the CO content of the fuel hydrogen due to the limited CO tolerance of present day fuel cell anodes. To be successful applying water gas shift catalysts in hydrogen production for fuel cells especially in automotive systems some major obstacles of the commercial Cu/Zn/Al catalyst systems must be overcome. Major new demands are reduction of volume and weight by two to three orders of magnitude, oxidation resistance and improved tolerance for steam condensation and poisons, here mainly sulfur present in gas feedstock and in gasoline. Precious metal catalyst systems on rare earth metal oxides are most promising and could fulfill the requirements in nonstationary applications were conventional catalysts are not applicable.
PROXcatalysts
Authors: Shore L. , Farrauto R. J.
Published: December 2010

The proton exchange membrane fuel cell uses a Pt‐based catalytic anode and operates at about 80 °C. The hydrogen that is oxidized at the fuel cell anode can be obtained from reforming a hydrocarbon fuel. Depending on the reforming model, the hydrogen stream may initially contain almost 10% CO (dry basis). Since carbon monoxide adsorbs strongly on precious metals, one of the most important requirements for successful operation of this fuel cell is that the CO concentration be reduced to <10 ppm (99.99% conversion) to protect the Pt anode from CO poisoning and deactivation.

The task of CO removal is a multi‐stage process within the fuel reformer. The primary CO converter is a water gas shift (WGS) reactor, where the CO is reacted with water to yield equimolar concentrations of CO2and H2. Because of both thermodynamic and kinetic limitations, WGS normally yields a stream with 0.2–0.5% CO. The most effective mechanism for further CO removal is oxidation with air injection. Because of the very high ratio of hydrogen to carbon monoxide (>100 : 1), the catalyst needs to be highly selective. Therefore, the process is called selective oxidation or preferential oxidation (PROX).

The objective of the PROX reaction is high CO conversion to CO2without excessive hydrogen oxidation (to water). This article discusses the details of the PROX reaction, catalytic materials currently being investigated and alternative approaches to CO removal.
Hydrogen safety, codes and standards for vehicles and stationary applications
Authors: Scheffler G. , Wurster R. , Schindler J.
Published: December 2010

General safety characteristics and considerations of hydrogen systems are presented herein as they relate to fuel cell power generators.

The use of hydrogen in “town gas” dates back to the 1800s. From these early applications to current industrial and aerospace uses, an excellent safety record has been established with hydrogen. As we move forward towards new applications, it is essential that the developers of new equipment recognize the practices currently used by the hydrogen industry and adapt these practices to the development of new products. This article describes design processes and work practices required for the safe operation of hydrogen systems. Furthermore, relevant codes, standards and regulations are compiled and discussed from both North American and European perspectives.

In North America, standards already exist for industrial hydrogen systems and stationary fuel cell power plants. These standards are being revised to expand applicability and new standards are being written for new products, such as fuel cell powered vehicles and portables. Additionally, codes, standards and regulations are being developed to address the installation of hydrogen systems and fuel cell power plants.

Among the regulations and standards addressed from the European perspective are the International Organization for Standardization the International Electrotechnical Commission, European Commission Council Directives and European Accord Europeen Relatif au Transport International des Marchandises Dangereuses Par Route (ADR) regulations.

For vehicles and related infrastructure systems and components different regulations or standards are applicable. In North America, self‐certification is the standard procedure to bring vehicles on public roads, whereas in Europe, a whole vehicle type approval is performed either on the basis of an European Economic Community directive or an Economic Commission for Europe regulation, not based on any standards. For the future harmonized certification of hydrogen road vehicles in Europe, work initiated by the European Integrated Hydrogen Project are addressed.

For the approval of stationary hydrogen systems and components, as an example, German jurisdiction and permission procedures for hydrogen refueling stations, the applicable pressure vessel regulations, the type approval and recurrent testing are explained as required instruments.
Graphite–based bipolar plates
Authors: Roßberg K. , Trapp V.
Published: December 2010

Composites of polymer binders and conductive particles (e.g., graphite powder) are an interesting alternative bipolar plate material, since they are less expensive than pure graphite and less corrosion‐sensitive than metals. By appropriate choice of both components these composite materials can be tailored to meet the requirements of good high‐volume processability (e.g., by injection‐molding) and adequate behavior under fuel cell operation. Another graphite‐based bipolar plate material is graphite foil which is obtained by pressing expanded natural graphite. Both graphite based bipolar plate materials described in this chapter can be considered as “specialists” for different fuel cell applications. Graphite foil is especially attractive for lightweight fuel cell applications, e.g., in the portable and automotive field. For both kinds of bipolar plates, material issues are discussed and the processing technologies are described. Furthermore, techniques to reduce the contact resistance of molded graphite/polymer composite bipolar plates and to increase the gas‐tightness of graphite foil are indicated. The strong influence of the specifications of the starting materials and the processing conditions on the product quality is pointed out.
Ptalloys as oxygen reduction catalysts
Authors: Thompsett D.
Published: December 2010

The use of carbon‐supported Pt alloy catalysts for phosphoric acid fuel cells (PAFC) is well established. In comparison with Pt‐only catalysts, Pt alloy catalysts offer greater oxygen reduction activity and durability. In contrast, the introduction of Pt alloy catalysts for proton exchange membrane fuel cells (PEMFC) is in its infancy, despite having been shown to offer better performance to Pt‐only catalysts. Since the first reports of the use of Pt alloys as cathode catalysts in PEMFCs in 1992, surprisingly little further work has been reported. However, carbon‐supported Pt alloys have been shown to give superior performance to Pt in practical fuel cell hardware, as well as showing good durability. The mechanisms for enhanced activity of Pt alloys for oxygen reduction have been debated for the last 20 years, with many ideas proposed. However, more recently, the use of in situ characterization techniques, especially X‐ray adsorption spectroscopy, has shed light on the differences between Pt and Pt alloys at the potentials of oxygen reduction. It has been shown that alloys show differences in electronic and structural properties, as well as inhibited chemisorption of oxygenated species and stability of surfaces to reconstruction.
Manufacture of electrocatalyst powders by a spray‐based production platform
Authors: Hampden‐Smith M. , Atanassova P. , Atanassov P. , Kodas T.
Published: December 2010

This chapter describes a spray‐based method to manufacture electrocatalyst powders for fuel cell and related applications. The attributes of this process are compared to traditional solution precipitation/impregnation methods as well as non‐powder‐based electrocatalyst production methods. The spray‐based process described here results in formation of unique spherical, micrometer‐sized aggregates consisting of sub‐micrometer electrocatalyst particles where the nanometer sized active phases (Pt, PtRu, metal alloys, metal oxides, composite and anchored molecular compounds) are highly dispersed on the surface of carbon supports. The advantages of this method to manufacture electrocatalyst powders are described in terms of process economics and performance.
Mechanisms of membrane degradation
Authors: LaConti A. B. , Hamdan M. , McDonald R. C.
Published: December 2010

Introduction of proton‐exchange membranes as solid electrolytes has permitted the development of fuel cells that utilize hydrogen, reformate gas and methanol as reactants. Modern fuel cells have extended service life and reliability and increased power and energy density. The need for fuel cell operating in excess of 5000 h for transportation and 30 000 h for stationary applications has led to extensive investigations of the failure modes in an effort to understand the primary mechanical, chemical and electrochemical mechanisms. This chapter reviews the progress in understanding the limitations of fuel cell operation with historical and current state‐of‐the‐art membranes and suggests directions for achieving further improvement.
System design for vehicle applications:GM/opel
Authors: Masten D. A. , Bosco A. D.
Published: December 2010

Polymer electrolyte membrane fuel cells (PEMFCs) offer the promise of low or emissions‐free, high efficiency vehicle power trains. However, many challenges and trade‐offs are inherent in the adoption of the PEMFC stack to a complete production automotive system. In this chapter, major vehicle requirements are considered. A brief survey of the characteristics of direct hydrogen fuel cell systems, some permutations to the basic system and the options available to a system designer, as well as a more detailed discussion of some of the key trade‐offs, are presented.
Special applications usingPEM‐technology
Authors: LaConti A. B. , Swette L.
Published: December 2010

Proton‐exchange or polymer electrolyte membrane (PEM) water electrolyzers, because of their superior performance reliability and long life, have been selected for use for advanced Navy and NASA oxygen life‐support applications. Some of the characteristics of PEM electrolyzers using liquid water anode or cathode feeds, as well as water vapor cathode feeds, are described. There has also been significant progress in the development of high‐energy‐density regenerative PEM fuel cells for NASA space and high‐altitude, solar‐powered aircraft applications. Small PEM electrolyzers that supply up to 1200 cm3H2 min−1have been sold commercially for over 25 years to replace gas cylinders and supply high‐purity hydrogen in laboratories and in the field for flame ionization detector‐based gas chromatographic applications. Also, larger PEM electrolyzers ranging from 1 m3H2 h−1to 20 m3H2 h−1have been sold commercially for cylinder replacement and on‐site hydrogen generation applications such as electrical generator cooling, electronic and metal processing and corrosion prevention. Recent emphasis has been on development of advanced water electrolyzers that generate hydrogen for storage at elevated pressure (up to 17.2 MPa) and oxygen at near‐ambient pressure. These advanced electrolyzers do not require a separate high‐pressure gas containment vessel or high‐pressure liquid water feed pump. Possible alternative applications of this technology are in the fuel cell and related fields for energy storage, power backup, power boosting and refueling. The extension of the above PEM technologies to some electrochemical gas concentrator/compressor applications is reviewed.
Transport/kinetic limitations and efficiency losses
Authors: Müller J. , Frank G. , Colbow K. , Wilkinson D.
Published: December 2010

The following contribution explores many of the fundamental aspects of the direct methanol fuel cell (DMFC). In particular, the electrochemical and physical processes that occur in the unit cell and the techniques used to study these phenomena are discussed. This information leads to a clearer picture of the breakdown and relative importance of the various contributions to the overall efficiency loss in a DMFC. The short introduction provides a brief perspective on the historical development of the DMFC and compares the present day performance to the conventional hydrogen/air fuel cell. A discussion of some of the analytical tools used to study the DMFC and probe the various processes, particularly under automotive operating conditions, follows. Techniques such as a.c. impedance spectroscopy under operating load conditions and gas chromatography for measuring methanol and carbon dioxide crossover, will be discussed in detail. The unit cell processes that typically dominate the performance characteristics of a DMFC under automotive operating conditions include: kinetic limitations at the anode and to a lesser extent at the cathode, mass transport limitations at the cathode and methanol and water crossover through the membrane from the anode to the cathode. By quantifying the various cell processes occurring by considering the overall mass flow and material balance, a more complete quantitative picture of the performance limitations of the DMFC expressed in terms of the relative contributions of the efficiency losses can be formulated. The contributions of the anode and cathode to the total efficiency losses are roughly comparable, unlike hydrogen/air fuel cells. Finally, in conclusion, this contribution will summarize some of the key findings and provide an outlook to the future.
New materials for
DMFC
MEAs
Authors: Neergat M. , Friedrich K. A. , Stimming U.
Published: December 2010

In recent years, the progress in the development of direct methanol fuel cells (DMFCs) for various applications has been enormous. It is probable that DMFC systems will soon be available as commercial products, especially in the low power range (<100 W). The materials currently used are, however, not optimized for the DMFC application. With this contribution we focus on the material aspects of the “active” components of the membrane electrode assembly (MEA). These components are the catalysts for the anode and cathode, the polymer membrane electrolyte and the diffusion layers. However, material issues regarding bipolar plates and other components of a stack are also discussed at the end of the review. After an introduction in which the basic concepts and processes of DMFCs are portrayed the main issues in DMFC development are discussed. Next, the specific demands that the materials must fulfil in DMFCs are presented. A discussion of the recent developments in membrane research and development follows, which is the crucial component regarding the goal to improve DMFC performance and fuel utilization. Therefore, we have devoted a considerable part of the chapter to this issue of new membrane materials. The catalysts and their reactivity are also an important issue in DMFC development. Both anode and cathode activities are crucial; we discuss mainly the systems that are already being used in MEAs. General considerations follow regarding electrode structure, catalyst utilization and porosity of the electrode. We also show in this contribution that besides the properties of the materials, the electrode structure also has a major influence on the processes in DMFCs.
DMFCsystem design for portable applications
Authors: Narayanan S. R. , Valdez T. I. , Rohatgi N.
Published: December 2010

Direct methanol fuel cells (DMFCs) in portable applications are expected to provide substantially higher energy density and longer operating times over advanced batteries. The time threshold of advantage of using a fuel cell instead of a battery is almost independent of the power level, and is determined by the power density of the fuel cell and its operating efficiency. The various requirements for portable fuel cells that determine system design are defined with examples. The system design process and analysis methods are illustrated. The characteristics of cells and stacks required for system design are described. The dependence of DMFC stack performance on airflow rate, methanol concentration and temperature are necessary for developing closed loop mathematical models for system design. Such a closed loop system model has been developed and the consequences of varying airflow rate on water recovery, thermal management and overall system performance have been analyzed. Using this model, the effect of crossover rate on the overall efficiency, power density and the operating methanol concentrations have also been investigated. Effect of components on the overall power budget and design issues relating to start‐up and transient response are also discussed.
Electrolyte and material challenges
Authors: Hoffmann J. , Yuh C.‐Y. , Godula Jopek A.
Published: December 2010

This chapter sets its focus on the properties of known electrolytes as well as on new improved approaches. So far, most developers have favored two electrolyte mixtures, the lithium potassium carbonate (Li/K 62 : 38 mol%) and the lithium sodium carbonate (Li/Na 52 : 48 or 60 : 40 mol%). The published properties of these mixtures, in spite of the fact that many of them have been measured under different experimental conditions, are compared and discussed. The molten carbonate fuel cell (MCFC) community is separated into two main groups, which differ mainly in the gas compositions and utilization applied. Since the properties of the electrolyte are influenced significantly by these operating conditions, the electrolyte itself, which is in contact with most of the cell components, may also vary in how it interacts with the components. Therefore, the corrosion of the hardware material (bipolar plate, current collectors, electrodes, matrix, internal reforming catalyst), the evaporation of the electrolyte components and finally the electrochemical properties depend on the operation conditions and have a significant influence on the performance and lifetime of carbonate fuel cell systems. Experimental observations describing effects arising from interaction of the electrolyte with other components are also discussed in this chapter.
System design
Authors: Farooque M. , Ghezel‐Ayagh H.
Published: December 2010

Carbonate fuel cell systems promise to provide high efficiency ultra‐clean power generation from a variety of gaseous, liquid and solid carbonaceous fuels. Designs of power generation units have been developed for natural gas, biogas, coal, ethanol and petroleum distillate fuels. The carbonate fuel cell, because of its high operating temperature (550–700 °C), allows significant system simplification by integrating the internal reforming feature into the fuel cell stack as well as use of the by‐product heat in an efficient bottoming cycle. Simple cycle sub‐megawatt and MW class natural gas systems promising efficiencies of 45–60% lowest heat value (LHV) are being developed for distributed power generation applications. Natural gas‐fueled power plant concepts with efficiencies over 70% (LHV) have also been developed using carbonate fuel cells integrated with gas turbines. The carbonate fuel cell system promises unique efficiency advantages with high carbon dioxide containing medium and low Btu fuels such as coal gas and biogas. This is in lieu of carbon dioxide being a reactant in carbonates fuel cells as opposed to other types of fuel cells. This advantage coupled with internal reforming capability allows configuration of high efficiency power plant systems based on the carbonate fuel cell.
Durability
Authors: Fujita Y.
Published: December 2010

This paper considers the dominant factors of performance decay of molten carbonate fuel cell (MCFC) stacks. Single cell operation results and the post‐test analysis are discussed, and recent approaches to achieve lower decay rates and longer operation times are described. The decay rate of 1 m2class stacks is analyzed based on single cell data. The life‐limiting factors and the analysis of the decay rate are discussed based on results of stacks with conventional components, which are Ni/Al oxide dispersed strengthen anodes, in situ oxidized NiO cathodes, γ‐LiAlO2matrices with (Li0.62.K0.38)2CO3electrolyte and AISI316L multiple cathode current collectors (perforated plate + corrugated plate). To achieve 40 000 h operation, there were three dominant factors controlling the life and the decay. These factors were the electrolyte loss, the Ni dissolution and the particle growth of LiAlO2. The reduction of the metallic surface area of the cathode current collectors, (Li/Na)2CO3electrolyte and the α‐LiAlO2particles with uniform diameter distribution were examples of the countermeasures and showed good prospects for extending the life of MCFC.
Current electrolytes and catalysts
Authors: Kawada T. , Mizusaki J.
Published: December 2010

Stabilized zirconia (ZrO
2
) is recognized as the major candidate for the electrolyte material of solid oxide fuel cells (SOFCs) owing to its high ionic conductivity and chemical stability. The ionic conductivity originates from the oxygen vacancies introduced by doping 2+ or 3+ valence cations on the Zr
4+
site. The conductivity shows the maximum at a certain dopant concentration. Although stabilized zirconia is a dominantly ionic conductor, electronic conductivity is not completely zero. Taking into account both the ionic and the electronic conductivities, the optimum electrolyte thickness is calculated to be 10–100 µm when the current density of 0.1–1 A cm
−2
is generated at 1000 °C.

Electrode materials should have high catalytic activity, high electronic conductivity, and high chemical and morphological stability. Currently, (La,Sr)MnO
3
and Ni–YSZ cermet are the most popular cathode and anode, respectively. The crystal lattice of (La,Sr)MnO
3
has a distorted perovskite type structure. The symmetry varies with oxygen partial pressure and temperature. Electrical conductivity of La

1−
x

Sr

x

MnO
3
(x = 0–0.4) ranges from 100 to 300 S cm
−1
at 1000 °C in air. Oxygen diffusion coefficient is 10
−12
 cm
2
 s
−1
, which is not enough to supply oxygen via the electrode bulk diffusion. Although catalytic activity is lower than a mixed conductor oxides such as (La,Sr)CoO
3
, (La,Sr)MnO
3
has higher compatibility with YSZ electrolyte. Nickel is a superior catalyst for the electrochemical and chemical reactions when hydrogen or hydrocarbon gases are used as the fuel. The problem with the nickel anode is its morphological instability and thermal expansion mismatch with YSZ. Thus, nickel powders are used in a form of Ni–YSZ cermet. Electrical conductivity of the cermet electrode varies drastically around the percolation threshold. The optimum nickel content is around 40 vol%.

Electrode reaction kinetics has been investigated intensively for the cathode and the anode. The major origin of the electrode overvoltage is assumed to be the shift of oxygen potential at the electrode/electrolyte contact, which is caused by the formation of oxygen potential gap or gradient to promote the rate limiting reactions. The current–voltage relationship and the electrochemical impedances are well explained under the assumption, and the reaction models were developed by the reaction order analyses.
MEA/cell preparation methods:Europe/USA
Authors: Stöver D. , Buchkremer H. P. , Huijsmans J. P. P.
Published: December 2010

Cell processing is a key element to providing technical quality and moreover limiting the cost of manufacturing. The processing of cells for solid oxide fuel cells (SOFCs) mostly involves powder technology using suitable methods for the production of bulk as well as layer structured components. The different existing cell concepts and designs are briefly introduced, including tubular and planar types. Methods for the manufacture of substrates and those of layer application are distinguished.

Main tools for substrate processing are warm pressing, extrusion and tape casting. These methods are most commonly used to manufacture tubes (by extrusion) as well as plates or foils; possibly by use of all three methods.

A variety of coating methods is available and applied to build up the different multilayers necessary to make a fuel cell operational. Wet powder spraying is a flexible wet chemical suspension method to apply electrodes, electrolytes and contact layers. It requires the post treatment of sintering. Vacuum slip casting is a very similar method using suspension pouring on a porous substrate and is used for anode and electrolyte deposition. Electrochemical vapor deposition is used for the production of highly dense electrolytes ready for use without any post treatment, however low deposition rates and high temperatures are drawbacks for mass production. The established technique for plasma spraying is also discussed to some detail. However gas tightness for thin electrolytes and coatings on edges might still be a problem. Screen‐printing is also well established in applying ceramic layers on supporting substrates. Electrodes have been produced in various laboratories. Calendaring has been considered, especially as a lamination route to producing complete cells.

Most of the methods need post heat treatments and in order to address the problem of cost reduction, co‐firing steps should be considered. This causes problems of bending and stresses which have to be considered carefully. The chapter closes with some cost considerations of the processes involved.
Interconnects
Authors: Hilpert K. , Quadakkers W. J. , Singheiser L.
Published: December 2010

The interconnect connects the anode side of one single cell with the cathode side of the adjacent single cell, thus preventing the fuel and oxidant gasses from mixing. Ceramic and metallic interconnects are the most widely used concepts. The ceramic interconnect materials used are LaCrO3base perovskites doped with Sr, Ca, or Mg and other metals in order to obtain sufficient electrical conductivity, to modify the thermal expansion, and to improve the sinterability. They are used for tubular cell configurations as well as for the monolithic and planar concepts. Ceramic interconnect materials have shown excellent long‐term behavior for the tubular cells. There is a general trend towards using metallic interconnects in planar cells due to their relatively low costs, easy working potential, as well as high electrical and thermal conductivity. Most developments concentrate on Cr‐based alloys or high‐Cr ferrites depending on the cell design.
Internal reforming
Authors: Eguchi K.
Published: December 2010

In addition to its high conversion efficiency, the solid oxide fuel cell (SOFC) is very attractive from the fuel flexibility point of view. Natural gas has been regarded as the most suitable fuel for the SOFC. Methane, natural gas and hydrocarbons can be readily converted upon direct introduction by a reforming reaction on the Ni/yttria‐stabilized zirconia fuel electrode in the direct internal reforming operation. Internal reforming is attractive not only from the point of view of the simple system, but also the high efficiency due to combined generation with the endothermic reforming reaction. Carbon deposition is one of the damaging factors for the cell for direct internal reforming. The carbon deposition region is determined from thermodynamic equilibrium. Even in the calculated carbon free region, deposition was sometimes observed due to decomposition of hydrocarbon and rapid growth on the Ni catalyst. The selection of the oxide component as well as a metallic component in the cermet should be effective in achieving high performance in the electrode reaction and in avoiding carbon deposition. Stress analysis has been carried out for the internal reforming operation of planar cells. Internal reforming has been successfully carried out in 1 kW planar, several tens of kilowatt scale MOLB type and 10 kW tubular type modules.
System design
Authors: Hartvigsen J. J. , Elangovan S. , Khandkar A. C.
Published: December 2010

Conceptually, a solid oxide fuel cell (SOFC) is an extremely simple solid state device. Cells, comprised of a thin trilayer of electrochemically functional ceramic materials and operating solely by the passage of electrons, oxygen ions and gaseous reactants, may produce a steady source of electric power. In order to insure efficient and durable operation of such cells, careful control of the chemical reactant and thermal energy flows in the cell environment is required. Design of such systems requires the application of such conventional plant design disciplines as heat transfer, fluid mechanics and catalytic reactor design. The SOFC system offers several opportunities to realize economies of operation and construction by integration of system processes and components beyond those normally implemented in conventional unit operation design. Similarly, showing the effects of system design choices on cell operation gives additional direction to the system design. As there are many means of achieving these design objectives, the approach of various SOFC system developers are considered.
New microtube concepts
Authors: Kendall K.
Published: December 2010

Micro‐tubular solid oxide fuel cells (SOFCs) have been developed over the past decade to provide four features which were not thought to be possible in the early 1990s: small SOFC systems from 1 We to 1 kWe; rapid heating systems with start‐up in under 1 min; high power densities near 1 kWe l−1; direct running on a variety of fuels. The main drive for this research emerged as a result of studying extrusion methods for effective fabrication of high quality ceramic membranes, to reveal increased performance combined with extra economy. A further impetus was given by the observation that small tubes of yttria‐stabilized zirconia (YSZ) could resist thermal shocks almost a million times better than flat plate designs. Rapid start‐up of SOFCs thus appeared as a remarkable and new possibility. Such micro‐tubular SOFCs could be used to drive combined heat and power devices to run electronic equipment. Then it became apparent that micro‐tubular cells could run directly on a wide range of fuels, varying from hydrogen, through methane to alcohols to jet fuel and diesel oil. This chapter explains the background and progress of these developments and assesses the potential for further penetration both in technical and application terms.
Direct hydrocarbon
SOFCs
Authors: Barnett S. A.
Published: December 2010

In “direct hydrocarbon” solid oxide fuel cells (SOFCs), the undiluted hydrocarbon fuel is fed directly into the anode compartment, with little or no oxygen‐containing additions (e.g. O
2
, H
2
O, or CO
2
). This can potentially provide the basis for simple, efficient SOFC power plants, and may be an enabling technology for applications such as electricity generation at remote sites, small portable power supplies, and auxiliary power units for vehicles. The main challenge is to develop SOFC anodes that can use hydrocarbons without large overpotentials or carbon deposition. Strategies for electrochemically oxidizing various carbon‐containing fuels without coking are discussed, including reduced operating temperature, alternative anode compositions, and carbon oxidation via electrochemically pumped oxygen. Information currently available regarding the complex reactions of hydrocarbons with typical SOFC anodes is discussed.
Portable
PEM
systems
Authors: Heinzel A. , Hebling C.
Published: December 2010

Fuel cells in the low power range can be operated with either hydrogen or methanol as fuel. Requirements with respect to a hydrogen fuel cell for portable applications are outlined. The state‐of‐the‐art of the development of low power stacks and small‐scale systems is described. Additionally, an overview of the current R&D activities worldwide and of the prototypes presented is summarized, although the reader should be aware of the rapid progress in this type of development. The hydrogen supply to the fuel cell, some properties of hydride materials and data for storage units are considered. The second alternative is to combine the stack with a small‐scale gas processor, and current activities in this sector are described. Finally, a comparison of energy densities of batteries with possible architectures of fuel cell systems is made.
DaimlerChrysler fuel cell activities
Authors: Schmid H.‐P. , Ebner J.
Published: December 2010

This report gives a review of the fuel cell technology used in DaimlerChrysler concept vehicles from 1994 to 2001. The motivation for the strong commitment of DaimlerChrysler in this promising technology is briefly figured out. The basic technical data of all existing fuel cell vehicles of DaimlerChrysler are summarized. Finally, an outlook of ongoing projects, aiming at market preparation is given.
Honda fuel cell activities
Authors: Matsuo S.
Published: December 2010

Honda has demonstrated three types of polymer electrolyte fuel cell systems for vehicles since 1999. The FCX‐V1 was equipped with a metal hydride tank, the V2 with an auto‐thermal methanol reformer, and the V3 and V4 with compressed hydrogen tanks. The FCX‐V3 was introduced to the California Fuel Cell Partnership in Sacramento in November 2000. Operation of the vehicle over a wide variety of city roads and freeways has demonstrated that a fuel cell vehicle is roadworthy and performs capably in traffic. However, there remain areas for further improvements in order to bring fuel cell vehicles into the market.
Market concepts, competing technologies and cost challenges for automotive and stationary applications
Authors: Lipman T. , Sperling D.
Published: December 2010

Fuel cells have unique attributes that are attractive to automotive and electricity consumers, and also to automotive and electricity companies. These attributes include quiet and responsive operation, high efficiency, low fuel cycle emissions of criteria pollutants and greenhouse gases, and diversity of fuel supply. These features are highly valued in certain market niches and segments, and there are no obvious barriers to fuel cells' entry into the marketplace. Furthermore, three trends serve to reinforce the attractiveness of fuel cells: motor vehicles transitioning from mechanical and hydraulic systems to electrification, electricity generating moving toward distributed generation, and continuing international commitments to reduce greenhouse gas emissions and the environmental footprint of industrial products. However, despite great improvements in fuel cell power density over the past decade, and demonstration of promising performance, both stationary and automotive fuel cell systems face critical remaining challenges. These include primarily cost reduction, achievement of fuel cell system durability targets, development of efficient and low cost fuel reformers, and development of hydrogen storage systems for vehicles that are inexpensive, lightweight, compact, safe, and quick to refuel.
Platinum monolayer oxygen reduction electrocatalysts
Authors: Adzic R. R. , Lima F. H. B.
Published: December 2010

In this chapter, we review briefly the development of a class of highly promising platinum monolayer electrocatalysts that are characterized by a high activity for the oxygen reduction reaction, almost complete platinum utilization, and good long term performance stability. The properties of these electrocatalysts address the major problems of fuel cell electrocatalysis ‐ namely, the insufficient activity of platinum and its excess loading in fuel‐cell electrodes. A detailed analysis of platinum monolayer electrocatalysts is presented including the correlation of their activity with the center of the Pt d‐band, the effects of the types of supports namely, metal, alloy, core‐shell and oxide nanoparticles, and the corresponding mechanistic underpinnings afforded by electronic‐structure theory. In addition, a method of preventing Pt dissolution under certain potential regimes and the behavior of Pd monolayer electrocatalysts are described. Finally, we conclude with an assessment of long‐term fuel cell tests of selected electrocatalysts and their prospects for the future.
Transition metal/polymer catalysts forO2reduction
Authors: Johnston C. M. , Piela P. , Zelenay P.
Published: December 2010

Transition metal/polymer catalysts for O2reduction have been investigated extensively as a less expensive, more abundant alternative to platinum catalysts for polymer electrolyte fuel cell (PEFC) cathodes. Embedding metals into polymers offers many potential advantages analogous to the function of metal‐containing enzymes, which include bringing the metal centers into proximity for cooperative action and moderating the local pH near the metal to improve catalyst stability. In this article, we critically summarize the developments in this category of catalysts. While many of the anticipated benefits of the transition metal/polymer catalysts are still to be demonstrated, the most successful aspect of using polymer matrices thus far has been the improved durability. Some newer systems have shown stability for hundreds of hours in the real (acidic) PEFC environment, which was not previously observed for nonprecious catalysts of any type. Although the activity must be increased before any nonprecious metal catalysts are commercially viable, the rich chemistry of polymers allows for many pathways of improvement. We discuss current efforts to understand the structure and action of the active sites and, based on that discussion and research reported to date, suggest future work in the field of oxygen reduction electrocatalysis using transition metal/polymer catalysts.
First‐principles modeling for the electro‐oxidation of small molecules
Authors: Neurock M.
Published: December 2010

The electrocatalytic oxidation of small organic molecules is of great interest in the development of direct liquid fuel cells. While much is known concerning the overall electrocatalytic chemistry, the mechanisms and active sites which control these reactions remain elusive. The advances that have taken place in computation together with new method developments have made theory an invaluable partner with experiment in elucidating the mechanisms and sites that control electrocatalysis. Recent advances in ab initio methods for modeling electrochemical systems and their application to modeling the oxidation of methanol, formic acid and ethanol are discussed herein. The results reveal that while each of these fuels can be oxidized via direct and indirect routes, the controlling paths are function of the molecule as well as the size and configuration of the active surface sites. Methanol proceeds via indirect oxidation paths which require ensemble sizes of at least 3 metal atoms. Formic acid which internally contains CO
2
proceeds instead via a direct path over just 1–2 metal atoms. Ethanol is oxidized primarily to acetaldehyde and acetic acid and requires the presence of defect sites to activate the CC bond. The unique nature of the active site for each of these fuels reveals different alloying effects.
On the pathways of methanol and ethanol oxidation
Authors: Vielstich W. , Paganin V. A. , Alves O. B. , Ciapina E. G.
Published: December 2010

The knowledge on the different oxidation pathways of liquid fuels like methanol and ethanol at Pt‐based electrodes has improved recently. Parallel pathways are responsible for the kind of intermediates, the effective cell voltage, and for the amount of charge per fuel molecule. Both methanol and ethanol have a high thermodynamic energy density, 6000 and 8000 Wh kg
−1
, respectively. In alkaline media, better potential and current density data can be obtained. But the technical application is handicapped by carbonate formation and by a loss of OH
−
electrolyte. Therefore, reactions in acid media are studied and used in fuel cell systems.

This chapter reviews detailed investigations of the pathways of methanol oxidation at different Pt‐metal electrodes. Under optimized operating conditions, an optimum reaction sequence is obtained giving almost 6 e
−
per molecule.

In contrast to CH
3
OH, the two C atoms C
2
H
5
OH shows, at temperatures up to 80 °C, and on PtRu, PtSn, or PtPd as catalysts, less than 4 e
−
per molecule, i.e., at best acetic acid is formed. The main problem in the electrocatalysis of ethanol oxidation is the scission of the C‐C bond, necessary for yielding CO
2
. The detection of intermediates and products and the form of possible parallel pathways are demonstrated. Temperatures around 100 °C and above are problematic for simple fuel cell systems. But under these conditions and using Raney‐Pt catalysts, Sandstede demonstrated in the 1960s that an anodic oxidation of acetic acid is possible.
Effects of contaminants on catalyst activity
Authors: Garzon F. H. , Uribe F. A.
Published: December 2010

Hydrogen fuel and ambient air contaminants that exhibit strong electrode catalyst chemisorption may severely degrade the performance of polymer membrane fuel cells. Common fuel‐reforming impurities include carbon monoxide and hydrogen sulfide and air impurities include sulfur oxides and nitrogen oxides. CO contamination at parts per million (ppm) levels severely affects fuel cell performance; however, a number of methods including depolarization, air bleeding, and CO tolerant catalyst alloys will mitigate the performance losses. In contrast, the deposition of S on Pt surface from adsorption of sub‐ppm levels of H2S in the H2‐fuel stream results in severe fuel cell performance degradation. The oxidative removal of adsorbed S is a kinetically hindered process and is not achievable at reasonable rates in normal fuel cell operation.
Design rules for the improvement of the performance of hydrocarbon‐based membranes for proton exchange membrane fuel cells (PEMFC)
Authors: Gross M. , Maier G. , Fuller T. , MacKinnon S. , Gittleman C.
Published: December 2010

Many different polyelectrolytes have been synthesized over the past decades for application as proton‐conducting membranes in fuel cells. While many of them (polymers as well as membranes) are well studied, it is often hard to identify the specific benefits and drawbacks of one chemical structure over another. On the basis of observations of the effects of certain chemical structures as well as the architecture of the polymer chains on membrane properties such as proton conductivity, water uptake, and durability, this article tries to point out guidelines for the improvement of polyelectrolytes for fuel cell membranes. These guidelines concern polymer properties such as block structures, microphase‐separated morphologies, the type of the attachment of the acidic groups to the polymer chain, the effect of hydrophobicity, and others. The effects of these polymer properties on the behavior of the membrane are described and attempts at explanations for these observations are made.
High‐temperature polybenzimidazol‐based membranes
Authors: Seel D. C. , Benicewicz B. C. , Xiao L. , Schmidt T. J.
Published: December 2010

High‐temperature polybenzimidazole‐based membranes Polybenzimidazole (PBI) is an excellent material for phosphoric acid‐doped proton exchange membranes. PBI‐based membranes can operate reliably at temperatures above 120 °C, which provides high CO tolerance, fast electrode kinetics, and simplified water and thermal management. PBI membranes prepared by the polyphosphoric acid (PPA) process exhibit improved mechanical properties, proton conductivities, and fuel cell operational characteristics at higher phosphoric acid loading levels compared to the conventionally prepared PBI‐based membranes for high‐temperature fuel cell applications.
Highly durablePFSAmembranes
Authors: Endoh E.
Published: December 2010

Perfluorosulfonic 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

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

This 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

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.