bluuebunny/crossref_metadata_2025 huggingface dataset:
Life‐cycle analysis of fuel cell system components
Authors: Pehnt M.
Published: December 2010

Due to the efficient and (almost) zero emission operation of fuel cells, they are particularly attractive for application in the transportation sector and in stationary power conversion. For an environmental evaluation of new technologies, however, an investigation of the complete life‐cycle is necessary to ensure that no environmental aspect is neglected. In this “cradle‐to‐grave approach”, not only the use phase, but also the supply of the fuel and the production and disposal/recycling of the vehicle or power plant have to be considered. The appropriate instrument for this task is life‐cycle assessment (LCA).

This chapter presents LCAs of fuel cells in mobile and stationary applications with different fuel options and compares them to conventional power train or plant options focusing on different environmental aspects, such as use of resources, global warming, acidification and emission of carcinogenic substances. For this purpose, future developments of the fuel cell competitors, e.g., internal combustion engines, gas turbines, combined cycle plants, etc., have to be taken into account as well.

In vehicle applications, special focus is paid to the question of the best fuel, which is of considerable importance for the performance of fuel cell vehicles. The production of the required materials, e.g., catalyst materials and system components are also described and assessed.

In stationary systems, cogeneration applications using low and high‐temperature fuel cells are investigated thoroughly.
Influence of size on the electrocatalytic activities of supported metal nanoparticles in fuel cells related reactions
Authors: Maillard F. , Pronkin S. , Savinova E. R.
Published: December 2010

Recent publications related to the investigation of the size dependence of the catalytic activities of supported metal nanoparticles in fuel cell‐related processes, namely hydrogen oxidation, oxygen‐reduction, CO, formic acid, formaldehyde, and methanol oxidation reaction, are reviewed. The experimental data as well as theoretical modeling are presented for the influence of the particle size on the structural, electronic, adsorption, and catalytic properties. Analyses of the available literature proves unambiguously that a decrease in the particle size below ca 5 nm strongly affects specific electrocatalytic activities in fuel cell‐related processes, and this is of importance for the design of efficient catalysts for PEMFCs and DMFCs. Various approaches to explain the origin of the particle‐size effects in electrocatalysis are analyzed, with the conclusion that the observed variations in the electrocatalytic activities are induced by the intrinsic particle‐size effects, and are related to the changes in their structural and/or electronic properties, rather than by diffusion‐related phenomena.
Dealloyed
Pt
bimetallic electrocatalysts for oxygen reduction
Authors: Strasser P.
Published: December 2010

In this article we report on the concept, synthesis, structural characterization, and surface catalytic performance of a new class of multimetallic Pt alloy nanoparticle electrocatalysts for the electroreduction of molecular oxygen in polymer electrolyte membrane (PEM) fuel cell–relevant acidic environments. Rotating disk electrode measurements as well as single fuel cell tests have shown that this class of cathode catalysts yield Pt mass‐based and Pt surface‐area‐based oxygen reduction reaction (ORR) activities, which are a factor of 4–6 times higher than those of pure Pt. Hence, at present, this catalyst system constitutes one of the most active ORR catalyst systems ever reported.

We also present and discuss a novel method to deploy carbon‐supported dealloyed Pt bi‐ and multimetallic nanoparticles as cathode electrocatalysts in electrode layers of single fuel cell membrane electrode assemblies (MEAs). We demonstrate the voltammetric insitu preparation of dealloyed bimetallic Pt–Cu, and report preliminary results on dealloyed Pt–Co–Cu ternary cathode electrode catalysts. We conclude with a discussion of our current hypothesis as to the mechanistic origin of the catalytic activity enhancement as well as with preliminary results as to the stability of this class of catalysts.
Time to move beyond transition metal —
N
—
C
catalysts for oxygen reduction
Authors: Garsuch A. , Bonakdarpour A. , Liu G. , Yang R. , Dahn J. R.
Published: December 2010

FeNC and CoNC electrocatalysts have been studied for many years by numerous research groups. Various synthesis routes, involving different precursors, different temperatures, etc., have been employed, but “successful” catalysts share the common features of Fe or Co, N, and C and a heat‐treatment step to around 800 °C. It is our contention that the thermodynamics, not the details of the precursors or synthesis steps, determines the local atomic arrangement of Fe, N, and C or Co, N, and C in these catalysts after heating and, as such, the catalysts prepared by all researchers in this field are basically the same. In this article, compelling evidence for this contention is presented. These catalysts, presumably all, share the same advantages, which include reasonable activity, and disadvantages, which include short lifetime. Therefore, the study of FeNC and CoNC catalysts is overpopulated by researchers, and most should probably shift their focus to the search for new nonnoble metal catalysts involving other elements in the periodic table.
Reaction pathway analysis and reaction intermediate detection via simultaneous differential electrochemical mass spectrometry (
DEMS
) and attenuated total reflection fourier transform infrared spectroscopy (
ATR
‐
FTIRS
)
Authors: Heinen M. , Jusys Z. , Behm R. J.
Published: December 2010

A newly developed hyphenated technique, the combination of
in situ
attenuated total reflection Fourier transform infrared spectroscopy (ATR‐FTIRS), on‐line differential electrochemical mass spectrometry (DEMS), and electrochemical flow‐cell measurements, is described and its potential for studies of electrocatalytic reactions relevant for fuel cell operation is outlined. This method allows the simultaneous detection of adsorbed reaction intermediates (
in situ
ATR‐FTIRS), volatile reaction products (on‐line DEMS), and the total Faradaic current (electrochemical measurements) at the same time, in a single experiment, under enforced and controlled electrolyte transport conditions. It also allows us to follow the adsorption process in electrolyte‐exchange transients at constant potential, which is important for kinetic studies.

The potential of this method is illustrated in different examples. CO uptake transients from the CO‐containing electrolyte show the influence of the potential on the CO adsorption kinetics. Using isotope‐labeled CO, similar information can be obtained on CO
ad
exchange, demonstrating rapid exchange for CO adsorbed on Pt even at room temperature. Adsorption/oxidation transients and potentiodynamic measurements of the oxidation of C
1
and C
2
molecules are presented and discussed, which illustrate the potential of this method for determining the dynamics, kinetics, and mechanism of the adsorption and oxidation of small organic molecules, by combining parallel information on the contributions of different reaction pathways (product analysis) and adsorbed reaction intermediates at different stages of the adsorption/reaction process and under different reaction conditions. Finally, future developments and prospects of this method are outlined.
Methanol oxidation on oxidized
Pt
surface
Authors: Varela H. , Sitta E. , Batista B. C.
Published: December 2010

The direct methanol fuel cells (DMFCs) have been recognized as a very interesting alternative for portable and stationary applications mainly owing to their potential use as an environment friendly technology, Besides the sluggish kinetic of alcohol oxidation at the anode and oxygen reduction at the cathode, an important problem associated with the use of DMFCs is the fuel transport from the anode to the cathodic compartment. The parallel reactions of alcohol oxidation and oxygen reduction result in the formation of a mixed potential at the cathode, which considerably decreases the overall cell performance. We present in this chapter some experimental aspects of the interaction of methanol with oxidized platinum surfaces under open‐circuit conditions. First, the effect of alcohol crossover from the anodic to the cathodic compartment through the electrolytic membrane is presented. Then the method of recording transients of the open circuit potential as a way of studying the interaction of organic molecules with oxidized platinum surfaces is shown and some key results are reviewed. Afterward some mechanistic aspects are discussed and reaction pathways suggested.
Mechanistic aspects of carbon monoxide oxidation
Authors: Iwasita T. , Ciapina E. G.
Published: December 2010

Some experimental and theoretical approaches to formulating a reaction mechanism for carbon monoxide (CO) oxidation at Pt‐based catalysts are discussed. According to these, it is likely that the reaction takes place at steps and defect sites on the surface, thus called
active sites
. On these sites, dissociation of water occurs and CO from the terraces diffuses to the active sites, where a Langmuir–Hinshelwood mechanism between CO
ad
and OH
ad
takes place. Potentiostatic and potentiodynamic data for CO stripping at nanoparticles show that the oxidation occurs with a higher rate at large nanoparticles following the same reaction mechanism as for extended surfaces with a high rate of CO diffusion. In contrast, at small particles (∼1 nm) CO diffusion is rate determining. It is shown that an L–H mechanism is also operative in the presence of dissolved CO, in spite of the high degree of CO surface coverage. Under the latter conditions, large currents are observed in the prepeak region if CO is preadsorbed at potentials below the potential of zero charge (pzc) (∼0.30 vs standard hydrogen electrode — SHE). CO preadsorption above this potential causes an inhibition of CO oxidation. This inhibition is likely due to the formation of icelike water clusters, mainly at the steps. This interpretation is based on Fourier transform infrared spectroscopy (FTIRS) and scanning tunneling microscopy (STM) data. Adsorbed anions have an inhibiting effect on both monolayer and bulk CO oxidation. The enhancement of CO oxidation by PtRu and PtSn is discussed in the light of recently developed theories on bimetallic catalysts.
Catalyst and catalyst‐support durability
Authors: Wagner F. T. , Yan S. G. , Yu P. T.
Published: December 2010

Automotive duty cycles impose multiple mechanisms for the loss of kinetic activity of oxygen‐reduction catalysts for proton‐exchange membrane fuel cells. Load cycling causes dissolution of Pt into the electrolyte, leading to the growth of larger Pt particles with lower specific surface area and to the permanent loss of Pt into the ionomer phase, where it is no longer active. An increase in the activity per surface Pt atom during cycling partially compensates for the former, but not the latter, loss mechanism. Higher initial activities can be achieved with Pt‐alloy catalysts, but these may bring additional loss mechanisms into play. Corrosion of the carbon support can decrease both the kinetic activity of the catalyst and the ability of the fuel cell to sustain high current densities. The rates of carbon corrosion depend strongly on both the type of carbon used and the fuel cell operating conditions, but all types of carbon seem to exhibit significant fuel cell performance loss after ∼10% of the carbon is consumed. Noncarbon supports give promise of improved durability under severe conditions, but their practical use will require improved control over bulk physical properties, surface chemistry, and pore structure.
Radiation‐grafted proton conducting membranes
Authors: Gubler L. , Scherer G. G.
Published: December 2010

Proton exchange membranes have to fulfil two main functionalities in the membrane electrode assembly (MEA) of a polymer electrolyte fuel cell (PEFC): (i) transport protons from the anode to cathode and (ii) separate anode and cathode electrodes and reactants. Radiation grafting offers a versatile method to introduce proton conductivity into a preformed base polymer film. Base polymers and graft monomers can be selected from a wide range of commercially available commodity products. In this article, synthetic routes and parameters to control membrane composition and morphology are discussed. The choice of a base film and monomers, in particular crosslinkers, has large influence on the resulting membrane properties and fuel cell performance. To fulfil and sustain the separator functionality, dimensional stability and mechanical properties are of high importance. The development of materials for fuel cells and the need to further the understanding of limiting processes and degradation phenomena require a well‐assorted toolbox forex situandin situcharacterization of properties and performance. Implementation of accelerated test methods andpost mortemanalysis on a local scale have helped in enhancing the throughput of samples and gain further insight into prevailing degradation mechanisms.
Colloidal structure of ionomer solutions
Authors: Gebel G.
Published: December 2010

The discovery of an efficient process to “dissolve” Nafion at the beginning of the 1980s has boosted the development of efficient fuel cells. Indeed, the preparation of electrodes with very high active areas, of homogeneous and thin membranes by solution casting, and of new composite membranes then became possible. After a short review on swelling properties and dissolution of Nafion membranes, this article focuses on the structure and properties of these solutions and on the obtaining of membranes by solution casting. The small‐angle X‐ray and neutron scattering studies combined with light scattering and magnetic resonance data point out the colloidal structure of these solutions. The question of the existence of isolated polymer chains is still under debate. However, the analysis of the dilute solution scattering patterns revealed the presence of large elongated particles with a size directly related to the volume of the fluorinated polymer associated to each ionic group. This structure was confirmed by electron and atomic force microscopy pictures. The particle diameter was shown to be strongly related to polymer solvent interactions. This parameter also has a great influence on the properties of the solution‐cast films and consequently it has a great impact on the electrode microstructure in membrane electrode assemblies (MEA). The light scattering studies revealed a limited stability with a strong predisposition to aggregate in larger particles. A post‐thermal treatment is often necessary to restore properties similar to those of the pristine Nafion membrane.
Chemical and mechanical membrane degradation
Authors: Liu W. K. , Cleghorn S. J. C. , Delaney B. E. , Crum M.
Published: December 2010

In order to advance the fundamental understanding of the mechanism of polymer electrolyte membrane degradation and facilitate the development of new technologies, it is imperative to establish reliable, critical tests. It is now widely recognized that membrane degradation and failure proceeds by two interacting mechanisms: ionomer chemical degradation and membrane mechanical failure. This article focuses on the test methods developed that both separate and accelerate these two individual mechanisms, as well as the mechanistic learnings that have been discovered.In situuniform fuel cell and tradition fuel cell experiments have been used to explore operational effects such as current density, relative humidity, membrane iron content, and cyclic operation on the rate of ionomer chemical degradation. In addition, newex situvapor‐phase Fenton's reagent experiments have been used to further determine why fuel cell ionomer degradation rates do not always correlate with the results of traditional Fenton's reagent tests. In addition, in‐cell relative humidity cycling tests are conducted in an inert environment to isolate the mechanical failure mode of fuel cell membranes, and then fuel cell reactants are introduced to combine mechanical and chemical degradation mechanisms. At this point, the relative rates of the two mechanisms are explored. Finally, results of long‐term fuel cell tests are reported at more realistic conditions for today's automotive applications.
Mechanical durability characterization and modeling of ionomeric membranes
Authors: Lai Y. H. , Dillard D. A.
Published: December 2010

Many of the premature failures in proton exchange membrane (PEM) fuel cells are attributed to the crossover of reactant gases through cracks developing in the membrane during fuel cell operation. Postmortem analysis of membranes subjected to fuel cell humidity cycling tests in the absence of electrochemical reaction suggests that membrane cracks are driven by the in‐plane tensile stress state that develop within the membrane during cyclic hygrothermal loading. This article presents an effort to develop a suite of analytical and experimental methods within a framework of viscoelasticity to characterize the mechanical stresses, constitutive properties, strength, and durability/lifetime of proton exchange membranes. The success obtained in accounting for a range of observed phenomena suggests the applicability and usefulness of this framework.
Mechanistic understanding and electrochemical modeling of mixed conducting (SOFC) electrodes
Authors: Merkle R. , Maier J. , Fleig J.
Published: December 2010

In this article it is shown how the phenomenological transport parameters measured on a mixed conducting solid oxide fuel cell (SOFC) cathode are related to the underlying fundamental quantities, such as bulk defect concentrations and mobilites, and surface reaction mechanism and corresponding equilibrium exchange rate. Complications due to charged oxygen adsorbates and arising under an applied dc bias are discussed. Dense thin‐film microelectrodes are shown to serve as valuable model systems for achieving a mechanistic understanding and obtaining reliable experimental data.
New high‐temperature proton conductors for fuel cells and gas separation membranes
Authors: Haugsrud R.
Published: December 2010

High‐temperature proton conductors and mixed proton–electron conductors have the potential to serve as membranes in processes within future environment‐friendly energy technologies. Proton‐conducting solid oxide fuel cells (PC‐SOFCs) offer, among other advantages, better and simpler fuel utilization than conventional SOFCs. Mixed proton–electron conductors may be applied as membranes for hydrogen production and purification with the advantage of 100% selectivity, higher operation temperature, and improved long‐term stability compared to present membrane candidate materials. State‐of‐the‐art high‐temperature proton‐ and mixed proton–electron conductors consist of the basic alkaline‐earth cerates and zirconates. The reactivity of these materials with, in particular CO2, has so far limited implementation of high‐temperature proton conductors in industrial processes. Consequently, there is a need for new materials that combine the required functional properties with sufficient mechanical and chemical stability. The present contribution summarizes the literature on high‐temperature proton conductors with emphasis on newly developed materials. The functional characteristics of the materials are discussed in view of the current understanding of thermodynamics, transport parameters, and physical material properties.
Nanoimpact on electrode and electrolyte layers with micro‐electro‐mechanical system (
MEMS
) technique
Authors: Premchand Y. D. , Bieberle‐Hütter A. , Galinski H. , Rupp J. L. M. , Ryll T. M. , Scherrer B. , Tölke R. , Yang Z. , Harvey A. , Evans A. , Xu L. , Gauckler L. J.
Published: December 2010

MEMS (micro‐electromechanical system) fabrication of solid oxide fuel cells to realize portable power sources, does not only mean a reduction of the spatial geometry of all components of a fuel cell but also means that with decreasing electrolyte and electrode layer thicknesses as well as grain size of these components, the nanoeffects become important. It therefore offers new challenges for understanding the influence of electrode and electrolyte layer properties for material integration as well as modeling. The nanoscale impact on electrolyte and electrode layers as well as micro‐SOFC cell characteristics are described in this article.
Durability of metallic interconnects and protective coatings
Authors: Yang Z. G. , Stevenson J. W.
Published: December 2010

To build up a useful voltage, a number of solid oxide fuel cells (SOFCs) are electrically connected in series in a stack via interconnects that are placed between adjacent cells. In addition to functioning as a bipolar electrical connector, the interconnect also acts as a separator plate that separates the fuel at the anode side of one cell from the air at the cathode side of an adjacent cell. During SOFC operation at high temperatures, the interconnects are thus simultaneously exposed to the oxidizing air at one side and a reducing fuel, which can be either hydrogen or hydrocarbon, at the other. Besides, they are in contact with adjacent components, such as electrodes or electrical contacts, seals, etc. With steady reduction in SOFC operating temperatures into the low or intermediate range of 600–850 °C, oxidation‐resistant alloys are often used to construct interconnects. However, the metallic interconnects may degrade via interactions at their interfaces with surrounding environments or adjacent components, potentially affecting the stability and performance of interconnects and the SOFC stacks. Therefore protection layers are applied to metallic interconnects, which are also intended to mitigate or prevent chromium migration into cells and the cell poisoning. This article provides a comprehensive review of materials for metallic interconnects, their degradation, and coating protection.
Impact of impurities and interface reaction on electrochemical activity
Authors: Mogensen M. , Hansen K. V.
Published: December 2010

The surfaces and interfaces of usual electrolytes for solid oxide fuel cells (SOFCs) such as stabilized zirconia and doped ceria tend to be covered strongly by glassy phases consisting of SiO2, Na2O, and other glass‐forming oxides. Even in case of very clean single crystals a “monolayer” of impurities of similar “glassy” composition is usually observed on the surface of yttria‐stabilized zirconia (YSZ). Furthermore, dopants like Y2O3in YSZ and Gd2O3in ceria gadolinia oxide (CGO) segregate to the grain boundaries as well as to the interface between the bulk crystal and the glassy surface layer. Perovskite electrode materials, ABO3, where A is a big and B is a small metal ion, exhibit surface layers enriched in A‐oxides. Generally, the electrode polarization resistance increases with increasing amount of surface segregations. Deleterious reactions between the segregated impurities and the cell components may take place at the interfaces, and the viscous glassy phases may act as diffusion paths that allow solid‐state reactions, which otherwise would be kinetically hindered. The driving forces for both impurity and dopant segregations are, in general, the changes in interface free energy between clean and covered interfaces.
Application of secondary ion mass spectrometry (
SIMS
) technique on the durability of solid oxide fuel cell (
SOFC
) materials
Authors: Yamaji K. , Sakai N. , Kishimoto H. , Horita T. , Brito M. E. , Yokokawa H.
Published: December 2010

In this article, we introduce secondary ion mass spectrometry (SIMS) technique as a powerful tool to analyze the trace of mass transport at the interface of solid oxide fuel cell (SOFC) components. SOFC consists of several complex oxides and metals that are considered to be more stable than other types of fuel cells. However in a long term operation, the mass transport that occurs on the surface and interfaces of SOFC components will severely affect the degradation of cell performance, even though the flux of mass transport was very small. SIMS has many disadvantages as an analysis apparatus; its advantages are very unique. By combining the conventional scanning electron microscopy and energy dispersive X‐ray spectrometer (SEM/EDX) analyses, one can get more precise and new results for small concentration changes in the vicinity of surface and interfaces. The application of such combined analysis technique will be very important to investigate the degradation mechanism of SOFCs. In the following chapter, we show some examples of the SIMS application.
Durability of cathodes includingCrpoisoning
Authors: Menzler N. H. , Mai A. , Stöver D.
Published: December 2010

This article deals with the durability of solid oxide fuel cell (SOFC) cathodes, especially perovskites of the lanthanum–strontium–manganite (LSM) and lanthanum–strontium–cobalt–ferrite (LSCF) types. Both cathode materials were characterized with respect to either the intrinsic degradation behavior depending on, for example, time, temperature, current density, chemical composition, or the influence of the gaseous chromium species that originate from the oxide layer on the metallic interconnects. Results are presented for single‐cell tests and stack tests. Additionally, in the sections describing the influence of Cr on cathode degradation, some basic results are presented on the interaction of single oxides or oxide mixtures with chromium‐containing atmospheres.
Durable sealing concepts with glass sealants or compression seals
Authors: Buchkremer H. P. , Conradt R.
Published: December 2010

Solid oxide fuel cell (SOFC) systems allow efficient direct conversion from chemical to electrical energy. But the commercialization of the technology is strongly dependent on the development of cost‐effective, long‐term stable materials and seals. Sealing components in SOFC stacks have to fulfill a large variety of requirements. Primarily, they should separate the oxidants and fuel gases under all operating conditions, e.g. thermal cycling, rapid heating/cooling, temperature gradients. In this article, the state‐of‐the‐art knowledge in SOFC sealing technology is described for the two main development directions—glass sealants and compressive sealants
Design approaches for determining local current and membrane resistance in polymer electrolyte fuel cells (PEFCs)
Authors: Freunberger S. A. , Reum M. , Büchi F. N.
Published: December 2010

In polymer electrolyte fuel cells, several relevant scales determine the local current distribution. For the scales of flow field structures, the full cell and in‐between‐cells in a stack, different methods have been developed for the local current measurement. The respective measurement principles on the three scales are introduced and discussed. On the full cell scale, a number of methods based on some sort of segmented cell have been developed and have become a standard diagnostic tool, whereas on the channel/rib scale only one method, which uses the current drain asin situshunt resistor has been put forward.

The methods for measuring local current density on the different scales form a basis for all methods determining the local membrane resistance.
Proton exchange membrane fuel cell (PEMFC) flow‐field design for improved water management
Authors: Allen J. S. , Son S. Y. , Collicott S. H.
Published: December 2010

Channel blockage in the form of liquid water or ice can result in severe degradation of fuel cell components. Thus, the durability of PEM fuel cells is dependent upon effective water management. Many mechanisms affect water management. The mechanism responsible for liquid plug formation is capillarity. Water does not appear in the channels in the form of a plug, rather water enters the channel as a drop through the diffusion media. Capillarity is responsible for the transition from a drop or a film of water into a plug which occludes the channel. The purpose of this chapter is to review the destabilization mechanisms responsible for plug formation in the flow channels. We also discuss analytical and computational tools that may be used to predict the behavior of the liquid water in the flow‐field channels. These tools may also be used to design channel features that can improve water management in the flow field.
Performance impact of cationic contaminants
Authors: Pivovar B. S. , Kienitz B. , Rockward T. , Uribe F. A. , Garzon F. H.
Published: December 2010

Although a major amount of research has been undertaken on failure modes of fuel cell durability, relatively little research has been carried out on cationic contamination. One of the primary issues of cationic contamination is the low level of contaminant needed to impact a cell. The uptake of contaminant cations leads to dramatically decreased performance even at low levels of incorporation. Foreign cations replacing protons in the ionomer phase likely increase ohmic, kinetic, and mass transport losses in the cell and may alter cell thermodynamics. At this point in time, little is known about the rates of exposure, uptake, and escape of contaminant cations in operating fuel cells. The extent of performance loss following cationic contamination and recovery of performance after contamination are discussed in terms of cation contaminant impact on fuel cell durability.
Performance modeling and cell design for high concentration methanol fuel cells
Authors: Shaffer C. E. , Wang C. Y.
Published: December 2010

For direct methanol fuel cells (DMFCs) to compete with and replace lithium‐ion batteries as power sources for mobile devices, they must be designed to increase their energy density. One major hurdle in accomplishing this task is being able to use high concentration methanol fuel, thereby reducing the size of the fuel tank and the amount of water carried as part of the system (water is a reactant in methanol oxidation). Much effort has been made to reduce the methanol crossover from anode to cathode, but there has been relatively less awareness of water transport and its importance in enabling the use of high concentration methanol fuel. In this article, we review the scientific principles and state‐of‐the‐art technology for high concentration methanol fuel cells (HC‐MFCs). We demonstrate a direct link between water crossover through the membrane and the allowable methanol concentration in the fuel through intuitive examples and pertinent case studies, and further review current means by which water loss to the cathode side of a DMFC is reduced. Future HC‐MFC designs are expected to include the continued progress in membrane electrode assemblies (MEAs) that use unique porous layer properties to simultaneously reduce methanol crossover and enhance water backflow from cathode to anode, as well as development of membrane materials with increased resistance to methanol transport and simultaneous increased diffusivity of water.
New diagnostic methods for polarized state
Authors: Kawada T.
Published: December 2010

Electrode polarization is a key to determine the dynamic feature of solid oxide fuel cells (SOFCs). Recently, various methods have been proposed for the evaluation of the electrode under the polarized state. Photoelectron spectroscopy and infrared spectroscopy have been applied to detect the surface intermediate species. Raman spectroscopy is a useful tool for high‐temperaturein situmeasurements, and is used for the study of carbon deposition and sulfur poisoning, etc. Attempts were made to measure the local oxygen potential in the electrode layer in order to evaluate the oxygen reaction pathway. The potentiometric method and X‐ray absorption were employed for thein situmeasurement. Isotope exchange and secondary ion mass spectrometry analysis were also used to trace the oxygen reaction path. Although most of the new techniques are still under development, the information obtained from these measurements gives new insight on electrode reaction kinetics.
Carbon‐support corrosion mechanisms and models
Authors: Gallagher K. G. , Darling R. M. , Fuller T. F.
Published: December 2010

The most significant challenges to the commercialization of fuel cells are cost and durability. The electrochemical oxidation of carbon in low‐temperature fuel cells reduces the lifetime of these power plants. This article presents a current understanding of carbon oxidation and corrosion mechanisms that accelerate the reaction. Carbon is oxidized under various conditions including the reverse‐current mechanism, which occurs when a fuel cell is started or stopped and during localized fuel starvation. Models and mitigation strategies are presented to enhance the understanding of the reverse‐current mechanism. We conclude that a combined system and material mitigation strategy is necessary to overcome this corrosion mechanism.
Field experience with fuel cell vehicles
Authors: Wipke K. , Sprik S. , Kurtz J. , Garbak J.
Published: December 2010

The “Controlled Hydrogen Fleet and Infrastructure Demonstration and Validation Project”, also known asthe Fuel Cell Vehicle and Infrastructure Learning Demonstration, is a 5‐year US Department of Energy (DOE) project started in 2004. The purpose of this project is to conduct an integrated field validation that simultaneously examines the performance of fuel cell vehicles and the supporting hydrogen infrastructure. NREL has now analyzed data from almost 3 years of the 5‐year project. During this time, 92 vehicles have been deployed, 15 project refueling stations have been placed in use, and no fundamental safety issues have been identified. We have analyzed data from over 200 000 individual vehicle trips covering 1, 770, 278 km traveled and over 40 000 kg hydrogen produced or dispensed.

Public analytical results for this project are in the form of composite data products, which aggregate individual performance into a range that protects the intellectual property and the identity of each company, while still publishing overall status and progress. One of the key metrics from the project is fuel cell durability. We analyze all of the field data from the fuel cell vehicles, and make degradation projections based on a theoretical 10% drop in voltage at high current. Recent projections show that a four‐team average projected time to a 10% drop in voltage is 1200 h. In the next 6 months, we will work to improve the accuracy of the voltage degradation projections by adding a fixed initial voltage and/or a nonlinear fit to avoid potentially overestimating the projected time that could occur as the accumulated hours continue to grow. To understand the cause of the gradual degradation of the stacks, we characterize how each stack is used and then perform multivariate analysis on this dataset to examine dominant variables affecting stack voltage degradation rate. High‐level public results have been extracted and detailed individual team results are also useful to the teams and for feeding back trends into the research and development program. Fuel cell system efficiency at one‐fourth power has been analyzed and compared with the DOE target of 60%; system efficiency results from the four teams ranged from 52.5 to 58.1%. A total of 47 composite data products have been published to date and made directly accessible to the public from our Hydrogen Technology Validation web site.
Sulfur poisoning onNicatalyst and anodes
Authors: Bøgild Hansen J. , Rostrup‐Nielsen J.
Published: December 2010

The impact of sulfur on the performance of nickel‐based fuel‐processing catalyst as well as anodes in SOFC plants is described. The thermodynamic basis as well as experimental findings are reviewed. The consequences for plant design and operation are also discussed.
Field experience with molten carbonate fuel cells (
MCFCs
) and solid oxide fuel cells (
SOFCs
) with an emphasis on degradation
Authors: Frey H. , Kessler A. , Münch W. , Edel M. , Nerlich V.
Published: December 2010

Fuel cells are a very important technology for a utility because they could affect our core business in the future. In the near future, if an increasing number of households produce their own electricity, then we might have to cope with a decline in sales. For this reason, Energie Baden‐Württemberg AG (EnBW) had embarked on the first fuel cell project at the end of the year 2001 to gain experience with the technical and economical maturity of this technology. Since then, more than 20 projects have followed; hence, we have good experience concerning the operation of fuel cell systems. For our business, it is important to assess the state of the art of the systems. Therefore, we are carrying out a great variety of demonstration projects.

In this report, we summarize the results of the operation of our fuel cell systems and our experience concerning degradation issues. The relevant systems are 16 solid oxide fuel cell (SOFC) HXS 1000 PREMIERE from Hexis, 1 Galileo 1000 N from Hexis, and 2 molten carbonate fuel cells (MCFCs) Hot Modules from CFC Solutions (formerly MTU). The SOFC systems are suited for home energy supply in different buildings. The two MCFC systems have an electrical output of a maximum of 250 kW and a thermal output of a maximum of 180 kW. One of these has been operated with natural gas and the other with biogas for the first time worldwide.
Local transient techniques in polymer electrolyte fuel cell (
PEFC
) diagnostics
Authors: Schneider I. A. , Scherer G. G.
Published: December 2010

The polymer electrolyte fuel cell (PEFC) is a complex macroscopic electrochemical reactor. Its performance is governed by the interplay of various processes, which occur on different length and timescales. Transient techniques provide a basis for understanding limiting processes, material properties, and degradation phenomena. A variety of transient techniques have entered the field of PEFC diagnostics: linear sweep and cyclic voltammetry (LSV, CV), potential and current step, and electrochemical impedance spectroscopy (EIS). Transient techniques have been used for the in situ characterization of a PEFC up to the complex stack level. Yet, by contrast, conclusions deduced from transient response are almost exclusively limited to phenomena within the most elemental part of a PEFC, the membrane electrode assembly (MEA). This perception, however, neglects the fact that in a technical PEFC processes in three spatial dimensions determine local cell performance and therefore, transient response. In contrast to integral measurements, local transient techniques account for the inhomogeneous operation of a PEFC. In this article, key results obtained by using local CV, EIS, and current step technique are discussed. Thereby, we focus on phenomena in local and overall transient response of a PEFC, which are linked to processes along the flow channels. It is shown that their identification and consideration is crucial for a meaningful interpretation of results
Properties of Flame Sprayed Ce0.8Gd0.2O1.9‐δ Electrolyte Thin Films
Authors: Karageorgakis Nikolaos I. , Heel Andre , Rupp Jennifer L. M. , Aguirre Myriam H. , Graule Thomas , Gauckler Ludwig J.
Published: December 2010

Thin films of Ce0.8Gd0.2O1.9‐δ (CGO) are deposited by flame spray deposition with a deposition rate of about 30 nm min−1. The films (deposited at 200 °C) are dense, smooth, and particle‐free and show a biphasic amorphous/nanocrystalline microstructure. Isothermal grain growth and microstrain are determined as a function of dwell time and temperature and correlated to the electrical conductivity. CGO films annealed for 10 h at 600 °C present the best electrical conductivity of 0.46 S m−1 measured at 550 °C. Reasons for the superior performance of films annealed at low temperature over higher‐temperature‐treated samples are discussed and include grain‐size evolution, microstrain relaxation, and chemical decomposition. Nanoindentation measurements are conducted on the CGO thin films as a function of annealing temperature to determine the hardness and elastic modulus of the films for potential application as free‐standing electrolyte membranes in low‐temperature micro‐SOFCs (solid oxide fuel cells).
Rylene and Related Diimides for Organic Electronics
Authors: Zhan Xiaowei , Facchetti Antonio , Barlow Stephen , Marks Tobin J. , Ratner Mark A. , Wasielewski Michael R. , Marder Seth R.
Published: December 2010

Organic electron‐transporting materials are essential for the fabrication of organic p‐n junctions, photovoltaic cells, n‐channel field‐effect transistors, and complementary logic circuits. Rylene diimides are a robust, versatile class of polycyclic aromatic electron‐transport materials with excellent thermal and oxidative stability, high electron affinities, and, in many cases, high electron mobilities; they are, therefore, promising candidates for a variety of organic electronics applications. In this review, recent developments in the area of high‐electron‐mobility diimides based on rylenes and related aromatic cores, particularly perylene‐ and naphthalene‐diimide‐based small molecules and polymers, for application in high‐performance organic field‐effect transistors and photovoltaic cells are summarized and analyzed.
Competition between hydrotreating and polymerization reactions during pyrolysis oil hydrodeoxygenation
Authors: De Miguel Mercader F. , Koehorst P. J. J. , Heeres H.J. , Kersten S. R. A. , Hogendoorn J. A.
Published: December 2010

Hydrodeoxygenation (HDO) of pyrolysis oil is an upgrading step that allows further coprocessing of the oil product in (laboratory‐scale) standard refinery units to produce advanced biofuels. During HDO, desired hydrotreating reactions are in competition with polymerization reactions that can lead to unwanted product properties. To suppress this polymerization, a low‐temperature HDO step, referred to as stabilization, is typically used. Small batch autoclaves have been used to study at near isothermal conditions the competition between hydrotreating and polymerization reactions. Although fast polymerization reactions take place above 200°C, hydrogen consumption was already observed for temperatures as low as 80°C. Hydrogen consumption increased with temperature and reaction time; however, when the end temperature exceeded 250°C, hydrogen consumption achieved a plateau. This was thought to be caused by the occurrence of fast polymerization reactions and the refractivity of the products to further hydrotreating reactions. The effect of the gas–liquid mass transfer was evaluated by using different stirring speeds. The results of these experiments (carried out at 300°C) showed that in the first 5 min of HDO, gas–liquid mass transfer appears to be limiting the overall rate of hydrotreating reactions, leading to undesired polymerization reactions and product deterioration. Afterward, intraparticle mass transfer/kinetics seems to be governing the hydrogen consumption rate. Estimations on the degree of utilization (effectiveness factor) for industrially sized catalysts show that this is expected to be much lower than 1, at least, in the early stage of HDO (first 30 min). Catalyst particle size should, thus, be carefully considered when designing industrial processes not only to minimize reactor volume but also to improve the ratio of hydrotreating to polymerization reactions. © 2011 American Institute of Chemical Engineers AIChE J, 2011
Undulating topography of HfO2 thin films deposited in a mesoscale reactor using hafnium (IV) tert butoxide
Authors: Li Kejing , Zhang Lin , Dixon David A. , Klein Tonya M.
Published: December 2010

HfO2 was deposited by chemical vapor deposition on Si, native SiO2, and borosilicate glass surfaces using hafnium (IV) tert butoxide in a mesoscale flow reactor. Undulating thin film topographies were observed by atomic force microscopy on all substrates with peak‐to‐peak periods between 10 and 25 nm in the presence of a temperature gradient perpendicular to flow of 25°C/mm. A computational fluid dynamic model suggests the phenomenon originates from buoyancy driven roll type flow. The thickness uniformity and roughness of the films depended on the flow rate, reactor temperature, and the substrate type. © 2011 American Institute of Chemical Engineers AIChE J, 2011
Nickel phosphide catalyst for autothermal reforming of surrogate gasoline fuel
Authors: Liu Lei , Hong Liang
Published: December 2010

An investigation into the catalytic autothermal reforming (ATR) of a mixture of n‐octane and naphthalene (6 wt %), designed as a surrogate gasoline, is undertaken. Carbon deposition on the metallic Ni catalyst has been aware of the main hurdle for the catalytic reforming of hydrocarbons especially those with high carbon numbers. This work develops NixPy crystallites on a CeO2 powder support by electroless nickel plating and calcination. The catalyst exhibits nil coking extent after reforming the surrogate fuel. The NixPy crystallites are determined by XRD and its Ni‐P bonding is confirmed by XPS, where the Ni carries slightly higher negative charge than the Ni0 as usually observed. The XPS investigation also divulges the presence of Ce3+ species in the CeO2 support on which the NixPy crystallites are distributed, indicating that the support contains oxygen vacancies. These two subtle structural differences are proposed to provide the catalyst with resistance to coking. © 2011 American Institute of Chemical Engineers AIChE J, 2011
Process‐based graphical approach for simultaneous targeting and design of water network
Authors: Deng Chun , Feng Xiao , Ng Denny Kok Sum , Foo Dominic Chwan Yee
Published: December 2010

A new process‐based graphical approach (PGA) is presented for the simultaneous targeting and design of water network. The PGA is extended from the limiting water profile which was developed for flow rate targeting for a water network. Via PGA procedure, apart from locating the minimum freshwater and wastewater flow rate targets, the water network that corresponds to the minimum flow rate targets is also synthesized simultaneously. The proposed approach handles both fixed load (including operations with water loss and/or gain) and fixed flow rate problems equally well. In addition, the approach can be used to synthesize direct reuse/recycle, regeneration reuse/recycling, and total water network. Furthermore, the proposed approach is applicable for water network with multiple freshwater sources. Three literature examples are presented to illustrate the proposed approach. © 2011 American Institute of Chemical Engineers AIChE J, 2011
Synthesis and characterization of novel graft copolymers by radiation‐induced grafting
Authors: Işıkel Şanlı Lale , Alkan Gürsel Selmiye
Published: December 2010

The radiation‐induced graft copolymerization of N‐vinyl‐2‐pyrrolidone (NVP), 4‐vinyl pyridine (4VP), and 2‐vinyl pyridine (2VP) monomers onto poly (ethylene‐alt‐tetrafluoroethylene) (ETFE) was investigated. The influence of synthesis conditions particularly the solvent was studied. Various solvents, such as n‐propanol, isoproponol, benzyl alcohol, methanol, ethanol, cyclohexanone, tetrahydrofuran (THF), nitromethane, 1,4‐dioxane, and n‐heptane were examined for this purpose. Graft copolymers were characterized by Fourier transform infrared (FTIR) spectroscopy, dynamic mechanical analysis (DMA), and scanning electron microscopy‐energy dispersive spectroscopy (SEM‐EDAX). It was found that the nature of the solvent had profound influence over the grafting reaction. Cyclohexanone, n‐propanol, and isoproponol for 4VP/ETFE grafting, THF and 1,4‐dioxane for NVP/ETFE grafting, and benzyl alcohol and methanol for 2VP/ETFE grafting were found to be the suitable solvents yielding highest graft levels. Isoproponol and n‐propanol are promising in terms of both graft level and mechanical properties for 4VP/ETFE. Grafting of NVP, 4VP, and 2VP onto ETFE were verified through FTIR spectroscopy. Storage modulus and glass transition temperature of the copolymers were found to increase as graft level increased. Surface profile of representative films was also investigated by viewing the distribution of elemental nitrogen using SEM‐EDAX. Results indicated that copolymers of 4VP, NVP, and 2VP are considerably different from each other. 4VP‐based copolymers exhibited relatively more homogenous grafting over the surface compared with NVP‐ and 2VP‐based copolymers. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011