bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

AbstractRecent 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

Abstract
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

Abstract
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

Abstract

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

Abstract
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

Abstract

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

AbstractAutomotive 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

AbstractProton 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

Abstract
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

AbstractIn 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

AbstractMany 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

AbstractIn 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

AbstractHigh‐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

Abstract
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

AbstractTo 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

AbstractThe 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

Abstract
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.