bluuebunny/crossref_metadata_2025_split huggingface dataset:
Macrocycles
Authors: Zagal J. H. 
Published: December 2010

AbstractThe catalysis of the reduction of oxygen on supported metal macrocyclics is discussed in terms of electronic interactions of the dioxygen molecules with metal centers that lead to the weakening of the OO bond and to a lowering of activation energy. Correlations between electronic properties of the macrocyclic complexes and activity are also discussed, such as the influence of the redox potential of the metal center in the electrocatalysis. The overall 2‐ versus 4‐electron reduction mechanisms on metallo‐macrocyclics are discussed including the different approaches used in the literature to achieve 4‐electron reduction mechanisms by designing face‐to‐face binuclear complexes, polymerized metal complexes or macrocycles substituted with peripheral redox groups. The systems that are more promising for practical applications, such as the heat‐treated carbon supported catalysts, are discussed in detail and with explanations on how these pyrolyzed catalysts have higher activity and better stability compared with other supported macrocyclic systems. The requirement for the existence of the “burned‐in” MN4moiety also known as the “super‐site” in heat‐treated catalysts is emphasized. Heat‐treated carbon supported macrocyclics catalysts are not poisoned by methanol and in principle they can be suitable for low‐temperature acid electrolyte fuel cells. The methods of preparation of supported catalysts include: (a) modified electrodes by adsorption or surface modification; (b) heat‐treated carbon supported catalysts; (c) influence of carbon surface modification and electrodes prepared by polymerized macrocyclics; and (d) methanol tolerance and comparison of the activities with platinum‐based electrocatalysts.
O2‐reduction at high temperatures:SOFC
Authors: Ivers‐Tiffée E. , Weber A. , Schichlein H. 
Published: December 2010

AbstractIn this chapter the general requirements for solid oxide fuel cell (SOFC) cathodes and several ways of implementing them are described. The transport properties of cathode structures based on different perovskite type metal oxides are the main focus. Various possible reaction pathways for the two classes of cathode material, i.e., electronic conducting and mixed ionic/electronic conducting cathodes, are discussed. The importance of the microstructural properties of the cathode/electrolyte interface is illustrated. The dependence of cathode performance on the interaction between cathode composition and interface structure is demonstrated by i/v‐characteristics of different cathode/electrolyte configurations. A literature review of models for the high temperature oxygen reduction is given. The elementary reaction steps used in the different models are classified into three categories: surface reaction, surface and bulk diffusion, and incorporatied into the electrolyte. A general approach for modeling and simulation of the electrical response of the oxygen reduction process is presented by using a two‐step model accounting for surface adsorption of oxygen and charge transfer of oxygen into the electrolyte in the vicinity of the three phase boundary.
Formic acid oxidation
Authors: Feliu J. M. , Herrero E. 
Published: December 2010

Abstract
Formic acid oxidation on platinum is a structure‐sensitive reaction that takes place via a mechanism with two paths. One of the paths leads to the formation of CO (poison intermediate), which adsorbs strongly on to the surface and hinders the oxidation of formic acid through the active intermediate. Both paths are structure sensitive. Activities for both paths are parallel; a high activity for the path through the active intermediate is usually associated with a high activity for poison formation. The modification of the surface with adatoms has been used to increase catalytic activity and/or diminish the poisoning of the platinum surfaces. The behavior of the adatoms on the different platinum surfaces is discussed and a model for the actuation of the adatoms is given.
Methanol effects on theO2reduction reaction
Authors: Gilman S. , Chu D. 
Published: December 2010

AbstractThe present most advanced technology for direct methanol fuel cell systems is based on proton exchange membrane technology. The membrane/electrode assembly is normally comprised of a sulfonated perfluorinated hydrocarbon membrane that acts as both the electrolyte and mechanical support for the anode and cathode electrodes. The cathode is usually fabricated using Pt black or Pt supported on carbon as the electrocatalyst. The operating temperature is usually well below 100 °C, to minimize vaporization of fuel and water. While this construction offers many advantages, including an invariant, immobile high conductivity electrolyte and very compact cells and cell stacks, it presents disadvantages relating to high permeability of methanol through present available membranes. Methanol permeating through the membrane is usually reported as completely oxidized at the Pt‐based cathode. Permeation of methanol occurs by a combination of thermal diffusion and osmosis and can be equivalent to upwards of 100 mA cm−2of methanol oxidation current. From the practical point of view, methanol permeation is objectionable because it both wastes fuel and depresses the cathode potential.At the oxygen/air cathode, oxygen reduction and methanol oxidation occur simultaneously. For a simple “mixed potential” effect, the two partial currents would have the same magnitude at any potential as they would if fed to the electrode separately. That is, the cathodic overvoltage would increase to an extent corresponding to an increase in current density corresponding to the partial methanol oxidation current. In the actual practical situation, there is an additional increase in overvoltage of ∼50 mV that appears to correspond to poisoning of the electrocatalyst by methanol adsorbate.There are a number of approaches that have been pursued to reduce the “methanol effect”. Using dilute fuel and operating a fuel cell at high anodic current densities (causing some concentration polarization) can greatly reduce permeation, but with an increase in system complexity. A number of new or composite ion membranes have been explored. So far, reduced permeation has also been accompanied by lower conductivity, poorer mechanical strength or higher electrode polarization. Perhaps the most promising approach involves the development of methanol tolerant electrocatalysts, that are based on porphyrins, chevrel‐phase compounds and other transition metal chalcogenides, some of which appear to approach the catalytic efficiency of Pt. Establishment of long‐term chemical/electrochemical stability of such materials could provide the best solution to the problem of “methanol effects”.
Oxidation ofC2molecules
Authors: Petrii O. A. 
Published: December 2010

AbstractThe nature of processes responsible for open‐circuit potentials in solutions containing C2 compounds is considered. The peculiarities of adsorption of C2 compounds on electrode surfaces are reviewed, and also the specific features of electrocatalytic oxidation of these reactants under nonsteady state and steady state modes. The principles of choice of electrode materials for effective electrooxidation of C2 molecules are formulated, and the prospects of practical applications of these reactions are discussed.
Oscillations and other dynamic instabilities
Authors: Krischer K. , Varela H. 
Published: December 2010

AbstractVirtually any electrochemical reaction exhibits temporal or spatial instabilities, such as bistable reaction rates, spontaneous rate oscillations and the formation of propagating potential waves, in some ranges of the external parameters. Most of these instabilities are associated with a negative real faradaic impedanceZF(ω), whereby two cases are distinguished: Either the stationary polarization curve possesses a negative differential resistance, i.e.,ZF(ω = 0) < 0, orZFis negative only in a certain interval of finite perturbation frequencies ω. The first type of systems may oscillate if a fixed voltage is applied to the cell (i.e., under potentiostatic control), the second class exhibits oscillations under potentiostatic and galvanostatic conditions. Most of the oxidation reactions of small organic molecules belong to the second class. We first discuss general properties of systems falling in either of these two categories. Then we present a survey on temporal and spatial nonlinear phenomena observed in fuel cell relevant electrocatalytic reactions and deduce the reaction steps essential for the instability in the individual reactions.
Hydrogenation reactions
Authors: Pastor E. , Rodríguez J. L. 
Published: December 2010

Abstract
Hydrogenolysis reactions (at alcohols) and hydrogenation of unsaturated groups (double and triple bonds in hydrocarbons and alcohols) are analyzed by combining data obtained applying traditional electrochemical methods, such as long‐term electrolysis followed by chromatographic studies, with results from differential electrochemical mass spectrometry (DEMS). This technique allows the detection not only of the gases evolved in these processes, but also of the volatile products formed. Thus, for example, the formation of propanol and allyl alcohol during the electroreduction of propargyl alcohol at platinum was established from DEMS, while previous studies only suggested this possibility as an explanation for the current efficiency of about 60–70% calculated for the gas production. Moreover, the formation of each reduction product can be recorded independently with time, choosing appropriate mass to charge values for these compounds, as shown for benzyl alcohol at platinum and palladium. Finally, the introduction of single crystals to the electrochemical systems provides a new tool for the study of the influence of the structure on the reactivity towards the reduction of these molecules. The hydrogenation of ethene, ethyne or benzene at different oriented surfaces serves as illustration of this effect.
CO2‐reduction, catalyzed by metal electrodes
Authors: Hori Y. 
Published: December 2010

AbstractThe electrochemical reduction of CO2proceeds in aqueous electrolytes with large overpotential, since the first step of the CO2reduction, i.e., CO2−anion radical formation, requires highly negative potential. The product distribution from the CO2reduction depends greatly on the electrode metal. Cu yields CH4, C2H4and alcohols; Au, Ag and Zn give CO as the main product; Pb, Hg, In, Sn, Cd and Tl form HCOO−; Ni, Fe and Pt do not reduce CO2whereas H2evolves from the electrolysis of H2O. The reason is rationalized in terms of the adsorption of CO2−anion radical on the electrode metals. The CO2reduction at the single crystal electrodes of Cu and Pt metals is summarized, and the mechanism of the hydrocarbon formation at Cu electrode is discussed in detail. The rate of CO2reduction is enhanced by increased transport of CO2to the electrode; such as the solid polymer electrolytes, the gas diffusion electrodes, the electrolyses under high pressure or in nonaqueous electrolytes.
Natural gas for power generation and the automotive market
Authors: Theisen T. 
Published: December 2010

Abstract

This article demonstrates that natural gas must be counted among the sustainable energy sources. What is more, natural gas acts as a bridge to a supply system based on hydrogen. The significance of natural gas in the primary energy mix of industrialized countries will only increase as time goes on. Increasing competition in the energy markets under the heading of liberalization will lead on the one hand to the development and use of highly efficient energy converters like fuel cells, for example, and on the other hand political pressure with an eye to the European CO
2
reduction targets will give clear impulses in this direction. This article also demonstrates the advantages and opportunities of using natural gas as a low carbon fossil fuel in order to achieve these targets. Above and beyond this, the role of natural gas in the energy intensive domestic, industrial and transportation sectors will be fully examined. In particular, the influence of fuel cell technology in these areas of application will be presented and the significance of natural gas as a fuel examined from technical and economical points of view.
Synthetic hydrocarbons as long‐term fuel option
Authors: Price J. G. , Jager B. , Dancuart L. , Keyser M. J. , van der Walt J. 
Published: December 2010

Abstract
While debate still rages over what the long term primary fuel source for fuel cells will be, there is no doubt that hydrocarbon fuels have a major advantage in terms of infrastructure and energy density compared to all other options. The disadvantage of these fuels lies in the fact that oil‐derived fuels are relatively expensive to convert into hydrogen and tend to be aggressive towards the fuel processor (reformer) and fuel cell catalysts. Synthetic hydrocarbon fuels, produced via the Fischer–Tropsch (FT) synthesis provide a sulfur‐ and aromatic‐free alternative to conventional hydrocarbons which are consequently more benign towards fuel cell catalysts. Currently, the technology is on a fast pace towards full commercialization, with the expectation that as much as 1 million barrels per day of capacity could be on line by the end of this decade, contingent on world economic conditions. Fuels produced using the gas‐to‐liquids technology, particularly when utilizing associated gas sources, provides an environmentally sound method of producing liquid fuels. Gasification of solid and liquid waste products may also be beneficially used to produce the synthesis gas required for the FT synthesis.
High pressure storage
Authors: Funck R. 
Published: December 2010

Abstract
The use of hydrogen as an automotive fuel requires storage systems that have inherent safety as well as volumetric and gravimetric efficiency. While the market for composite pressure vessels is continuously growing, metallic and hoop wrapped metallic pressure vessels are more and more substituted by fully wrapped metal liner and all‐composite pressure vessels, which bring weight savings of up to 75%.
Different types of composite pressure vessels are described in the following. Also equations for the estimation of the density of hydrogen gas and its energy content at different pressure levels are given. The description of design principals of pressure vessels is followed by the overview of manufacturing techniques and filament winding theory underlined by some typical examples taken from actual manufacturing. Future development of high pressure storage is also given within this contribution.
Liquid hydrogen technology for vehicles
Authors: Wolf J. 
Published: December 2010

Abstract

The paper provides information about the advantages of using of liquid hydrogen (LH
2
) compared with compressed gaseous hydrogen gas. The necessity of specially designed tank systems to fit the restricted available space within the vehicles is highlighted. The hermetic clean break coupling for the filling/refilling of cryogenic fuel systems, which enables safe and easy handling, extremely short filling and coupling times as well as a high rate of filling sequences, is presented. The indispensable basic element of the world's first public LH
2
filling station in Munich airport — the robot application of this coupling — is illustrated.
Aqueous borohydride solutions
Authors: Suda S. 
Published: December 2010

Abstract

This chapter describes the aqueous borohydride solution as a hydrogen storage system. Its applications for supplying gaseous hydrogen to the polymer electrolyte membrane fuel cell are introduced. The contribution describes the borohydride system as a liquid hydride and consists of the following four main topics: (i) borohydride systems as a gaseous hydrogen source; (ii) production of borohydride from borax or a mixture of borate and sodium hydroxide; (iii) hydrogen generation system; and (iv) protide (H
−
) in BH
4
−
complex ions as the source of two electrons per protide and its application to a new type of fuel cell named the borohydride fuel cell.
Catalyst development and kinetics for methanol fuel processing
Authors: Peppley B. A. , Amphlett J. C. , Mann R. F. 
Published: December 2010

Abstract

The reactions involved in methanol fuel processing are discussed. It is stated that the direct reaction of methanol and steam to form carbon dioxide and hydrogen is the key hydrogen producing reaction. Catalysis by Cu/ZnO/Al
2
O
3
is described in general terms. The literature on the kinetics of methanol–steam reforming is described in detail. Early kinetic models that were adequate for a limited range of operating conditions are discussed. The importance of understanding the surface reaction mechanism for developing models that are valid over wide ranges of conditions is described, followed by a description of the evolution of surface mechanisms for the process leading to a comprehensive kinetic model. The usefulness of this mechanistically‐based model is described in detail. The relative importance of the water–gas shift reaction, in particular, is revealed. Subsequently, the limitations and operating problems associated with Cu‐based catalysts are discussed. Both deactivation and pyrophoric behavior are cited as major problems. Finally, alternatives to Cu‐base catalysts are discussed. These include Ni‐hydrotalcites and Pt on ceria. Although these catalysts have lower activity than Cu‐based catalysts at temperature below 300 °C, their thermal stability at temperatures as high as 390 °C makes them more practical in fuel processors for methanol‐fuelled fuel cell systems.
MixedPOX/steam‐reforming reactor design considerations
Authors: Reinkingh J. , Petch M. 
Published: December 2010

AbstractProton exchange membrane fuel cell (PEMFC) system developers for automotive applications are looking to generate hydrogen on‐board a vehicle. Methanol is relatively easy to reform into a hydrogen‐rich stream at moderate temperatures. Since methanol is a liquid, it is easy to handle and it has a good energy density.The two processes applied to generate H2from methanol are steam reforming and mixed partial oxidation (POX)/steam reforming (SR). In a mixed POX/SR reformer system reactor the oxidation and steam reforming reactions all take place in the same reactor. This type of reforming is also often referred to as autothermal reforming.A mixed POX/SR reformer system reactor holds several advantages over a SR reformer system reactor. These include shorter start‐up time, excellent transient performance and a compact reactor design. The efficiency of a mixed POX/SR fuel processor, if designed properly, should be similar to that of a steam reformer system.Mixed POX/SR fuel processors have similar challenges to SR systems, which are heat integration, catalyst optimization and durability. The disadvantages are the dilution effect of the nitrogen from the air and the parasitic power loss of supplying the air when operated at pressure. Mixed POX/SR reformers are more suitable for near ambient pressure operation.
Steam reforming,ATR, partial oxidation: catalysts and reaction engineering
Authors: Rostrup‐Nielsen J. R. , Aasberg‐Petersen K. 
Published: December 2010

AbstractThis chapter presents steam reforming and partial oxidation as a means for converting a hydrocarbon feedstock into a hydrogen containing gas for fuel cells. The different reactor concepts, choice of catalyst and causes of deactivation are described together with reaction mechanisms. The advantages and disadvantages of the alternatives are discussed with emphasis on efficiency, operating conditions, type of fuel cell, and simplicity.
Sulfur removal methods
Authors: Hidalgo‐Vivas A. , Cooper B. H. 
Published: December 2010

Abstract

Hydrogen production processes, e.g., steam reforming and partial oxidation, begin with a pretreatment section where a sulfur removal method is employed to prepare the feedstock. The characteristics of possible reforming fuels, i.e., liquefied natural gas, liquefied petroleum gas, naphtha and diesel are discussed in a refinery context. Sulfur compounds present in crude oil fractions are divided into different classes. Some exhibit a very low reactivity, which makes them more difficult to desulfurize, and which significantly impacts the achievement of ultra‐low sulfur levels. The improved design of efficient hydrodesulfurization processes is based on the understanding of the process chemistry. In the case of a feedstock with low sulfur content, removal of sulfur can be achieved by absorption processes, e.g., absorption on a zinc oxide catalyst bed. In the case of heavier feedstocks or feedstocks with a high sulfur content, a first step consisting of a hydrodesulfurization process becomes necessary. The process conditions, i.e., temperature, pressure, space velocities, catalysts, etc. are determined by the type of feedstock to be treated. The catalysts most generally used for hydrotreatment consist of cobalt and molybdenum oxides or nickel/molybdenum compounds, both supported over alumina. CoMo and NiMo catalysts desulfurize the most refractory compounds through different desulfurization routes, thus the choice of catalyst will be a function of the type of feedstock and process conditions. It is required that the hydrogen sulfide produced by the desulfurization reactions is removed. Options used to remove H
2
S from the system include the use of zinc oxide absorption, amine wash treatment or both.
Membrane reactor concepts
Authors: Wieland S. , Melin T. 
Published: December 2010

Abstract
Fuel cell powered vehicles with on‐board reforming need compact and lightweight components. A membrane reactor that combines hydrogen permeable membranes with a methanol steam reformer promises considerable weight and space savings. Its dense metal membranes produce high‐purity hydrogen over a wide range of pressures and loads. The selective removal of hydrogen yields methanol and CO conversions that are higher than the equilibrium conversion in a conventional reactor. Results with three different metal membranes in a membrane reactor for steam reforming of methanol are presented. A mathematical model accurately describes the measured performance of the membrane reactor and allows predictions for other values of the process parameters.
Autothermal reforming
Authors: Baumann F. , Wieland S. , Himmen M. , Agar D. W. 
Published: December 2010

AbstractAutothermal reforming (ATR) combines endothermic (viz. steam reforming) with exothermic (viz. partial oxidation) processes. This chapter comments on the differences between the various reforming technologies, their advantages and drawbacks in different application areas and on the use of the terminology ATR as it is used in the literature. The influence of reaction parameters like air stoichiometry, steam content and preheating temperature on the autothermal process is discussed based on simulations and experimental results. An overview of the development of autothermal processes starting in the 1970s up to recent progress in this field is given.