bluuebunny/crossref_metadata_2025_split huggingface dataset:
The electrode–electrolyte interface
Authors: Hamnett A. 
Published: December 2010

Abstract
This chapter describes the structure of the electrochemical double layer formed between an electronically conducting electrode and an ionically conducting electrolyte. The origin of the potential difference across this double layer is explained, and methods for calculating this potential in simple cases are discussed, beginning with the Goüy–Chapman model and incorporating oriented solvent molecules and specifically adsorbed ions at the electrode surface. Some more recent calculational approaches are reviewed in order to shed light on the normal classical models.
Ideal and effective efficiencies of cell reactions and comparison to carnot cycles
Authors: Vielstich W. 
Published: December 2010

Abstract
Data for the ideal efficiency of energy conversion in fuel cells, as calculated from thermodynamics, are listed for several fuel cell reactions. In order to obtain effective efficiency, potential drops at ohmic and kinetic resistances have to be considered. The electric power of a fuel cell is compared with the maximum obtainable work of a heat engine, using the same fuel. Due to Carnot factor limitations of heat engines, fuel cells show advantages over a wide range of power capacities. In addition, conversion efficiencies by using coal as the primary energy source are compared for the final use in fuel cells, secondary batteries or internal combustion engines.
Kinetics of electrochemical reactions
Authors: Hamnett A. 
Published: December 2010

Abstract

This chapter explores the dependence of the
rate
of electrochemical reactions on the potential difference accommodated in the double layer. The concept of overpotential is introduced, and the theory of electron transfer at the electrode–electrolyte interface described. The derivation of the Butler–Volmer equation is shown to depend on the
reorganization
energy of the fundamental electrochemical reaction being large compared to the electrical energy associated with the electron transfer process across the interface. The pre‐exponential expression in the Butler–Volmer equation, the
exchange current
, is shown to depend on the fundamental kinetics of the electrochemical reaction, and some simple examples are given.
High temperature fuel cells
Authors: Divisek J. 
Published: December 2010

Abstract
The principle of energy conservation determines the energy balance equation which can be generally formulated as the sum of single rates of energy input and output, energy production and accumulation. In a fuel cell, the balance takes into account the thermal and the electrical energy. There are three modes of heat transfer process occurring in a fuel cell: conduction, convection and radiation. The fundamentals of these processes are discussed together with the heat transfer occurring with the change of state, such as evaporation, condensation and additional chemical reactions.
The general energy balance equation is analyzed with respect to the heat sources, energy balances for single phases, boundary conditions and parameter definition. Also an approach for the delocalization of reaction entropy in fuel cells is given.
Based on the general heat transfer equations, water and heat management for low temperature fuel cells (hydrogen and direct methanol) is discussed considering the cell structure, current density and temperature distribution.
Heat transfer in high temperature fuel cells is extremely important for system evaluation. Heat management for high temperature fuel cells (molten carbonate and solid oxide) is analyzed. Heat generation in high temperature fuel cells is strongly influenced by chemical reactions, such as methane/water reforming. Thermodynamic analysis and reaction kinetics of the reforming reaction are presented. A performance analysis of molten carbonate fuel cells, planar and tubular solid oxide fuel cells is made considering the cell geometry, current density and temperature distribution. Finally, heat removal for cogeneration in solid oxide fuel cells is discussed.
Air‐cooled
PEM
fuel cells
Authors: von Helmolt R. , Lehnert W. 
Published: December 2010

Abstract
Proton exchange membrane (PEM) fuel cells operated with hydrogen are usually operated at a voltage of around 0.7 V. This means that power conversion in a PEM fuel cell usually has an efficiency of about 50%. Therefore, a cooling medium has to flow through the bipolar plate and the heat has to be removed by convection of this medium. Most PEM fuel cells are cooled with de‐ionized water. Air cooling can be an option especially for mobile and portable applications. As the complete liquid‐cooling loop is no longer necessary, an air‐cooled system might be much simpler. Advantages and disadvantages of air‐cooled stacks will be discussed in the article. Furthermore some examples of air‐cooled stacks will be presented.
Direct methanol fuel cells (DMFC)
Authors: Hamnett A. 
Published: December 2010

AbstractThe basic principles of operation of the direct methanol fuel cell (DMFC) are described, and ways in which this cell can be realized in practice reviewed. There are several serious problems that currently make it difficult to fabricate practical DMFCs; these include poor performance at both anode and cathode, degradation of the commonly used poly1fluorosulphonic acid membranes and permeation of methanol from anode to cathode cell compartments. Approaches to each of these problems are enumerated, and molecular insights and recent experimental data are brought together to provide an up‐to‐date account of the DMFC and its prospects.
Electrode potential and double layer
Authors: Trasatti S. 
Published: December 2010

Abstract
This chapter describes the structure of electrode/solution interfaces and the origin of the electrode potential. Equilibrium conditions are considered. The energy of particles in a phase, the equilibrium between phases and the origin and the physical significance of electrode potentials are discussed. Two main systems are considered: metal/solution and oxide/solution interfaces. Potential of zero charge for the former and point of zero charge for the latter are defined. The structure of the interface and its dependence on a number of parameters such as electrode potential, crystallographic orientation, nature of the solid, etc. are discussed. The fundamental importance of the interaction between the solid and the solvent and its influence on adsorption phenomena is stressed.
Reaction mechanism and rate determining steps
Authors: Trasatti S. 
Published: December 2010

AbstractThe chapter provides the fundamentals on electrochemical kinetics: departure from equilibrium and components of cell potential difference (overpotentials, ohmic drop); additional effects due to the stability and its significance; various types of reaction barriers; description of the parameters of electrode kinetics and how Tafel slopes and reaction mechanisms are interrelated; dependence of Tafel slope on intermediate coverage. The case of multiple Tafel slopes is also discussed.
Theory of electrochemical outer sphere reactions
Authors: Leiva E. , Sánchez C. 
Published: December 2010

Abstract
Different theoretical aspects of electrochemical outer sphere reactions are briefly discussed. This introductory overview includes classical models based on transition state theory, quantum mechanical models that employ first‐order time‐dependent perturbation theory as well as more generalized approaches that are suited for the study of both adiabatic and non‐adiabatic reactions. Stochastic aspects as well as recent computer simulations are also addressed.
Vibrational spectroscopy
Authors: Rodes A. , Pérez J. M. , Aldaz A. 
Published: December 2010

Abstract
Fundamental and experimental aspects of infrared spectroscopy techniques are reviewed in connection with their application to the in situ study of the processes taking place at the metal/solution interphase. Advantages and drawbacks of external and internal reflection experiments are discussed in some detail. Then, typical applications are described, with special emphasis on the spectroscopic characterization of adsorbate layers. The feasibility of gaining structural information from the infrared spectra of adsorbed species at different substrates, ranging from adatom–modified single crystal electrodes to nanoparticles is pointed out. New developments are discussed, including the application of step‐scan interferometry to the kinetic study of fast adsorption processes at the electrode surface.
EXAFS
,
XANES
,
SXS
Authors: Adžić R. R. , Wang J. X. , Ocko B. M. , McBreen J. 
Published: December 2010

Abstract

This chapter describes the application of in situ surface X‐ray scattering (SXS) and X‐ray absorption spectroscopy (XAS) to the problems of fuel cell electrocatalysis. It is shown that SXS is well suited for studying single crystal electrode surfaces during electrocatalytic reactions. The structure of surfaces and surface adlayers which exhibit long range order can be probed with high accuracy and a quantitative measure of potential induced structural phase transitions can be obtained. XAS is sensitive to both structural and chemical information and can be applied to polycrystalline electrocatalysts under in situ conditions. A great advantage is that XAS is element‐specific, and this permits investigation of the chemical environment of a constituent element in a composite material such as alloy catalysts. Since XAS probes only short‐range order, it can provide structural information on amorphous materials, liquids, gases, adsorbed monolayers, as well as hydrated ions and complexes in aqueous solution. A major advantage of XAS in the study of electrocatalysts is its ability to probe the
d
states of Pt catalysts.
Combinatorial catalyst development methods
Authors: Mallouk T. E. , Smotkin E. S. 
Published: December 2010

AbstractCombinatorial chemistry provides a means of rapidly screening electrocatalysts for use in fuel cells and related applications. The screening methods that have so far been applied to electrocatalyst arrays include indirect fluorescent detection, steady‐state voltammetry, chronoamperometry, and scanning electrochemical microscopy. Several different types of anode and cathode electrocatalysts for polymer electrolyte membrane fuel cells have been studied by these techniques. Heuristic models based on mechanistic and spectroscopic studies of fuel cell catalysis are useful in guiding these searches for new catalyst compositions, and detailed studies of the catalysts already discovered can help to refine or augment these models. One of the outstanding challenges remaining in this area is to find ways to match more closely the synthesis/screening conditions of array catalysts with those of bulk catalysts used in real fuel cells.
Numerical simulations of electrocatalytic processes
Authors: Koper M. T. M. 
Published: December 2010

Abstract

Recent developments in the computer simulation of electrocatalytic processes are discussed. The type of computer simulation chosen for a particular application depends on the time scale of the process and the level of molecular detail desired. Quantum‐chemical electronic structure calculations utilizing the density functional formalism give information about the details of the chemical bonding of molecules at surfaces. Application of the bonding of carbon monoxide to transition metal surfaces and alloys is described, including the role of the electric field. The link to macroscopically measurable kinetics, like voltammetry, can be made by resorting to Dynamic Monte Carlo methods. In this method, reaction events are mapped on to a lattice‐gas model of the catalyst surface and the statistical mechanics is solved
exactly
by Monte Carlo simulation algorithms. The reactant parameters can either be obtained from first‐principles quantum chemical calculations, or be adjusted so as to mimic as closely as possible the experimental results. An example of this method as applied to the oxidation of CO on platinum–ruthenium alloys is discussed.
The hydrogen electrode reaction and the electrooxidation ofCOandH2/COmixtures on well‐characterizedPtandPt‐bimetallic surfaces
Authors: Marković N. M. 
Published: December 2010

AbstractInterrelationships between the kinetics of fuel cell reactions and the structure/composition of anode catalysts are reviewed. Model systems like Pt single crystals and well characterized Pt(hkl)/Pd and Pt3Sn(hkl) bimetallic surfaces are used to establish a link between the macroscopic kinetic rates and thermodynamic properties of the reacting system and the microscopic level of understanding of the bonding and reactivity of the reaction intermediates and spectator species. The results show that the hydrogen reaction is a structure sensitive process, with Pt(110) being an order of magnitude more active than either of the atomically “flatter” (100) and (111) surfaces. The difference in the activity at the crystal face is attributed to the structure sensitive adsorption of hydrogen (Hupd) and hydroxyl anions (OHad) and the effect these species have on the formation of an active intermediate (Hopd). The significant differences of the hydrogen reaction in alkaline versus acid electrolytes are thought to arise due to the presence of OHad, even close to the reversible potential of the hydrogen reaction in the alkaline electrolyte. The hydrogen reaction on Pt(hkl) modified by pseudomorphic Pd (sub)monolayers shows “volcano‐like” behavior, having the maximum rate on Pt(111) modified by 1 ml of Pd. The physical model based on differences in the adsorption energies of Hupdand Hopdon Pd vs. Pt is used to rationalize the catalytic activity of Pd atoms. For the Pt(111)/CO system, a remarkable difference in both activity and stability of thep(2 × 2)–3CO ordered structures is observed between alkaline and acid solutions. The pH‐effect is explained as the pH‐dependent adsorption of OHad, which starts in the Hupdpotential region at defect sites. The oxidation of H2in the presence of CO occurs concurrently with CO oxidation on Pt and Pt bimetallic surfaces. The PtSn(111) system is used to demonstrate that both the bifunctional effect and the ligand effect contribute to the influence of Sn on the CO oxidation rate and for H2oxidation process in the presence of CO.
Oxidation reactions in high‐temperature fuel cells
Authors: McEvoy A. J. 
Published: December 2010

AbstractThe high temperature fuel cell anode is activated thermally and therefore does not require noble metal catalysts to maintain the oxidation kinetics. Consequently, the high temperature devices are fuel‐tolerant, so an important advantage for their commercial future is the adaptability to commercial fuels. At most a simple pre‐reforming is all that is required to provide an acceptable fuel stream.The anode is part of an overall electrochemical system in which the other principal components are the oxygen ion source, either the molten carbonate electrolyte in which the oxygen carrier is the carbonate ion, CO32−, or the solid electroceramic electrolyte in which oxygen ions are mobile, and the gas phase fuel stream. Reactions are generally considered as taking place at a three‐phase boundary, which for low polarization must be delocalized to form a volumetrically functioning anode by appropriate materials selection. Concentration overpotential effects are due to diffusion problems for the ingress of the fuel gas, or inhibition of discharge of reaction products.The functioning of the current state‐of‐the‐art cermet anode is described, as are the considerations motivating the search for new and innovative anode materials, particularly metal oxides and perovskites; in principle these should permit direct oxidation of at least the lower hydrocarbons without restriction by carbon formation and other degradation mechanisms.Operation of anodes at lower temperatures is also a motivation for current development work, so that the oxidation kinetics are maintained at a lower level of thermal activation of the system.
Poisons for the
O
2
reduction reaction
Authors: Paulus U. A. , Schmidt T. J. , Gasteiger H. A. 
Published: December 2010

Abstract

We reviewed the influence of various kinds of impurities on the oxygen reduction reaction mainly on platinum as electrocatalyst. Our discussion includes data obtained from work with smooth polycrystalline platinum electrodes or platinum single crystals, data obtained from supported catalysts and as far as available results obtained with membrane electrode assemblies in fuel cells. It is shown that the oxygen reduction reaction activity can be affected significantly by the presence of contaminants which may or may not change its reaction pathway (transition from a 4e
−
reduction to a 2e
−
reduction or vice versa).

The effect of anionic and cationic (mainly copper) additives is discussed as well as the influence of the presence of methanol (representing the class of organic contaminants). Throughout this discussion, it becomes evident that the various additives affect the oxygen reduction reaction in different ways. Nevertheless, generally it can be stated that the efficient usage of the electrocatalytic oxygen reduction reaction at a platinum catalyst results in a high level of purity during all processes connected with fuel cell assembly and operation.
O
2
‐reduction at high temperature:
MCFC
Authors: Hemmes K. , Selman J. R. 
Published: December 2010

Abstract

Oxygen reduction in molten carbonate is discussed in relation to the molten carbonate fuel cell. The melt chemistry of molten carbonate is found to be crucial in understanding the possible reaction mechanism and the dissolution problems of the cathode. Using concepts form linear algebra a complete set of equilibria describing the melt is constructed, which is used to derive the relative concentrations of species in the melt and possible reaction mechanisms. Experimental results are critically reviewed in the light of the theoretical predictions. Based on the obtained insight in the fundamental processes, research directions are indicated for minimizing cathode dissolution and cathode polarization, including a radical new concept of a MCFC with a separate CO
2
channel.
Methanol and formic acid oxidation on ad‐metal modified electrodes
Authors: Waszczuk P. , Crown A. , Mitrovski S. , Wieckowski A. 
Published: December 2010

AbstractThis chapter describes modification of platinum and some other noble metal electrodes for enhanced catalytic oxidation of methanol and formic acid. The modification was carried out by electrochemical addition of submonolayer‐to‐monolayer quantities of noble metals to noble metal substrates, with the primary focus on the use of spontaneous deposition. In contrast to underpotential deposition (UPD), the term noble metal deposition on noble metal substrates (NM/NM) is introduced to cover high reactivity model and real electrodes for fuel cells. We begin with providing a brief description of the basic mechanistic pathways for methanol and formic acid oxidative decomposition on platinum. Subsequently, we review the modified electrodes utilized for the study of methanol oxidation, such as platinum/ruthenium, platinum/osmium (and ruthenium/platinum for enhanced CO tolerance), and palladium/platinum and gold/palladium electrodes for formic acid oxidation. The Pt/Ru electrodes are reviewed most comprehensively as the Pt/Ru mixed‐metal materials are used as an anode in the direct oxidation methanol fuel cell. Despite progress recently made in the specific catalytic categories interrogated in this chapter, research is still needed to establish a solid and comprehensive base for preparation of new catalytic materials via the rational rather than trial and error principle; the latter has exhausted its utility many years ago.
Hydrazine fuel cells
Authors: Kohnke H. 
Published: December 2010

Abstract

Hydrazine as an oxidant for fuel cells is important for niche applications, as it can be stored in simple lightweight containers. In addition, their energy density is high — the fuel cells can be optimized for long‐term operation without any service. Hydrazine can be converted to hydrogen and nitrogen in an external reactor or the hydrazine is added to the electrolyte of the fuel cell and converted at special hydrazine electrodes. The catalyst for these electrodes is a modified nickel catalyst. Alsthom has shown the high power density (2 kg kW
−1
) of this fuel cell type in submarines.
Electrochemical supercapacitors and their complementarity to fuel cells and batteries
Authors: Conway B. E. 
Published: December 2010

Abstract

In recent years, so‐called supercapacitors have been developed providing specific capacitances on the order of 50–100 Farads g
−1
of high surface area substrates, e.g., carbon powders, fibers or aerogels, and some transition‐metal oxide films having specific real areas up to ca. 2000 m
2
g
−1
. The capacitance of carbon‐based devices originates from the double‐layer capacity of the carbon/liquid electrolyte interfaces, giving rise to a high degree of reversibility of the charging/discharging processes, leading to perceived operability at large power densities. The large achievable specific capacitance provides systems for substantial charge and electrical energy storage, complementary to that provided by batteries. However, on account of the distributed nature of capacitative,
C
, and ohmic,
R
, components of the impedance, a broad range of
RC
time‐constants arises, corresponding to a power spectrum. Hence high power operation is available from only a fraction of the total capacitance at large current densities or a.c. frequencies, or in short‐time pulses.

An important application of supercapacitors has been envisaged in a load‐leveling role in hybrid configuration with fuel cells or rechargeable batteries. To achieve this, the relation between operable power densities and achievable energy densities of each of the components has to be evaluated in terms of so‐called Ragone plots in a complementary way.
Alternative fuels and prosects — overview
Authors: Ogden J. M. 
Published: December 2010

AbstractContinued reliance on current fuels and end‐use technologies poses serious environmental and energy supply security challenges. Globally, direct combustion of fuels for transportation and heating accounts for over half of greenhouse gas emissions, a significant fraction of air pollutant emissions and about two thirds of primary fossil energy use. A variety of alternative transportation fuels and efficient, low‐polluting vehicle technologies have been proposed to help address these challenges. Vehicle technologies include advanced internal combustion engine vehicles, internal combustion engine/hybrid electric vehicles, battery powered electric vehicles and fuel cell vehicles. Use of lower‐polluting fuels, such as reformulated gasoline or diesel, compressed natural gas, methanol, ethanol, dimethyl ether, Fischer–Tropsch liquids and hydrogen, has been suggested. Fuel cell vehicles are particularly attractive as they have zero or near‐zero tailpipe emissions, offer the potential for near‐zero full fuel cycle emissions and use of diverse primary energy sources. In this chapter, we review the status of alternative fuels for vehicles, with an emphasis on fuel cell vehicles and their fuels. The potential role of fuel cell vehicles in meeting future environmental and energy supply goals is discussed, and fuel strategies for implementing fuel cell vehicles on a wide scale are examined.