bluuebunny/crossref_metadata_2025_split huggingface dataset:
Biochemical fuel cells
Authors: Katz E. , Shipway A. N. , Willner I. 
Published: December 2010

AbstractBiofuel cells transform abundant raw materials into electrical power in the presence of biocatalysts, enzymes, or whole cell organisms. Biomaterials may participate in the biofuel cell activity by either producing fuel substrates or by catalyzing the electron transfer chain between the fuel substrates and oxidizers and the electrodes. Two types of biofuel cell elements are discussed in this review article: microbial‐based biofuel cells and enzyme‐based biofuel cells.Microorganisms may act as microreactors in fuel cells for the generation of the fuel products such as H2or H2S. These fuel products may be generated apart from the biofuel cell and transported to its anodic compartment or, alternatively, may be directly generated in the anodic compartment of the biofuel cell. Different microbial‐based biofuel cells are reviewed in the account.Enzymes are employed as catalysts for the activation of electron transfer chains between the fuel substrate and the anode in the anodic compartment, and between the oxidizer and the electrode in the cathodic compartment. In order to activate the electron transfer cascades between the enzymes and the electrodes, native electron carriers (co‐factors) and artificial electron transfer mediators must be coupled to the biocatalytic transformations. By the nanoengineering of the electrode surfaces with co‐factor/electron‐relay/enzyme assemblies, integrated, electrically contacted, bioelectrocatalytic anodes and cathodes are tailored. Different enzyme‐based biofuel cell configurations are described. The different parameters controlling biofuel cells efficiencies are discussed. The efficiencies of the different biofuel cell configurations are evaluated in terms of the limiting factors and kinetic features of the systems.
Metal/air batteries: the zinc/air case
Authors: Haas O. , Holzer F. , Müller K. , Müller S. 
Published: December 2010

AbstractMetal/air batteries provide high specific energy and consist of inexpensive and environmentally benign materials. They have begun to penetrate the market of portable power sources and offer great promise for transportation applications. In this review, we first discuss the basic aspects of metal/air batteries, then concentrate on the Zn/air system as the most promising metal/air battery. The Zn/air systems have important advantages due to the excellent electrochemical properties of metallic zinc, which include a high overpotential towards hydrogen evolution. This implies that Zn/air batteries with aqueous electrolytes can be electrically recharged, that zinc from spent batteries can be regenerated by electrolysis in aqueous systems, and that mechanically rechargeable Zn/air batteries (arrangements resembling fuel cells) can be realized with aqueous electrolytes.Advances in the development of Zn/air battery components are reviewed and the state of the art of electrically and mechanically rechargeable Zn/air systems is described in detail. An overview of industrial developments in zinc/air battery systems and the nominal performance of available products is included. Practical specific energies in the range of 90–120 Wh kg−1have been reported for electrically rechargeable Zn/air batteries, about twice as much for mechanically rechargeable systems. Significant progress has been made concerning the cyclability of the electrically rechargeable Zn/air system, by utilizing pasted zinc electrodes and graphitized carbon for the bifunctional oxygen diffusion electrodes. Cycle lives in the range of 200–450 cycles have been achieved.
Adsorption — volcano curve
Authors: Trasatti S. 
Published: December 2010

AbstractThis chapter gives a theoretical description of electrocatalysis, providing fundamental aspects not related to particular experimental details. The relationship between intermediate adsorption and reaction rate is discussed. This includes the nature of the solid as well as its surface crystallographic orientation. Primary and secondary effects of the electrode material are illustrated in terms of double layer and chemisorption effects. The origin of volcano curves is demonstrated and their relation to the reaction mechanism pointed out. It is shown that no absolute evaluation of electrocatalysis is possible since the conditions at which electrical effects at the interface vanish are not known.
Theoretical aspects of some prototypical fuel cell reactions
Authors: Leiva E. , Sánchez C. 
Published: December 2010

Abstract

In this section we discuss the application of different theoretical models to two types of prototypical fuel cell reactions. On the one hand, we discuss the electrocatalysis of the electrooxidation C1 (CO, HCOOH and CH
3
OH) molecules. On the other hand, we consider theoretical aspects of the oxygen reduction reaction, with special emphasis in the most recent developments in the theoretical field.
Cyclic voltammetry
Authors: Vielstich W. 
Published: December 2010

Abstract
Cyclic voltammetry (CV) is the most commonly used method in electrocatalysis. The technique offers a first view on electrode/electrolyte systems in the potential window of interest. For most metals and alloys, reproducible results can be obtained after cycling the surface in a base electrolyte and over suitable potential ranges. Cyclic voltammograms of some metal/electrolyte interfaces and some selected charge transfer reactions, of interest in fuel cell electrocatalysis, are presented. The use of CV for investigations, e.g., with ultramicro‐electrodes, rotating electrodes (disc and ring/disc), as well as in combination with online mass spectroscopy and Fourier‐transform infrared radiation spectroscopy, is outlined.
Product analysis
Authors: Torresi R. M. , Wasmus S. 
Published: December 2010

Abstract

Considering interfacial reactions, during the last three decades, surface scientists and electrochemists have made an important effort to develop instrumental techniques in order to study not only the structure and composition of solid interfaces but also to identify product reactions. The need for measuring interfacial events at solid surfaces under ambient conditions has induced the developing of direct in situ methods. In the case of electrochemical processes, which involve mass changes, one of the new techniques introduced in the last two decades is the electrochemical quartz crystal microbalance (EQMB). Results related to anion adsorption and oxidation of small organic molecules are discussed. Other technique which has become a powerful method in electrochemistry is the electrochemical mass spectroscopy, now also directly applicable to fuel cell studies. The technology necessary to design the instrumentation for these investigations is described in depth. Results related to anode oxidation processes are discussed. Initial concerns that the methanol oxidation in a direct methanol fuel cell (DMFC) may not be complete have been shown to be unsubstantiated. Using a Pt/Ru anode and a sufficient excess of water, a yield of CO
2
near 100% is achieved. In contrast, the use of ethanol as a fuel leads to a predominant aldehyde formation under all conditions. The mechanisms of the processes involved are analyzed in the light of these results. Cathode studies showed that the methanol crossover effect in a DMFC is likely a dual mechanism consisting of a non‐electrochemical reaction with additional cathode poisoning. Product identification of oxidation of small organic molecules by using liquid micro‐chromatography or fluorimetry it is also discussed.
Electrochemical impedance spectroscopy
Authors: Ivers‐Tiffée E. , Weber A. , Schichlein H. 
Published: December 2010

Abstract
The fundamentals of electrochemical impedance spectroscopy and its application to the identification of dynamical processes in fuel cell operations are described in this chapter. The scope of the method is seen in the fact, that by applying a small signal perturbation to the cell under test conditions, the relaxation times and relaxation amplitudes of the processes governing cell performance can be identified and targeted for cell optimization. Based on the working principle and the basic measurement set‐up of impedance spectroscopy, measurement arrangements for fuel cells are discussed and specific problems of the method are addressed. Various impedance data analysis techniques are described, including the well‐known complex non‐linear least squares curve fit to equivalent electrical circuit modes as well as the direct deconvolution of impedance data into a distribution of relaxation times. The importance of suitable physical models for the identification of microscopic cell parameters is stressed and an example for the identification procedure is given.
Ex‐situ surface preparation and analysis: transfer betweenUHVand electrochemical Cell
Authors: Hoster H. E. , Gasteiger H. A. 
Published: December 2010

AbstractThe further optimization of electrode materials for fuel cells in laboratory studies offers two main approaches: (i) improving the understanding of the microscopic electrode processes by observation with in‐situ and ex‐situ methods; and (ii) the systematic compositional and structural variation of surfaces to create model electrodes for electrocatalytic measurements.The ultra high vacuum (UHV) environment offers unique possibilities for both surface preparation and analysis and has thus been used extensively in recent electrocatalytical research work. At the same time, methods allowing the in‐situ observation of electrochemical processes has also gone through impressive advances in recent years, and in many cases it has been found that earlier ex‐situ results obtained in UHV needed to be revised due to changes of the electrode surfaces during the transfer into UHV. In the following we will discuss some of the most frequently applied ex‐situ methods in electrocatalytic research and review some of the important aspects concerning the reliability of the resulting data. Utilizing a number of examples, we will demonstrate how such combined UHV electrochemistry experiments can be technically realized, including a discussion of commonly encountered practical problems.We will further point out the advantages offered by the electrocatalytical characterization of UHV designed and UHV characterized model electrodes. In our opinion, this is a very promising approach to UHV/electrochemistry experimentation: on the one hand, the uncertainties due to the transfer between UHV and electrochemical environment are less significant compared to emersion experiments of adsorbed adlayers; on the other hand, well‐established UHV preparation techniques combined with structural characterization tools (atomic force microscopy (AFM)/scanning tunneling microscopy (STM)) provide the possibility of precisely tailoring defined model electrodes. Some examples from research on anode catalysts are given to illustrate this unique capability of UHV electrochemistry setups as powerful tool for the systematic tailoring of model electrodes.
Structure sensitive methods:
AFM
/
STM
Authors: Kibler L. A. , Kolb D. M. 
Published: December 2010

Abstract
In this chapter, the principles of atomic force microscopy (AFM) and mainly of scanning tunneling microscopy (STM) are described. For applications in electrochemistry, in situ operation and the potentialities of STM and AFM are addressed.
STM, a powerful technique for obtaining local structure information of model electrodes on an atomic level and in real space, is highlighted by several case studies, relevant to fuel cell systems: (i) preparation and characterization of well‐ordered noble metal surfaces; (ii) noble metal deposition on foreign substrates; and (iii) nanostructuring of surfaces by the STM tip.
Rotating thin‐film method for supported catalysts
Authors: Schmidt T. J. , Gasteiger H. A. 
Published: December 2010

Abstract

In this chapter, the thin‐film R(R)DE (TFR(R)DE) method is described, i.e., a method for the quantitative evaluation of the electrocatalytic activity of high‐surface area catalysts in a true R(R)DE configuration. The method offers complete catalyst utilization combined with a high reproducibility with respect to the catalyst loading on the electrodes. It is further proven that both catalyst agglomerate and film diffusion effects, respectively, are negligible in the thin catalyst/Nafion layers. That means the thin‐film electrodes can be treated like smooth rotating electrodes with the well‐known hydrodynamics and defined mass‐transport conditions. In other words, kinetic parameters such as kinetic current densities, activation energies, Tafel slopes etc. can directly be determined from the measured current densities
without
applying any mathematical modeling of the mass transport in the catalyst/Nafion layer. Furthermore, this method allows the determination of electrode kinetics under fuel cell relevant mass‐specific current densities of 1–2 A

. The suitability of the TFRDE method is demonstrated by discussing results from different kinetic studies on the oxidation of CO and CO/H
2
mixtures on high‐surface area Pt, PtRu, PtSn and PdAu electrocatalysts. Additionally, it is illustrated how thin‐film electrodes can be successfully used for measurements with a differential electrochemical mass spectrometry (DEMS) setup for the mass‐spectrometrical determination of the electrochemically formed products. In the last section, the adaptation of the TFRDE method for ring‐disk measurements is described. The potential‐ and rotation‐rate independent, well‐defined collection efficiency for the thin film RRDE configuration enables the quantification of the molar fraction of H
2
O
2
produced during oxygen reduction. In general, the TFR(R)DE method can be seen as an easy‐to‐use tool for the screening and characterization of high‐surface area electrocatalysts under low temperature fuel cell relevant conditions.
Reaction mechanisms of theH2oxidation/evolution reaction
Authors: Breiter M. W. 
Published: December 2010

AbstractThe mechanisms of the H2oxidation/evolution are discussed on basis of the classical pathways (Volmer–Tafel reactions and Volmer–Heyrovsky reactions). For simplicity the discussion is given for acidic systems under the assumption of Langmuirian adsorption of the atomic hydrogen, adsorbed on the electrode surface. The modifications necessary for alkaline systems are indicated.The conditions are outlined when one of the pathways is predominant. Control by a single step is then discussed. The possible effect of mass transport is considered. The dependence of the exchange current densities of the individual reactions upon the coverage with atomic hydrogen is derived.The experimental observation that relationships between the logarithm of the exchange current density and the MH bond strength appear to possess a volcano shaped curve is discussed in detail under consideration of how the hydrogen atoms are bonded. The question of which type of hydrogen atoms is involved in the H2oxidation/evolution on platinum metals is briefly considered.Finally, a more complex reaction is treated in which either one or several products are formed. The differences in the kinetics of such reactions to that of the simpler H2oxidation/evolution are pointed out.
Hydrogen evolution reaction
Authors: Lasia A. 
Published: December 2010

AbstractThis chapter presents a review of electrode materials used for the hydrogen evolution reactions and a comparison of their electrocatalytic activities. The introduction presents a brief definition of various thermodynamic water electrolysis potentials. In general, there are two ways to improve the performance of electrode materials: (1) use of electrode materials characterized by higher intrinsic activity i.e., higher exchange current density and (2) use of electrodes characterized by large real surface area. Both methods are used in practice. In this chapter various electrode materials are reviewed: smooth metals, alloys, intermetallic compounds and composites, Raney type materials (Raney Ni, Zn, etc.), oxides, carbides, sulfides, borides, phosphides, amorphous and nano‐crystalline materials etc., Among the most active materials are noble metals, doped Raney‐type alloys, IrO2/Ru2O, sulfides, borides, and Ni/Mo based alloys. Unfortunately, noble metals are very expensive and easily poisoned and their activity decreases with time. Although many materials may still be improved and optimized there is a need to study the detailed mechanism and kinetics of the HER on these materials and the relation between the geometric (surface roughness) and intrinsic electrocatalytic properties.
O2reduction on thePt/polymerelectrolyte interface
Authors: Ota K. , Mitsushima S. 
Published: December 2010

AbstractIn order to attain the high performance of polymer electrolyte fuel cells (PEFCs), the cathode overpotential as well as the resistance of the membrane electrolyte should be reduced. In this paper, the oxygen reduction reaction on Pt has introduced in relation to the quality of the polymer electrolyte. The oxygen overpotential was measured by three electrodes using the mini‐cell method. The mini‐cell has a Pt microelectrode for the working electrode and a dynamic hydrogen electrode for the reference electrode. The contact force at the Pt electrode/membrane interface was measured and controlled by a strain gauge. The solubility and the diffusion coefficient of oxygen in the polymer electrolyte depended on the ion‐exchange capacity of the membrane electrolyte. The diffusion coefficient increased with the decrease of the ion‐exchange capacity. The solubility increased with the increase of the capacity. The dependence of the diffusion coefficient was larger than that of the solubility. The Tafel plot of oxygen reduction current on the Pt showed the two distinct mechanisms for the low and the high overpotential regions. At the low overpotential region, the oxygen reduction reaction proceeded by a 4–electron reaction, the exchange current density had a range from 10−9to 10−8 A cm−2. The dependence of the exchange current density on the ion‐exchange capacity was small.
O2reduction and structure‐related parameters for supported catalysts
Authors: Mukerjee S. , Srinivasan S. 
Published: December 2010

AbstractSupported electrocatalysts starting with the initial patent by Petrow and Allen opened up a new horizon in the field of fuel cell electrocatalysis. Choice of new chemical dispersion methods and choice of carbon support materials led to a quantum jump in the performance of low and intermediate temperature acid and alkaline fuel cells. Among the advantages realized early were: (i) lowering overpotential losses in the activation, mass transport and ohmic polarization regions; (ii) mitigating corrosion and sintering problems; and (iii) increased catalyst utilization and hence decreased cost of noble metals by one or two orders of magnitude. This chapter reviews the fundamental and technological progress in the research on supported electrocatalysts for both phosphoric acid fuel cells (PAFCs) and polymer electrolyte fuel cells (PEMFCs). Early developments in the realization of particle size effects and the interplay between electronic and short range atomic order has been chronicled for the more kinetically difficult oxygen reduction reaction, until the advent of Pt alloy electrocatalysts. The effect of carbon support is also examined from the perspective of possible catalyst‐support synergy both in terms of imparting improved electrocatalysis but also in terms of increased stability (resistance to sintering). Methods of dispersing metals on carbon support are chronicled along with some new developments. In addition, newer techniques involving synchrotron X‐ray techniques are presented in terms of elucidating the true nature of electrocatalysis of oxygen reduction reaction. Some new perspectives on the continued use of these supported electrocatalysts are presented, especially in the emerging field of new synthesis routes for making tailored Pt alloy electrocatalysts.
Oxide‐based
ORR
catalysts
Authors: Goodenough J. B. , Cushing B. L. 
Published: December 2010

Abstract

The reaction pathways on Pt for the oxygen reduction reaction (ORR) in acid and alkaline solution are compared with those on metallic transition‐metal oxides. These reactions are distinguished from those that occur at high temperature at an oxide/air interface of an oxygen‐permeation membrane or the cathode of a solid oxide fuel cell (SOFC). Distinctions are made between polaronic, vibronic, and metallic electronic conductivity in oxides, and the influences of counter cation on the conductivity are pointed out for oxides like the AMO
3
perovskites and A
2
M
2
O
6
O′ pyrochlores, where M is the transition‐metal atom responsible for electron transport. Mixed oxide‐ion and electronic conductors (MIECs) are used as permeation membranes or as cathodes of a SOFC. The criteria for oxide‐ion conductivity in an oxide‐ion electrolyte are reviewed; the same criteria apply for MIECs. The ORR takes place at the cathode of an electrochemical cell, and gas‐diffusion cathodes operating with aqueous electrolytes contain as catalyst Pt or an oxide dispersed on teflon‐bonded, stabilized carbon. Dispersed Pt is compared with Pb
2
[Ir

2−
x

Pb

x

]O
6
O′

1−
y

pyrochlore for an acidic electrolyte. Perovskites are used in alkaline solution, and a bifunctional ORR and oxygen evolution reaction (OER) is used in secondary metal/air batteries. Performance curves for perovskites and pyrochlores are compared. Finally, the criteria for choosing a MIEC as a SOFC cathode or an oxygen‐permeation membrane are given and the performances of several of them are compared.
Chevrel phases and chalcogenides
Authors: Alonso‐Vante N. 
Published: December 2010

AbstractThe underlying background and present development of methanol tolerant electrocatalysts, selective for the oxygen reduction reaction (ORR), are presented. These catalysts are essentially metal‐centered (ruthenium) clusters or cluster‐like compounds. These clusters, partially embedded in a chalcogenide matrix (e.g., selenium) constitute the active center for the electrochemical process ORR. On well‐defined cluster materials, as for example, the so‐called Chevrel phases, based on octahedron clusters [(Mo2/3Ru1/3)6Se8], the ORR electrochemical activity clearly indicated that this phenomenon can be selectively sustained with a four‐electron charge transfer (water formation). This is due to their electronic and geometric characteristics. Hence, clusters work as a pool of charges that can be engaged in a multi‐electron process. Therefore, this family of materials served as a model for the development of novel ones. In this respect, e.g., RuxSey(x ≈ 2,y ≈ 1), tailored from chemical precursors in organic solvents, under mild conditions, shows a high dispersiveness in the nanoscale range. The metallic center shows similar electrochemical properties to those of well‐defined Chevrel phases, thus behaving as a cluster‐like material. The ability of the catalytic center to provide coordination chemistry for reactivity and selectivity via cluster, or cluster‐like compounds is discussed, as well as the trends in the synthesis and the results of tests in half‐cells and in direct methanol fuel cell systems.