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Über dieses Buch

This comprehensive handbook covers all fundamentals of electrochemistry for contemporary applications. It provides a rich presentation of related topics of electrochemistry with a clear focus on energy technologies. It covers all aspects of electrochemistry starting with theoretical concepts and basic laws of thermodynamics, non-equilibrium thermodynamics and multiscale modeling. It further gathers the basic experimental methods such as potentiometry, reference electrodes, ion-sensitive electrodes, voltammetry and amperometry. The contents cover subjects related to mass transport, the electric double layer, ohmic losses and experimentation affecting electrochemical reactions. These aspects of electrochemistry are especially examined in view of specific energy technologies including batteries, polymer electrolyte and biological fuel cells, electrochemical capacitors, electrochemical hydrogen production and photoelectrochemistry.

Organized in six parts, the overall complexity of electrochemistry is presented and makes this handbook an authoritative reference and definitive source for advanced students, professionals and scientists particularly interested in industrial and energy applications.

Inhaltsverzeichnis

Frontmatter

1. Electrochemical Science — Historical Review

Abstract
Electrochemistry developed from the single contributions of famous researchers and scientists in the 150 years spanning 1776 and 1925. This increasing level of electrochemical knowledge over the 19th century dovetailed with the industrial revolution, turning the electrochemical discoveries of Galvani, Volta, Faraday, Coulomb, and Ohm into familiar principles, infusing their initial discoveries into every aspect of modern science – it is fair to say that no present-day scientist operates a computer or instrument without electrical current. Although modern electrochemists are no longer household names, electrochemistry has indisputably had bridging function in science and industrial applications and is at the basis of all modern sciences, from materials sciences and theoretical chemistry to biochemistry and medicine. A broad swath of electrochemical research still has a rich impact on the world, and the major scientific awards in electrochemistry are now awarded for work in biology/medicine and energy. Galvani would certainly be surprised at the follow on impact of his early studies of frog legs, and where those results leaped to over the last 220 years. This chapter surveys the history from its beginnings.
Cornelia Breitkopf, Karen Swider-Lyons

2. Modern Electrochemistry

Abstract
An overview is given for the factors governing electrochemical reactions and processes: thermodynamics, kinetics, mass transport, ionic and electronic resistance, the charged electrode interface/double layer and the experimentation required to decouple these competing factors. These parameters are discussed in terms of the 28 chapters in the Springer Handbook of Electrochemical Energy. Important electrochemical references and resources are provided.
Cornelia Breitkopf, Karen Swider-Lyons

Thermodynamics

Frontmatter

3. Thermodynamical Aspects of Electrochemical Reactions

Abstract
The beginning of the transition from fossil fuels to renewable resources is associated with a change in energy conversion technologies and with a growing importance of electricity (Sect. 3.2). The application of electrochemical processes for the use and generation of electricity attains a new position in the energy conversion chain. Electrochemical reactions are associated with heat and electric power (work) exchange and are therefore thermodynamically complicated processes. Chemical and technical thermodynamics are important instruments for the understanding, classification and development of efficient electrochemical reactors and systems. As will be explained in this chapter, the analysis of electrochemical reactions on the basis of the Gibbs–Helmholtz equation allows for the definition of an equivalent temperature, which characterizes the energetic quality of the reaction under equilibrium conditions. The equivalent temperature is the ratio of the molar basic reaction enthalpy and the molar basic reaction entropy. The application of the exergy concept permits the determination of the irreversibilities and of the energetic quality of the exchanged heat as well as of all reaction educts and products (Sect. 3.2). Electrochemical reactions are associated with energy exchange at least at three temperature levels: heat at reaction temperature, work with a normalized exergy of unity, and the chemical conversion itself at its equivalent temperature. Hence, electrochemical reactions can be energy transformations in the sense of thermodynamical cycles, which is of high technological relevance. In addition, each educt and product represents a temperature level or, more precisely, its own normalized exergy. Thus, it is also possible to regard energy transformation processes at the level of substances. Open and closed electrochemical cycles will be considered, evaluated on the basis of their thermodynamical characteristics and compared with conventional processes.
Dietrich Hebecker

4. Thermodynamics of Electrochemical Systems

Abstract
The aim of this chapter is to show how a new extension of classical nonequilibrium thermodynamics, able to describe heterogeneous systems, can be applied in electrochemistry [4.1]. The aim is also to discuss how a further extension to mesoscopic systems can be used to describe nonlinear regimes, that is, the electrode overpotential. Electrochemical systems are heterogeneous, for instance, because the charge carrier changes across the system. We need to deal with charge transfer through a series of layers; the electrode, the electrolyte material layers, and interfaces between them. The extension of nonequilibrium thermodynamics to heterogeneous systems [4.1] enables us to deal with the variation in chemical potential and temperature across such layers in a systematic manner. We review the method that enables us to integrate across the layers, and explain coupled transfer of heat, mass and charge in such systems. The idea of mesoscopic nonequilibrium thermodynamics is next presented, and perspectives and new possibilities are pointed out.
Signe Kjelstrup, Dick Bedeaux

5. Multiscale Modeling of Solvation

Abstract
Statistical-mechanical, reference interaction site model (RISM) molecular theory of solvation is promising as an essential part of multiscale methodology for chemical and biomolecular nanosystems in solution. Beginning with a force field of site interaction potentials between solution species, it uses a diagrammatic analysis of the solvation free energy to construct integral equations for 3-D spatial correlation functions of molecular interaction sites in the statistical–mechanical ensemble. With the solvation structure so obtained at the level of molecular simulation, 3D-RISM-KH further yields the solvation thermodynamics at once as a simple integral of the correlation functions which is obtained by performing thermodynamic integration analytically. The latter allows analytical differentiation of the free energy functional and thus self-consistent coupling in various multiscale approaches. 3D-RISM-KH has been coupled with the KS-DFT and CASSCF quantum chemistry methods in a self-consistent field description of electronic structure, geometry optimization, nanochemistry, and photochemistry in solution. The multiple time step molecular dynamics of biomolecules steered by effective solvation forces obtained from the 3D-RISM-KH theory, accelerated by the generalized solvation force extrapolation, and stabilized by the optimized isokinetic Nosé–Hoover chain (OIN) thermostat, enables gigantic outer time steps up to tens picoseconds to accurately calculate equilibrium properties.
Andriy Kovalenko

Electrodes and Electrode Processes

Frontmatter

6. Highly Ordered Macroporous Electrodes

Abstract
In recent years, the field of highly ordered macroporous thin films coated onto solid electrode surfaces has received increasing attention, on the one hand, due to interesting fundamental questions, and, on the other hand, because of a large variety of potential applications of such designer structures, ranging from electrocatalysis to biosensors and energy storage/conversion. This chapter describes the synthesis, the characterization, and the features of such organized layers, with a special emphasis on an increasingly sophisticated and rational design, which is possible when using colloidal crystal structures as templates. Some possible applications of such modified electrodes are also highlighted in the last section of the chapter, illustrating their beneficial effects in various domains, going eventually far beyond pure electrochemical aspects.
In this chapter, we present the elaboration of highly-ordered macroporous electrodes using colloidal crystal templating. A structure is considered as macroporous, when the pore size exceeds 50 nm; pores with 2–50 nm are considered as mesopores, whereas pores smaller than 2 nm are termed microporous. Several techniques allowing the self-assembly of microspheres into colloidal crystal templates will be discussed in Sect. 6.1.1. After giving an overview in Sect. 6.1.2 over existing methods to infiltrate colloidal templates, Sects. 6.1.3 and 6.1.4 will focus on the controlled electrodeposition of metals and conducting polymers (CPs) into colloidal templates, and the electrochemical characterization of the resulting macroporous electrodes. Section 6.2 illustrates an approach to fabricate macroporous electrodes with complex pore architectures, including gradient pore structures. Assembly of colloidal microspheres into complex colloidal crystal architectures in a layer-by-layer deposition process using the Langmuir–Blodgett technique followed by infiltration of the template by electrochemical deposition enabled us to obtain this objective. In Sect. 6.3, we focus on miniaturized macroporous gold electrodes with a cylindrical geometry and their utility with respect to the electrocatalytic reduction of oxygen. The broad field of applications, in which macroporous electrodes can be used for, is presented in Sect. 6.4.
Alexander Kuhn, Matthias Heim

7. Ion-Sensitive Electrodes

Abstract
In this chapter we introduce the basic methods of electroanalysis that utilize electrochemical reactions at the interface between the solution to be analyzed and different electrodes. Potentiometry, i. e., 7 equilibrium measurements with negligible current is discussed in detail, especially the newer developments of ion-selective electrodes. Experiments that involve charge transfer across the interface are discussed as well, to provide an overview of the most established electroanalytical methods and sensors, comprising constant potential, swept potential, and constant current in quiet solutions or with forced mass transfer.
Hans-Hermann Rüttinger

8. Transport in Liquid-Phase Electrochemical Devices

Abstract
Transport of reactants and products in liquid-fed electrochemical cells is critical in terms of reactant utilization, concentration polarizations, and coulombic efficiencies. Design of electrochemical flow cells can benefit from adequately detailed models that capture the locally variable impact of reactant depletion and product build-up on electrochemical reactions throughout the cell. This chapter illustrates the importance of transport modeling by presenting a finite-volume, two-dimensional (2-D) model of a liquid-phase electrochemical cell with simple cell geometry, but complex multistep chemistry at each electrode incorporating parasitic reactions and/or mixed potentials. The modeled cell involves two half-cell reactions, borohydride (\(\mathrm{BH_{4}^{-}}\)) oxidation and hydrogen peroxide (H2O2) reduction, in planar flow channels with electrodes separated by flowing liquid-phase electrolytes and an ion-exchange membrane. This generic cell topology is representative of many fuel cells and flow batteries. The finite-volume model solves for conservation of mass, momentum, species, and charge in both the cathode and anode flow channels for ideal, dilute, and concentrated electrolytes. The model couples the flows to complex boundary conditions at the electrochemically active electrode surfaces and the selective ion-exchange membrane. Model results show that the balance of advection, diffusion, and migration in the liquid electrolytes results in complex profiles that predict boundary layer build-up and significant advection perpendicular to the flow path. The direct borohydride-hydrogen peroxide fuel cell transport model, used to illustrate these concepts, shows how liquid-phase transport limits conversion and dictates cell voltages within the context of the competing reactions at the two electrodes. The chapter ends by demonstrating how such a model can be implemented in design studies to explore strategies for improving practical cell performance.
Richard O. Stroman, Greg Jackson

9. Catalyst Layer Modeling

Abstract
The overall performance of a fuel cell or an electrochemical reactor depends greatly on properties of catalyst layers, where electrochemical reactions take place. Optimization of these structures in the past was mainly guided by experimental methods. For substantial progress in this field, combination of experiments with modeling is highly desirable. In this chapter focus is on macroscale models, since at the moment they provide more straightforward relationship to experimentally measurable quantities. After introducing the physical structure of a catalyst layer, we discuss typical macroscale modeling approaches such as interface, porous, and agglomerate models. We show how governing equations for the state fields, like potential or concentration can be derived and which typical simplifications can be made. For derivations, a porous electrode model has been chosen as a reference case. We prove that the interface model is a simplification of a porous model, where all gradients can be neglected. Furthermore, we demonstrate that the agglomerate model is an extension of the porous model, where in addition to macroscale, additional length scale is considered. Finally some selected examples regarding different macroscale models have been shown. Interface model has low capability to describe the structure of the catalyst layer, but it can be utilized to resolve complex reaction mechanisms, providing reaction kinetic parameters for distributed models. It was shown that the agglomerate models, having more structural parameters of the catalyst layer, are more suitable for catalyst layer optimization than the porous models.
Tanja Vidaković-Koch, Richard Hanke-Rauschenbach, Isaí Gonzalez Martínez, Kai Sundmacher

10. Water Management in Proton Exchange Fuell Cells

Abstract
After providing the basic thermodynamic and electrochemical laws and relationships, this chapter investigates the impact of reactant humidification for a polymer electrolyte membrane based fuel cell system. As an example, an air humidifier model operated under coflow, counterflow, and crossflow conditions (independent of separator material) is described. The model includes the operation characteristics of a mass exchanger based on three dimensionless parameters: The dimensionless concentration change, the dimensionless transfer capacity (number of transfer units), and the ratio of the volume flow rates. In this model the whole humidification process (governed by humidifier design and separator material properties) is described based on a single characteristic value, the effective mass transfer coefficient. The model provides a deeper understanding and prediction capability of the transfer processes which is helpful for humidifier design, controlling humidifier operation conditions, and might even make sensors unnecessary.
Nils Brandau, Jürgen Köhler

11. Calculations in Li-Ion Battery Materials

Abstract
Density functional calculations, or first principles calculations, are emerging as a critical tool for the evaluation of new lithium-ion battery materials. Density functional theory (DFT) is ideal for battery materials because it can be used to calculate critical materials properties, such as electronic and ionic conductivity, phase stability with lithium intercalation, and the roles of defects and dopants. The methods are illustrated herein by the evaluation of charge/discharge properties of two Li-ion battery cathode materials, \(\mathrm{LiNi}_{1/3}\mathrm{Co}_{1/3}\mathrm{Mn}_{1/3}\mathrm{O}_{2}\) (NCM) and \(\mathrm{LiNi}_{1/3}\mathrm{Co}_{1/3}\mathrm{Al}_{1/3}\mathrm{O}_{2}\) (NCA\({}_{1/3}\)) and their comparison to a LiCoO2 standard. We investigate the effect of substituting Al for Mn on the structural and electronic properties of the compounds at various levels of Li deintercalation and correlate these to performance properties observed in the laboratory. We find a calculated and observable upward shift in the voltage with Al substitution due to a shift in the oxidation levels of the electrochemically active ions during cycling. The results are corroborated by experimental results, in which we observe much lower specific capacity for NCA (despite its higher theoretical value) that can be attributed to a restricted voltage window during deintercalation. There is also a strong increase in resistive losses for NCA. A comparison of our density functional calculations and measured data indicates that this loss is due mainly to disruptive Ni/Li cation disorder. The partial density of states of the materials can be used to calculate their propensity to evolve O2 when overcharged. DFT gives key insights into changes occurring at the atomistic level and can be used toward physical insights into both new and traditional materials.
Michelle D. Johannes, Corey T. Love, Karen Swider-Lyons

Electrochemistry Probes

Frontmatter

12. Electrochemical Energy Generation and Storage as Seen by In-Situ NMR

Abstract
This chapter will provide a concise review/snap-shots of the development of in situ electrochemical nuclear magnetic resonance spectroscopy (including magnetic resonance imaging), in both solution and solid state, and its current state of applications to understanding chemical processes for electrochemical energy generation and storage. This will include pedagogical descriptions of involved principles and techniques and discussions of representative case studies that showcase the technical prowess of the methodologies, particularly in investigating nanomaterials used in electrocatalysis for fuel cells and energy storage devices (batteries) and associated water distribution in the former and Li metal deposits in the latter.
YuYe J. Tong

13. Spectroscopy of Electrochemical Systems

Abstract
The partnering of electrochemical and spectroscopic methods into a single experiment can yield unprecedented insights into the behavior of redox active materials and into interfacial processes. The application of coupled electrochemical and spectroscopic techniques, collectively called spectroelectrochemistry, has grown dramatically over the past three decades to the point that almost every spectroscopic technique available has been applied under potential control. Spectroelectrochemistry has found application across diverse fields from materials science, corrosion, and electronics to biochemistry and its progress has tracked the advances in microscopy and other optical methods providing increasingly detailed insights into electrochemical processes in diverse environments. This chapter describes the experimental considerations and application of spectroelectrochemistry as applied specifically to optical spectroscopy. We describe the experimental demands of applying electrochemical control to spectroscopic experiments across the most common optical formats. We examine specific applications of absorbance, emission, and vibrational spectroscopies under electrochemical control across a range of of materials, including inorganic, supramolecular structures, and polymers. Application of both steady-state and time-resolved spectroscopies to spectroelectrochemistry are examined and finally we anticipate the growing application of spectroelectrochemistry to some of the most recent advances in optical methods, particularly super-resolution methods and single molecule methods.
James J. Walsh, Robert J. Forster, Tia E. Keyes

14. Kinetic Activity in Electrochemical Cells

Abstract
The oxygen reduction reaction (ORR) is typically the rate-limiting reaction in electrocatalytic energy systems wherein the oxidizer is air, such as proton exchange membrane fuel cells (PEMFCs) or metal–air batteries. The effectiveness of these air-breathing electrochemical technologies hinges on the use of highly active electrocatalysts that can convert O2 to H2O (four-electron reaction) rather than the undesirable product H2O2 (two-electron reaction). The evaluation of new electrocatalysts in full cells is not practical due to competing contributions of mass transport and \(I^{2}R\) losses in the electrodes to measurements of kinetic activity. This chapter describes characterization of the electrocatalyst kinetic activity in electrochemical cells by rotating disk electrode (RDE) and rotating ring disk electrode (RRDE) methodologies and describes specifically how to apply the methodology to the porous electrodes used in energy systems. When the experimental procedures are executed properly, RDE and RRDE methodologies can be used to determine electrocatalyst ORR activities as a screening tool prior to full cell testing. Detailed methods are given for the accurate determination of the ORR of two standard materials: platinum/carbon in acid for PEMFC cathode catalysts, and MnO2 in base for metal–air batteries.
Yannick Garsany, Karen Swider-Lyons

Energy Conversion and Storage

Frontmatter

15. Lithium-Ion Batteries and Materials

Abstract
Lithium-ion (Li-ion) batteries are now widely implemented as the power or energy source for everything from portable electronics to electric vehicles. The electrochemical charge storage in the batteries is intimately related to their material properties. This chapter gives an overview of the methods for characterizing battery materials, both ex situ and in situ in practical cells. An important consideration is the interphase between the active charge storage materials and the electrolyte, often called the secondary electrolyte interphase (SEI) layer. Different methodologies unlock different aspects of the battery materials and interphases. Standard test methods are summarized as well as emerging methodologies. Next generation Li-ion batteries, such as Li-sulfur and Li-air are also described.
Cynthia A. Lundgren, Kang Xu, T. Richard Jow, Jan Allen, Sheng S. Zhang

16. Materials for Electrochemical Capacitors

Abstract
The aim of this chapter is threefold. First of all, we will attempt to briefly highlight the differences between batteries and electrochemical capacitors (ECs), describe the general types of ECs (symmetric and asymmetric configurations), and present the electrochemical tools that are available to characterize these systems. Second, an EC is a complex device with many components (current collector, separator, active materials, external management electronics) and design features that ultimately determine the device characteristics. However, the advances in performance for future ECs that will be required for their broader implementation as an energy-storage technology will largely depend on new developments in electrode materials and electrolytes, which will be the focus of this chapter. Thus, this chapter will attempt to present a critical assessment of the materials that are currently being used and developed for hybrid ECs. Third, some current applications of ECs will be described in details and will clearly demonstrate that hybrid ECs are no longer a scientific curiosity and that they have found their place as energy-storage systems due to their unique characteristics. Finally, this chapter will be concluded by a section that presents the major role ECs will be playing in the field of energy storage and conservation.
Thierry Brousse, Daniel Bélanger, Kazumi Chiba, Minato Egashira, Frédéric Favier, Jeffrey Long, John R. Miller, Masayuki Morita, Katsuhiko Naoi, Patrice Simon, Wataru Sugimoto

17. Electrochemical Capacitors

Abstract
Having power and energy characteristics between batteries and conventional capacitors, electrochemical capacitors offer new opportunities in electrical engineering and a fertile ground for the development and refinement of new electrode materials. This chapter will begin by introducing the fundamentals of electrochemical double-layer capacitors and pseudocapacitors (Sect. 17.1). It will go on to describe the most commonly used methods (Sect. 17.2) for assessing the capacitance, energy, and power of electrochemical capacitors:
  • Constant current discharge (Sect. 17.2.1)
  • Cyclic voltammetry (Sect. 17.2.2)
  • Impedance spectroscopy (Sect. 17.2.3).
Electrode configurations and cell designs will be considered in Sect. 17.2.3, as well as practical concerns such as the electrolyte, the separator, and the current collectors, and common experimental pitfalls will be pointed out.
Colin G. Cameron

18. Kinetics of Fast Redox Systems for Energy Storage

Abstract
Flow batteries (also: redox batteries or redox flow batteries RFB) are introduced as systems for conversion and storage of electrical energy into chemical energy. Their position in the wide range of systems and processes for energy conversion and storage is outlined. Special attention in the discussion of current trends and developments is paid to enhanced electrocatalysis of the electrode processes inside these devices.
Rudolf Holze

19. Modern Fuel Cell Testing Laboratory

Abstract
Elements constituting a fuel cell laboratory are succinctly discussed using the experience developed at the Hawaii Sustainable Energy Research Facility. The information is expected to be useful to organizations with a desire to create or improve a fuel cell laboratory in view of the recent and anticipated fuel cell commercialization activities. Topics discussed cover a wide range with an emphasis on differentiating aspects from other types of laboratories including safety, fuel cell and test equipment, and methods used to characterize fuel cells. The use of hydrogen, oxygen and specifically introduced chemical species, and the presence of high voltages and electrical short risks constitute the most prominent hazards. Reactant purity, cleaning, test station control including data acquisition, and calibration are the most important considerations to ensure fuel cell characterization data quality. Cleanliness is also an important consideration for the fuel cell assembly and integration into the test station. The fuel cell assembly also needs to be verified for faults. Fuel cells need to be conditioned for optimum performance before a purposefully designed test plan is implemented. Many fuel cell diagnostic methods are available but novel techniques are still needed in many areas including through plane temperature distribution, stack diagnostics and mass transfer properties. The emphasis is given to commonly and sparingly used electrochemical techniques. In situ techniques include polarization, impedance spectroscopy, voltammetry and current distribution over the active area. Ex situ techniques include the rotating ring-disc electrode and the membrane conductivity cell. Other nonelectrochemical techniques are also useful to understand fuel cell behavior and include the analysis of reactant streams and condensed water, and spectroscopic measurements in combination with electrochemical cells (spectroelectrochemical cells).
Jean St-Pierre, Michael Angelo, Keith Bethune, Jack Huizingh, Tatyana Reshetenko, Mebs Virji, Yunfeng Zhai

20. Polymer Electrolyte Fuel Cells

Abstract
The practical application of theory to experiment and data analysis is a crucial component of effective advancement of electrochemical systems. This chapter takes the fundamental principles of fuel cell operation and the underlying scientific and engineering principles and applies them to laboratory experiments. Topics covered include experiments showing how fuel cell performance varies with test conditions, methodology to fit experimental data to a simple empirical model to extract physically meaningful parameters that govern fuel cell performance, impedance spectroscopy as a diagnostic for fuel cell performance, and data analyses methods to determine the performance of fuel cells. Methods are also given for the practical measurement of relevant items from cell assembly and cell pinch to relative humidity. While the lessons are relevant to all electrochemical systems, this chapter is primarily targeted at new entrants into this arena wishing to learn the basics of fuel cell operation and testing.
Vijay K. Ramani, Kevin Cooper, James M. Fenton, H. Russel Kunz

21. Next-Generation Electrocatalysts

Abstract
In this chapter, we provide a comprehensive review of the most recent advances in the field of efficient catalysts for oxygen reduction reaction (ORR) at fuel-cell cathodes, metal-inorganic nanocomposites. Extensive research has been focused on developing alternative metal-inorganic composites with phosphate compounds. A few examples of ORR catalysts in the aqueous solution will be introduced to help researchers more effectively select composite materials and understand the important reactions involved in fuel cells.
Seunghoon Nam, Chunjoong Kim, Yuhong Oh, Byungwoo Park

22. Methods in Biological Fuel Cells

Abstract
This chapter details the common analytical methods used to evaluate all types of biological fuel cells. These include in situ and ex situ techniques for studying the catalyst, the bioelectrodes, and the complete biological fuel cell. Spectroscopic methods include spectrophotometric kinetic assays, product analysis assays, and electrode characterization techniques. Electrochemical methods include methods for proving bioelectrocatalysis via voltammetry, studying biocatalyst kinetics via amperometry, and performing polarization and power curve measurements on complete biological fuel cells.
Shelley D. Minteer

23. Energy Conversion Based on Bio(electro)catalysts

Abstract
Redox enzymes can be efficiently coupled with an electrode surface giving prospect of highly efficient and selective bio(electrochemical) transformations for energy conversion and/or production of commodities or fine chemicals. One example is glucose oxidase that immobilized on the electrode surface and in the presence of glucose and oxygen reduction cathode generates electricity and D-glucono-1,5-lactone with applications in different industries. Other examples might comprise whole enzymatic cascades performing complex sequences of biochemical reactions, turning, for example, such inert and environmentally polluting substances (like CO2) into useful commodities (e. g., methanol). These processes have a significant potential for development of new enzyme-based production systems, with electrochemistry playing an important role, especially regarding electrochemical regeneration of redox enzymes (redox cofactors). Although the electrochemical regeneration is feasible, its efficiency is still too low to be considered competitive for industrial applications. In this contribution we consider some important aspects of electrochemical regeneration of enzymes and common co-factors. At first, working principles of two typical representatives of bioelectrochemical systems will be described, followed by a short discussion of so-called cell free systems and their relationship to bioelectrochemical systems. For practical development of bioelectrochemical systems, the thermodynamics of related processes as well as kinetics are important. We give some examples of enzymes showing reversible electrode behavior, as an inspiration. Mathematical modeling will play a significant role in the design and optimization of bioelectrochemical systems. For this reason, we show how nonlinear mathematical models for studying the kinetics ofenzymatic processes can be developed. Finally, we discuss some practical aspects of biotransformation with redox enzymes, including examples of electron transfer mechanisms, enzyme adaptation on process conditions, development of electrodes etc.
Tanja Vidaković-Koch

24. Photoelectrochemical Conversion Processes

Abstract
Society’s electrical needs are largely continuous. However, clouds and darkness dictate that photovoltaic solar cells have an intermittent output. A photoelectrochemical solar cell (PEC) can generate not only electrical but also electrochemical energy, and provide the basis for a system with an energy storage component. Sufficiently energetic insolation incident on semiconductors can drive electrochemical oxidation/reduction and generate chemical, electrical or electrochemical energy. Aspects include efficient dye sensitized or direct solar to electrical energy conversion, solar electrochemical synthesis (electrolysis), including water splitting to form hydrogen, environmental cleanup and solar energy storage cells. The PEC utilizes light to carry out an electrochemical reaction, converting light to both chemical and electrical energy. This fundamental difference of the photovoltaic (PV) solar cell’s solid/solid interface, and the PEC’s solid/liquid interface has several ramifications in cell function and application. Energetic constraints imposed by single bandgap semiconductors have limited the demonstrated values of photoelectrochemical solar to electrical energy conversion efficiency to 16 %, and multiple bandgap cells can lead to significantly higher conversion efficiencies.
Photoelectrochemical systems may facilitate not only solar to electrical energy conversion, but have also led to investigations in solar photoelectrochemical production of fuels and photoelectrochemical detoxification of pollutants, and efficient solar thermal electrochemical production (STEP) of metals, fuels, bleach and carbon capture [24.1].
Stuart Licht

Electrochemical Processes

25. Advanced Extractive Electrometallurgy

Abstract
This chapter starts with a brief introduction of current technologies for metal extraction via chemical and electrochemical means. A focus is given to recent research and development of new methods for titanium extraction. The chapter is then devoted to describing the principle and methodology of the more recently proposed Fray–Farthing–Chen (FFC) Cambridge process, which is a molten salt-assisted solid-state electrochemical reduction process. Typical examples are highlighted for application of the FFC Cambridge process for extraction of titanium, silicon and other metals, and also the production of various metal alloys, and the related development of fundamental understanding of the proposed in situ reduction routes from physical, chemical, and electrochemical points of view. The unique ability of the FFC Cambridge process for near-net-shape production of metallic components directly from their metal oxide precursors is also discussed.
Di Hu, George Z. Chen

26. Electrodeposition of Nanomaterials

Abstract
This chapter describes various processes for electrodeposition of nanomaterials including:
1.
Template-free direct electrodeposition of nanoparticles with unique shapes, nanowires, nanotubes, and conducting polymer nanostructures
 
2.
Fabrication of various templates for template-assisted electrodeposition, and electrodeposition of nanowires, -rods, -tubes using the templates
 
3.
Electrodeposition of nanoparticles, -wires, -wire arrays on highly oriented pyrolytic graphite (HOPG)
 
4.
Electrodeposition using lithographically patterned methods, such as photolithographic, interference lithographic, electron-beam lithography (EBL) methods, and electrochemical lithographic methods.
 
Finally, examples of using the electrodeposited nanomaterials for the lithium-ion batteries (LIBs), and pseudocapacitors are presented.
This chapter outlines the representative electrochemical strategies in the recent literature for the fabrication of nanostructured materials, such as metals, alloys, polymers, and semiconductors. In view of the fact, the electrodeposited nanomaterials have numerous applications; this chapter will focus on the applications of these nanomaterials for the energy storage and conversions.
I-Wen Sun, Jeng-Kuei Chang

27. Electrochemical Hydrogen Production

Abstract
The electrochemical–photoelectrochemical production of hydrogen has been widely investigated for decades, largely driven by the potential to reduce environmental impact, satisfy distributed demand, and enhance public perception. As an alternative to steam methane reforming for hydrogen production, these approaches have enjoyed renewed vigor over the last several years. This chapter reviews recent progress in low-temperature electrolysis, high-temperature electrolysis, and photoelectrochemical techniques. Perspectives are given on the electricity consumption, carbon dioxide emission, costs of hydrogen production, and competitive landscape in the future hydrogen market.
Ting He, Mahaprasad Kar, Neal D. McDaniel, Bruce B. Randolph

28. Electrochemical Machining

Abstract
Electrochemical machining (ECM) is an interesting and effective technique to shape metals by controlled anodic dissolution at extremely large current densities. The process avoids mechanical stress to workpiece and tool and yields shiny surfaces without further processes. The hardness of the material has no influence on the process. A compact overview with focus on the fundamental electrochemical interface kinetics is presented. After a brief introduction and a historical abstract, the electrochemical processes of anodic dissolution are discussed (Sect. 28.2). The common interface models developed over the last decades are introduced and compared. Experimental research concepts in lab-scale with partly unique equipment are described in Sect. 28.3 which focuses on the principles of interface process due to the extremely high current densities which are typical for ECM. Further information comes from in situ techniques to analyze the reaction products in the electrolyte and to monitor the anode surface. Extensively discussed is the formation of supersaturated product films close to the anode as a consequence of the high dissolution rate during the process. In Sect. 28.5 the authors propose a classification of the ECM processes based on the individual metal properties and structures of surface films (oxides) or the types of product complex ions. The interplay between anodic dissolution, metal microstructure and crystallography is intensively described in the second part of the chapter. Side reactions such as anodic oxygen evolution and the corresponding aspects of electronic conductivity are separately discussed in Sect. 28.7. Pulse ECM is an improved technique which means more complex kinetics of dissolution and is described in Sect. 28.8. The overview is completed by a discussion about difficult-to-machine materials such as titanium and carbides or nitrides (Sect. 28.9).
Michael Schneider, Manuel Lohrengel

Backmatter

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