Fundamentals and Applications of Organic Electrochemistry

Synthesis, Materials, Devices

Toshio Fuchigami, Mahito Atobe, Shinsuke Inagi

• Publisher: Wiley
• Year: 2014
• ISBN:
  9781118670736
• Edition: 1
• Topic: Physical Sciences
• Subtopic: Physical & Theoretical Chemistry

This textbook is an accessible overview of the broad field of organic electrochemistry, covering the fundamentals and applications of contemporary organic electrochemistry. The book begins with an introduction to the fundamental aspects of electrode electron transfer and methods for the electrochemical measurement of organic molecules. It then goes on to discuss organic electrosynthesis of molecules and macromolecules, including detailed experimental information for the electrochemical synthesis of organic compounds and conducting polymers. Later chapters highlight new methodology for organic electrochemical synthesis, for example electrolysis in ionic liquids, the application to organic electronic devices such as solar cells and LEDs, and examples of commercialized organic electrode processes. Appendices present useful supplementary information including experimental examples of organic electrosynthesis, and tables of physical data (redox potentials of various organic solvents and organic compounds and physical properties of various organic solvents).

1
Fundamental Principles of Organic Electrochemistry: Fundamental Aspects of Electrochemistry Dealing with Organic Molecules

Mahito Atobe

Chemists often encounter situations in which a reaction does not proceed at a convenient rate under the initially selected set of conditions. In chemistry, activation energy is defined as the minimum energy required to start a chemical reaction, and hence the activation energy must be put into a chemical system in order for a chemical reaction to occur. Catalysts are often used to reduce the activation energy but a high temperature is still required for the reaction to proceed at an appreciable rate. Electrochemical reactions, however, can generally be carried out under mild conditions (room temperature and ambient pressure).

In electrochemical reactions there is an additional experimental parameter, the electrode potential, involved in the manipulation of electrochemical reaction rates. Electron transfer rates can easily be varied over many orders of magnitude at a single temperature by proper control of the electrode potential. Indeed, electrode potential is so powerful a parameter for controlling the rates of electrochemical reactions that most reactions can be carried out at or near room temperature.

An understanding of the nature of the dependence of electron transfer rates on potential is important for understanding electrode processes and constitutes the central theme of this chapter. Because electron transfer at an electrode surface is necessarily a heterogeneous process, it will be necessary to examine briefly the structure of the electrode–solution interface and its effects on the course of an electrochemical reaction. It is not enough, however, to simply derive the relationship between electron transfer rate and electrode potential. This is because as a result of the dramatic changes in these rates with potential, it is generally found that at certain potentials electron transfer is so fast that the overall process is actually limited by the rate of mass transport of the substrate from the bulk solution to the electrode surface. There are different modes of mass transport, and they differ in efficiency, therefore it will be necessary to examine each of these influences.

1.1 Formation of Electrical Double Layer

When electrodes are polarized in an electrolyte solution, the charge held at the electrodes is important. In order to neutralize a charge imbalance across the electrode–solution interface, the rearrangement of charged species like ions in the solution near the electrode surface will occur within a few hundredths of a second, and finally result in strong interactions occurring between the ions in solution and the electrode surface. This gives rise to the electrical double layer, whose thickness is usually between 1 and 10 nm (Figure 1.1) [1]. There exists a potential gradient over the electrical double layer and the gradient is no longer confirmed to the bulk electrolyte solution. The potential difference between the electrode surface and the bulk solution illustrated in Figure 1.1 may amount to a volt or more, over the rather short distance of the thickness of the double layer, and hence this is an extremely steep gradient, in the order of 10⁶ V cm⁻¹ or greater, which is an electrical field of considerable intensity. This is the driving force for the electrochemical reaction at electrode interfaces, therefore when the polarization between anode and cathode is increased gradually, the potential gradient in the vicinity of the anode and cathode is also increased and consequently the most oxidizable and reducible species in the system are subject to an electron-transfer reaction at the anode and cathode, respectively. Because a charge imbalance in the vicinity of an electrode takes place after the electron-transfer reaction, ions are transferred to the electrode interface to neutralize the imbalance, and consequently the continued Faradic current is observed. Thus, the electrolyte in a solution plays a role in the formation of the electrical double layer and the neutralization of a charge imbalance after electrolysis.

Figure 1.1 Electrical double-layer model and potential distribution in the double layer

1.2 Electrode Potentials (Redox Potentials)

In all electrochemical experiments the reactions of interest occur at the surface of the working electrode therefore we are interested in controlling the potential drop across the interface between the surface of the working electrode and the solution. However, it is impossible to control or measure this interfacial potential without placing another electrode in the solution. Thus, two interfacial potentials must be considered, neither of which can be measured independently. Hence, one requirement for the counter electrode is that its interfacial potential remains constant so that any changes in the cell voltage produce identical changes in the working electrode interfacial potential. An electrode whose potential does not vary with the current is referred to as an ideal non-polarizable electrode, but there is no electrode that behaves in this way. Consequently, the interfacial potential of the counter electrode in the two-electrode system discussed above varies as the current is passed through the cell. This problem is overcome by using a three-electrode system in which the functions of the counter electrode are divided betwee...

Table of contents

• Cover
• Title Page
• Copyright
• About the Authors
• Preface
• Introduction
• Chapter 1: Fundamental Principles of Organic Electrochemistry: Fundamental Aspects of Electrochemistry Dealing with Organic Molecules
• Chapter 2: Method for Study of Organic Electrochemistry: Electrochemical Measurements of Organic Molecules
• Chapter 3: Methods for Organic Electrosynthesis
• Chapter 4: Organic Electrode Reactions
• Chapter 5: Organic Electrosynthesis
• Chapter 6: New Methodology of Organic Electrochemical Synthesis
• Chapter 7: Related Fields of Organic Electrochemistry
• Chapter 8: Examples of Commercialized Organic Electrode Processes
• Appendix A: Examples of Organic Electrosynthesis
• Appendix B: Tables of Physical Data
• Index
• End User License Agreement