Fundamentals of electrochemistry

Electrochemistry is the study of reduction-oxidation reactions (called redox reactions) in which electrons are transferred from one reactant to another. A chemical species that loses electrons in a redox reaction is oxidized. A species that gains electrons is reduced. A species that oxidizes is also called a reducing agent because it causes the other species to be reduced likewise, an oxidizing agent is a species that is itself reduced in a reaction. An oxidation-reduction reaction requires that one reactant gain electrons (be reduced) from the reactant which is oxidized. We can write the reduction and the oxidation reactions separately, as half-reactions the sum of the half-reactions equals the net oxidation-reduction reaction. Examples of oxidation half-reactions include  

If the direction of an oxidation reaction is reversed, it becomes a reduction reaction that is, if Al accepts 3 electrons, it is reduced to Al(s). AU of the reduction reactions are oxidation reactions if they are written in the opposite direction. Many of these reactions are reversible in practice, as we shall see. 

A net oxidation-reduction reaction is the sum of the appropriate reduction and oxidation half-reactions. If necessary, the half-reactions must be multiplied by a factor so that no electrons appear in the net reaction. For example, the reaction between Cu(s), Cu, Ag(s), and Ag is  

We shall see why the reaction proceeds in this direction shortly. The net reaction is obtained from the half-reactions as follows  

Each mole of copper gives up 2 moles of electrons, while each mole of silver ion accepts only 1 mole of electrons. Therefore the entire reduction reaction must be multiplied by 2, so that there are no electrons in the net reaction after summing the half-reactions  

The most significant breakthrough of electrochemistry came with the introduction of modern electronic equipment controlled by a computer with suitable software. This allowed experiments under much more extreme conditions which opened new fields of research and applications  

The studies and developments described in this book focus on the latter application, which is the development of sensors, with the aim of generating information from textile wet processes by immersing the developed sensor in the process bath and measuring parameters such as temperature, pH and concentration of the active compound. With this information, it is possible to improve and optimise the envisaged processes. 

Electrochemical methods are useful for the determination of chemical parameters, such as the concentration of analytes, through measurement of electrical parameters (current, potential, resistance, impedance) of an electrochemical cell. In this chapter, the relationship between electrical and chemical parameters will be described qualitatively. In the following chapters, this general approach will be discussed in more detail and applied to specific problems. 

An electrochemical reaction can be defined as a chemical reaction involving charge transfer through an interface. The most commonly known form of charge transfer is the transfer of electrons over a solid electrode-liquid electrolyte interface. In the simplest form, electrons can be transferred from the electrode to a chemical substance in solution (reduction), or electrons that were released from the chemical substance by oxidation can be taken up by the electrode. This is generally given by Equation 1.1  

A basic electrochemical cell always consists of at least two electrodes, schematically shown in Fig. 1.1, where two metallic electrodes are immersed 

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Electrochemical systems are found in a number of industrial processes. In addition to the subsequent discussions of electrosynthesis, electrochemical techniques are used to measure transport and kinetic properties of systems (see Electroanalyticaltechniques) to provide energy (see Batteries Euel cells) and to produce materials (see Electroplating). Electrochemistry can also play a destmctive role (see Corrosion and corrosion control). The fundamentals necessary to analyze most electrochemical systems have been presented. More details of the fundamentals of electrochemistry are contained in the general references. 

Fundamentals of Electrochemistry, Second Edition, By V. S. Bagotsky Copyright 2006 John Wiley Sons, Inc. 

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