Chemistry
Electrochemical Cell
An electrochemical cell is a device that converts chemical energy into electrical energy through redox reactions. It consists of two electrodes (anode and cathode) immersed in an electrolyte solution. The flow of electrons between the electrodes generates an electric current. Electrochemical cells are used in batteries, fuel cells, and other energy storage and conversion devices.
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11 Key excerpts on "Electrochemical Cell"
eBook - PDFBatteries for Electric Vehicles
Materials and Electrochemistry
- Helena Berg(Author)
- 2015(Publication Date)
- Cambridge University Press(Publisher)
I Electrochemistry and battery technologies 1 The Electrochemical Cell The most fundamental unit of a battery is the Electrochemical Cell. All performance characteristics are dependent on the materials inside the cell, and all cells work according to some general principles independent of the materials employed. The purpose of this chapter is to bring together the fundamental aspects of an Electrochemical Cell as the basis for all further steps in the development of a battery intended for electric vehicles. An Electrochemical Cell converts chemical energy to electric energy when discharged, and vice versa. In addition, the Electrochemical Cells can be said to be either electrolytic or galvanic. In an electrolytic cell, the electric energy is converted to chemical energy (charging of the battery) and in a galvanic cell chemical energy is converted to electric energy (discharging of the battery). The basic design of an Electrochemical Cell consists of a positive and a negative electrode separated by an electrolyte, as shown in Figure 1.1. The chemical reactions taking place during charge and discharge processes are based on electrochemical oxidation and reduction reactions, known as the redox reactions, at the two electrodes. In these reactions, electrons are transferred via an external circuit from one electrode to another, and at the same time ions are transferred inside the cell, through the electrolyte, to maintain the charge balance. The species oxidised is called the oxidant, and the species reduced is called the reductant. The oxidation reaction takes place at the negative electrode, the anode, and electrons are transferred, via the external circuit, to the positive electrode, the cathode, where the reduction reaction takes place by accepting the electrons. The negative electrode is thus an electron donor, and the positive electrode an electron acceptor. During charge and discharge of a battery, the nomenclature of the electrodes changes.
eBook - PDF- Thomas F. Fuller, John N. Harb(Authors)
- 2018(Publication Date)
- Wiley(Publisher)
Hence, this chapter will introduce you to the key vocabu- lary of the discipline, as well as to some of the central aspects of electrochemical systems. In order to do this, we begin by looking at an Electrochemical Cell. 1.1 Electrochemical CellS Electrochemical Cells, such as the cell illustrated in Figure 1.1, lie at the heart of electrochemical systems. A typical Electrochemical Cell consists of two electrodes: an anode where oxidation occurs and a cathode where reduction takes place. Electrons move through an external circuit via an electronic conductor that connects the anode and cathode. The liquid solution that is between the two electrodes is the electrolyte. The electrolyte does not conduct electrons and does not contain any free electrons. It does, however, contain a mixture of negatively charged ions (anions) and positively charged ions (cations). These ions are free to move, which allows them to carry current in the electrolyte. The reactions take place at the electrode surface and are called heterogeneous electron-transfer reactions. For example, the electrodeposition of copper in the cell shown in Figure 1.1 can be written as Cu 2 + aq + 2e Cu s (1.1) Copper ions in solution accept two electrons from the metal and form solid copper. The reaction is described as heterogeneous because it takes place at the electrode surface rather than in the bulk solution; remember, there are no free electrons in the solution. Importantly, then, we see that electrochemical reactions are surface reactions. The metal that accepts or supplies electrons is the elec- trode. As written, copper ions gain electrons and therefore are reduced to form copper metal. When reduction occurs, the electrode is called the cathode. In the same cell, the reaction that takes place on the other electrode is Zn s Zn 2 + aq + 2e (1.2) The zinc metal is oxidized, giving up two electrons and forming zinc ions in solution. When oxidation occurs at the surface, the electrode is called the anode.
eBook - PDF- Arther Adamson(Author)
- 2012(Publication Date)
- Academic Press(Publisher)
CHAPTER THIRTEEN Electrochemical CellS The preceding chapter dealt primarily with the physical chemistry of electrolyte solutions; we now concern ourselves with the overall chemical process that occurs when electricity is passed through a conducting solution. The emphasis will be on the work associated with this overall change, as measured by the reversible cell potential. Since reversible work at constant temperature and pressure corre-sponds to a free energy change, we will thus be able to bring the emf of cells into the general scheme of thermodynamics. The chapter concludes with a discussion of irreversible electrode processes, that is, with the physical chemistry of the approach of ions to, and their reaction at, the surface of an electrode. 13-1 Definitions and Fundamental Relationships A. Cell Conventions An Electrochemical Cell has, as essential features, a current-carrying solution and two electrodes at which oxidation and reduction processes occur, respectively, as current flows. Figure 13-1 gives a schematic example of a fairly typical cell for this chapter; we have hydrogen and silver-silver chloride electrodes dipping into an aqueous solution of HCl. The hydrogen electrode, incidentally, typically consists of a platinized platinum metal surface arranged so that hydrogen gas bubbles past as it dips partly into the solution, the object being to provide the most intimate possible gas-solution-metal contact. Platinized platinum is merely platinum metal on which additional, very finely divided platinum has been deposited electrolytically; the result is a high area, catalytically active surface. A silver-silver chloride electrode consists of silver on which a fine-grained, adherent deposit of silver chloride has been placed, again electrolytically.
eBook - PDF- Arthur Adamson(Author)
- 2012(Publication Date)
- Academic Press(Publisher)
CHAPTER THIRTEEN Electrochemical CellS The preceding chapter dealt primarily with the physical chemistry of electrolyte solutions; we now concern ourselves with the overall chemical process that occurs when electricity is passed through a conducting solution. The emphasis will be on the work associated with this overall change, as measured by the reversible cell potential. Since reversible work at constant temperature and pressure corre-sponds to a free energy change, we will thus be able to bring the emf of cells into the general scheme of thermodynamics. The chapter concludes with a discussion of irreversible electrode processes, that is, with the physical chemistry of the approach of ions to, and their reaction àt, the surface of an electrode. 13-1 Definitions and Fundamental Relationships A. Cell Conventions An Electrochemical Cell has, as essential features, a current-carrying solution and two electrodes at which oxidation and reduction processes occur, respectively, as current flows. Figure 13-1 gives a schematic example of a fairly typical cell for this chapter; we have hydrogen and silver-silver chloride electrodes dipping into an aqueous solution of HCl. The hydrogen electrode, incidentally, typically consists of a platinized platinum metal surface arranged so that hydrogen gas bubbles past as it dips partly into the solution, the object being to provide the most intimate possible gas-solution-metal contact. Platinized platinum is merely platinum metal on which additional, very finely divided platinum has been deposited electrolytically; the result is a high area, catalytically active surface. A silver-silver chloride electrode consists of silver on which a fine-grained, adherent deposit of silver chloride has been placed, again electrolytically.
eBook - PDFChemistry
Principles and Reactions
- William Masterton, Cecile Hurley(Authors)
- 2020(Publication Date)
- Cengage Learning EMEA(Publisher)
430 17 ▼ Electrochemistry Most “silver” tableware like the ones in the painting are not made of pure silver but rather are silver-plated using an electrolytic cell. If by fire, Of sooty coal th’ empiric Alchymist Can turn, or holds it possible to turn Metals of drossiest Ore to Perfect Gold. —JOHN MILTON Paradise Lost (Book V, Lines 439–442) E lectrochemistry is the study of the interconversion of electrical and chemical energy. This conversion takes place in an Electrochemical Cell that may be a(n) ■ ■ voltaic (galvanic) cell (Section 17-2), in which a spontaneous reaction generates electrical energy. ■ ■ electrolytic cell (Section 17-6), in which electrical energy is used to bring about a nonspontaneous reaction. All of the reactions considered in this chapter are of the oxidation-reduction type. You will recall from Chapter 4 that such a reaction can be split into two half-reactions. In one half-reaction, referred to as reduction, electrons are consumed; in the other, called oxidation, electrons are produced. There can be no net change in the number of electrons; the number of electrons consumed in reduction must be exactly equal to the number produced in the oxidation half-reaction. These two half-reactions combine to give a balanced redox reaction (Section 17-1). In an Electrochemical Cell, these two half-reactions occur at two different elec-trodes, which most often consist of metal plates or wires. Reduction occurs at the cathode; ▲ a typical half-reaction might be cathode: Cu 2 1 ( aq ) 1 2 e 2 9: Cu( s ) Oxidation takes place at the anode, ▲ where a species such as zinc metal produces electrons: anode: Zn( s ) 9: Zn 2 1 ( aq ) 1 2 e 2 It is always true that in an Electrochemical Cell, anions move to the anode; cations move to the cathode . One of the most important characteristics of a cell is its voltage, which is a mea-sure of reaction spontaneity. Cell voltages depend on the nature of the half-reactions Cathode 5 reduction; anode 5 oxi-dation.
eBook - PDF- Krystyna Jackowska, Paweł Krysiński(Authors)
- 2020(Publication Date)
- De Gruyter(Publisher)
8 Electrochemistry in energy conversion and storage 8.1 Batteries 8.1.1 Electrochemical Cell – fundamentals The simplest Electrochemical Cell contains two electronic conductors (electrodes, mostly metals) and ionic liquid conductor containing ionic species (electrolyte) be-tween them. The electronic conductor and its interface with electrolyte serve as the place where the electrochemical reactions occur. To prevent any unwanted reaction with electrolyte species, it is often necessary to apply diaphragm dividing the cell into two parts (half cells). In this case, the additional potential is formed, called the liquid junction potential , which can be limited by means of a salt bridge or binary electrode. The schemes of exemplary cells without (A) and with junction (B) are as follows: Ag Ag 2 O , KOH aq , HgO Hg , Zn ZnSO 4 , aq CuSO 4 , aq Cu ð A Þ Zn ZnSO 4 , aq a 1 ð Þ CuSO 4 , aq a 2 ð Þ Cu , Zn ZnCl 2 , aq a 1 ð Þ AgNO 3 , aq a 1 ð Þ Ag B ð Þ The other kind of Electrochemical Cells are the concentration cells, in which the two half cells differ only in the concentration of the same electroactive species taking part in electrochemical reaction: Ag j AgCl , HCl aq a 1 ð Þ , H 2 ð p 1 Þ Pt − Pt j j H 2 p 2 ð Þ , HCl aq a 2 ð Þ , AgCl j Ag A ð Þ Ag AgCl , HCl aq a 1 ð Þ HCl aq a 2 ð Þ , AgCl j Ag B ð Þ As the voltage of concentration cells is low, they are not used practically in energy production and will not be considered further. Note that a slash | represents a phase boundary, a double slash || represents the phase boundary whose potential is negligible as a result of application of separator between the two electrolytes, and coma separates two components in the same phase. The overall chemical reaction in an Electrochemical Cell is formed by two inde-pendent half-reactions taking part in half cells, each of them characterized by the interfacial potential difference Δ φ (Galvani potential, see Chapter 1).
eBook - PDF- Young, William Vining, Roberta Day, Beatrice Botch(Authors)
- 2017(Publication Date)
- Cengage Learning EMEA(Publisher)
AlbertSmirnov/iStockphoto.com 21 Electrochemistry Unit Outline 21.1 Oxidation–Reduction Reactions and Electrochemical Cells 21.2 Cell Potentials, Free Energy, and Equilibria 21.3 Electrolysis 21.4 Applications of Electrochemistry: Batteries and Corrosion In This Unit… Why aren’t there more electric cars? Why do we still use corded power tools instead of only using battery-powered tools? Why do the batteries in our portable electronic devices run down so quickly? The answer to all these questions lies in our ability to make good batteries. In this unit we explore the chemistry of batteries, where spontaneous reactions take place by the indirect transfer of electrons from one reactant to another. We will also investigate electrolysis, the process where we use external power supplies such as batteries to force nonspontaneous reactions to form products. Copyright 2018 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-300 Unit 21 Electrochemistry 666 21.1 Oxidation–Reduction Reactions and Electrochemical Cells 21.1a Overview of Oxidation–Reduction Reactions In Chemical Reactions and Solution Stoichiometry (Unit 9) we first encountered oxida-tion–reduction reactions in our study of chemical reactions. Electrochemistry is the area of chemistry that studies oxidation–reduction reactions, also called redox reactions, which involve electron transfer between two or more species. Recall that in a redox reaction, ● the species that loses electrons has been oxidized and is the reducing agent in the reaction, and ● the species that gains electrons has been reduced and is the oxidizing agent in the reaction. Oxidizing and reducing agents are identified in a chemical reaction by using the oxida-tion number (or oxidation state) of the species in the reaction. Recall that the oxidation number of an oxidized species increases during the reaction, whereas the oxidation num-ber of a reduced species decreases during the reaction.
eBook - PDF- G R Jones(Author)
- 2013(Publication Date)
- Newnes(Publisher)
On the other hand, electrochemical power sources, batteries and fuel cells store chemical energy, which can be instantly converted into d.c. electrical energy by the turn of a switch. Corrosion, an electrochemical process, wastes both energy and materials. Some of the positive applications are discussed below. Because of the need to conserve conventional sources of energy (coal, oil, gas and nuclear), much attention is being given nowadays to the development of what are generally referred to as 'renewable' sources of energy (solar, wind, wave and tidal and geothermal) but, while these may supply relat-ively low-level local needs they are unlikely to replace conven-tional forms in high-level supplies of electrical power. It is worth noting, however, that electrical energy is best stored electrochemically and used directly in electrochemical reactors. Thus, all the branches of electrochemical technology discussed below are likely to be developed much further. For a comprehensive discussion of electrochemical techno-logy and the theoretical background the reader is referred to the book Industrial Electrochemistry. 1 40.2 Cells and batteries The term 'battery' means an assembly of voltaic primary or secondary cells. Batteries of secondary cells are also known as storage batteries or accumulators. In both types the individual cells consist of a positive and a negative electrode, immersed in an ionically conducting fluid, called the electrolyte, and generally separated by a porous non-conducting diaphragm, called the separator. The electrodes, which must be elec-trically conducting, may consist of a single rod or plate, or a number of these welded or bolted together in parallel. In some cells (for example, the conventional primary 'dry' cell) the outer metal container may constitute one of the electrodes.
eBook - PDFChemistry
The Molecular Nature of Matter
- Neil D. Jespersen, Alison Hyslop(Authors)
- 2021(Publication Date)
- Wiley(Publisher)
19.7 Electrolytic Cells 971 FIGURE 19.16 Diagram of the internal parts of a photovoltaic cell. a. Glass protective covering, b. antireflective coating, c. electrode mesh, d. n-type semiconductor material, e. p-type semiconductor material, f. electrode. The thickness of this cell is approximately 0.3 mm, and the n-type semiconductor is approximately 0.002 mm thick. FIGURE 19.17 Acres of photovoltaic cells can produce large amounts of energy. Stocktrek Images/Getty Images a b c d e Sunlight f 19.7 Electrolytic Cells In our preceding discussions, we’ve examined how spontaneous redox reactions can be used to generate electrical energy. We now turn our attention to the opposite process, the use of electrical energy to force nonspontaneous redox reactions to occur. When electricity is passed through a molten (melted) ionic compound or through a solu- tion of an electrolyte, a chemical reaction occurs that we call electrolysis. A typical electroly- sis apparatus, called an electrolysis cell or electrolytic cell, is shown in Figure 19.18. This particular cell contains molten sodium chloride. (A substance undergoing electrolysis must be molten or in solution so its ions can move freely and conduction can occur.) Inertelectrodes— electrodes that won’t react with the molten NaCl or the electrolysis products—are dipped into the cell and then connected to a source of direct current (DC) electricity. The DC source serves as an “electron pump,” pulling electrons away from one electrode and pushing them through the external wiring onto the other electrode. The electrode from which electrons are removed becomes positively charged, while the other electrode becomes negatively charged. When electricity starts to flow, chemical changes begin to happen. At the positive electrode, oxidation occurs as electrons are pulled away from negatively charged chloride ions. Because of the nature of the chemical change, therefore, thepositiveelectrode becomestheanode.
eBook - PDF- Keith Oldham, Jan Myland(Authors)
- 2012(Publication Date)
- Academic Press(Publisher)
Tin-plated steel sheet resists corrosion very well, but does have a drawback. If the plating becomes scratched, a site for corrosion is exposed and, since the entire remaining surface is available to serve as the cathode of a corrosion cell, intense oxidation occurs at the damage site and the sheet will be perforated faster than would an unplated sheet. Corrosion inhibitors can provide protection: these are often organic substances that adsorb on the metal surface where they slow down either the anodic or the cathodic member of the corrosion reaction pair. Other inhibitors act by forming a layer of precipitate, such as the metal phosphate, on the surface. Electrochemical methods of diminishing corrosion fall into two classes: cathodic protection (see Section 6:5) and anodic protection (see Section 9:7). 3:9 Summary 105 3:9 Summary The simplest Electrochemical Cell consists of an ionic conductor, usually an aqueous electrolyte solution, sandwiched between two electronic conductors, usually metals. The junctions are electrodes at which electrochemical reactions may occur. Some external connection from one electronic conductor to the other is needed before an electrode reaction occurs. When energy is being delivered from the cell into an external load, the cell is functioning galvanically; batteries and fuel cells provide useful examples, while corrosion represents the unwanted effect of a galvanic cell. When energy is being consumed in the cell, it is behaving electrolytically; many chemicals are manufactured in this way. An open-circuit cell develops a voltage that reflects the thermodynamics of the electrode reactions. If 3:9:1 oO + ... c ±ne~ * rR + ... and qQ + ... c ±ne~ * pP + ...
eBook - PDFSolar Energy Conversion and Storage
Photochemical Modes
- Suresh C. Ameta, Rakshit Ameta, Suresh C. Ameta, Rakshit Ameta(Authors)
- 2015(Publication Date)
- CRC Press(Publisher)
29 4 PhotoElectrochemical Cells Dipti Soni, Priya Parsoya, Basant K. Menariya, Ritu Vyas, and Rakshit Ameta 4.1 INTRODUCTION Photoelectrochemical (PEC) cells are the most efficient cells for converting solar energy into a more useful form of energy. These devices are quite simple to construct, and often consist of a photoactive semiconductor electrode (either n- or p-type) and a metal counterelectrode. Both of these electrodes are immersed in a suitable redox electrolyte. The PEC cells use light to carry out a chemical reac-tion for converting light to chemical energy. They have a solid–liquid interface, whereas photovol-taic (PV) solar cells have a solid–solid interface. The commercial use of a PEC solar cell depends on its conversion efficiency and stability. Various efforts have been made to make PEC cells more efficient, such as electrolyte modification, surface modification of the semiconductors, photoetching of layered semiconductors, semiconductor septum– based PEC solar cells, and so on. The dream is to capture the energy that is freely available from sunlight and turn it into electric power. The PEC cells based on III–V semiconductor electrodes have achieved high solar power con-version efficiencies in regenerative cells and in photoelectrolytic production of hydrogen. Miller (1984) discussed the corrosion chemistry associated with charge transfer at these interfaces, the influence of film formation, and the consequences for both photoanodic and photocathodic cells. Single-bandgap semiconductors in PEC cells have lower values (up to 16%) of energy conversion than the multiple bandgap cells that have significantly higher conversion efficiencies (Licht, 2001; Licht et al. 1998b,c,d). Energy production by these PEC processes has also been reviewed by Memming (1978). Bhavani et al. (1986) studied the reactions and PECs from the standpoint of energy conversion efficiency and the possibility of energy storage.
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