Electrolytic cell, defined

Work function, a quantity of great importance in surface science and catalysis, plays a key role in solid state electrochemistry and in electrochemical promotion. As will be shown in Chapter 7 the work function of the gas-exposed surface of an electrode in a solid electrolyte cell can be used to define an absolute potential scale in solid state electrochemistry. 

The design optimization of an electrolytic cell aims at a high throughput with a low energy consumption at the lowest feasible cost. The throughput of an electrochemical reactor is measured in terms of the space time yield, Yt, defined as the volumetric quantity of the metal produced per unit time per unit volume of the process reactor. This quantity is expressed as ... 

If current passes through an electrolytic cell, then the potential of each of the electrodes attains a value different from the equilibrium value that the electrode should have in the same system in the absence of current flow. This phenomenon is termed electrode polarization. When a single electrode reaction occurs at a given current density at the electrode, then the degree of polarization can be defined in terms of the over potential. The overpotential r) is equal to the electrode potential E under the given conditions minus the equilibrium electrode potential corresponding to the considered electrode reaction Ec ... 

The cathode is defined as the electrode at which reduction occurs, i.e., where electrons are consumed, regardless of whether the electrochemical cell is an electrolytic or voltaic cell. In both electrolytic and voltaic cells, the electrons flow through the wire from the anode, where electrons are produced, to the cathode, where electrons are consumed. In an electrolytic cell, the dc source forces the electrons to travel nonspontaneously through the wire. Thus, the electrons flow from the positive electrode (the anode) to the negative electrode (the cathode). However, in a voltaic cell, the electrons flow spontaneously, away from the negative electrode (the anode) and toward the positive electrode (the cathode). 

Define cell, half-cell, anode, cathode, electrolytic cell, and galvanic cell. 

Apparatuses called coulometers are used for the measurement of the quantity of electricity. These are in principle electrolytic cells in which a given electrochemical process is allowed to proceed under exactly defined conditions it must be ascertained that the process in question proceeds in one direction only thus guaranteeing 100 p. c. current efficiency of electrolysis. From the amounts of products obtained which must be suitably determined, the quantity of electricity which passed through the cell can be calculated by applying Faraday s law. 

In an aqueous solution the ionic movement can be referred to the water molecules, which are unaffected by the applied electric field. But in a simple molten salt it is difficult to define the transport number because both ions are expected to move under the influence of the applied electric field. However, for a simple molten salt one can define an external transport number which is measured relative to a porous plug placed between the anode and cathode compartments of an electrolytic cell. Therefore, the ionic movement is related to a hypothetical exterior reference point of the molten salt. 

A single electrode potential, if defined as the difference in electrostatic potential between the spaces just outside the metal and the solution, is definite, but it cannot be measured by merely connecting up the phases with wires, and adjusting a potentiometer, until no current flows for this connexion introduces more than one phase boundary. Practically all electrolytic cells consist of at least three phase boundaries and the terminals at which the electromotive force of the cell is measured are, finally, of the same metal. There may, of course, be any. greater number of phase boundaries. A simple type of cell consists of two metals, M and M, dipping into a solution 8 containing the ions of each metal. 

The usual techniques for measiudng pH are applicable to aqueous solutions only. The electrolytic cell normally used to measure pH, when standardized by appropriate buffer solutions, yields a value of pH which is not exactly the same as, but is very close to —log Oh+ as defined by other methods. (Bates, 1954 Tanford 1955a). There is no assurance that this will be true in other solvents. 

To define a unique solution, we must specify the corresponding boundary and initial conditions. Normally electrolyte solutions are in contact with or bounded by electrodes. An electrode in its simplest form is a metal immersed in an electrolyte solution so that it makes contact with it. For example, copper in a solution of cupric sulfate is an example of an electrode. A system consisting of two electrodes forms an electrochemical cell. If the cell generates an emf by chemical reactions at the electrodes, it is termed a galvanic cell, whereas if an emf is imposed across the electrodes it is an electrolytic cell (Fig. 6.1.1). If a current is generated by the imposed emf, the electrochemical or electrolytic process that occurs is known as electrolysis. Now whether or not a current flows, the electrolyte can be considered to be neutral except at the solution-electrode interface. There a thin layer, termed a Debye sheath or electric double layer, forms that is composed predominately of ions of charge opposite to that of the metal electrode. We shall examine this double layer in Section 6.4, but for our purposes here it may be neglected. 

The boundary condition on the concentration at the cation exchange membrane is defined by the condition i =0, which is the same condition that applied at the cathode in the electrolytic cell examined in the last section. For the present problem from Eq. (6.1.16),... 

An electrochemical cell can be defined as two conductors or electrodes, usually metallic, immersed in the same electrolyte solution, or in two different electrolyte solutions which are in electrical contact. Electrochemical cells are classed into two groups. A galvanic (sometimes, voltaic) cell is one in which electrochemical reactions occur spontaneously when the two electrodes are connected by a conductor. These cells are often employed to convert chemical energy into electrical energy. Many types are of commercial Importance, such as the lead-acid battery, flashlight batteries, and various fuel cells. An electrolytic cell is one in which chemical reactions are... 

A galvanic current is the same as a DC current, and the term is used in particular for therapeutic applications and in electrochemistry. Anode and cathode are not defined from voltage polarity, but current direction. A galvanic (electrolytic) cell produces (passes) DC. If it does not, it is a dielectric cell and only displacement AC passes. Even so, an in-phase current may pass the cell, but it is due to dielectric losses and not DC conductance. Thus in-phase components are not the same as DC components. 

The electrolytic cells consist of lucite cylinders which are threaded at one end for stainless steel caps which contact the stainless steel cathode plating surfaces. A beveled lucite disk fits between the cap and cylinder and defines the electrodeposition area. 

The CLWZ is defined in one standard [7] as the space envelope where operation or maintenance is normally performed on or in the vicinity of exposed energized surfaces of electrolytic cell lines or their attachments. It extends, by definition, close to 2.5 m (8 ft) above and below live surfaces of the cells or attachments and 1.1m (3.5 ft) horizontally from the envelope just defined. It is taken not to extend through walls, roofs, floors, partitions, or the like. 

Electrochemical equivalent n. In an electrolytic cell, the mass of a metal deposited with the passage of 1 C of electricity. In the SI system, the coulomb is defined as lAs. Goldberg DE (2003) Fundamentals of chemistry. McGraw-Hill Science/Engineering/Math, New York. 

The equilibrium potential of an electrochemical reaction is defined as the potential of an electrode (with respect to the potential of a normal hydrogen electrode) when immersed in an electrolytic cell containing the reactive species, but without current flow. When a current is applied, the electrode potential is shifted. In the case of an anodic reaction ... 

In an electrolysis experiment, we generally measure the current that passes through an electrolytic cell in a given period of time. The SI unit of current is the ampere (A) defined as the amount of current corresponding to 1 coulomb of charge per second. 

The choice of the electrolyte is one of the most important tasks in designing a cell for a battery. The electrolyte electronically separates the electrodes from reacting directly in a chemical reaction, it transports electrochemically active species to/from the electrodes, and it is responsible for the Ohmic resistance of the cell that determines Joule s heating and the loss in power and usable electrical energy. In several cell types, the electrolyte takes even its own part in the main electrochemical reactions of the cell. Then, the electrolyte is defined by the specific cell reaction. In other cases, only concentrations of the electrolyte components can be varied within a limited range. Even if the electrolyte does not take part in the main electrochemical reactions, it still has a strong impact on the performance of the cell. Its chemical and electrochemical properties including... 

Reactor performance can be measured by a number of parameters. For electrolytic cells two important parameters are current efficiency C.E. and space-time yield Ygj.. (Current efficiency or current yield has been defined in Section 1.4.2.)... 

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