Author: admin
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Cyclic Voltammetry
Cyclic voltammetry (CV) is a useful analytical tool for electrochemical engineers. It is often the first test performed to characterize a new electrolyte or an electrode. You will need to be familiar with the basic experiment and the interpretation of the data in order to obtain quantitative information. We begin at a potential that is…
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Electrode Kinetics and Double-Layer Charging
Recall from Chapter 3 that the surface of the electrode is usually charged, and that the structure of the interface is described as a double layer. The charge associated with the double layer depends on the electrode potential, and current must flow to alter this charge as either more or less charge is stored at the interface…
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Step Change in Potential or Current for a Semi-Infinite Planar Electrode in a Stagnant Electrolyte
As shown in Figure 6.3, we consider a planar WE located at x = 0. The CE is located sufficiently far from the working electrode so that it has no effect on the results. The reference electrode is assumed to be positioned just outside of the double layer. As before, the potential of interest is the potential of the…
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Overview
There are a multitude of experiments that can be performed with the basic three-electrode setup described above. Through a series of examples, we will explore a few of the more common ones, highlighting the main information that is obtained from each and its advantages and disadvantages. The key features of the any experiment are (1)…
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Electrochemical Cells, Instrumentation, and Some Practical Issues
The basic electrochemical cell used for analysis of electrochemical systems consists of three electrodes: the working electrode (WE), the counter electrode (CE), and a reference electrode (RE). The three-electrode setup is shown in Figure 6.1. The working electrode is where the electrochemical reaction being studied occurs. Typically, the potential or current of the working electrode is…
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Electrodes with Flow
Fluid flow is sometimes used with porous electrodes in order to bring reactants and products in and out of these high-surface-area electrodes. A number of different flow configurations are possible. Two basic categories are the flow-through and flow-by configurations (Figure 5.14). In the flow-through arrangement, the fluid flow is parallel to the current flow, and the fluid flow actually…
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Three-Phase Electrodes
There are situations where a stable three-phase structure is required. For example, the cathode of a low-temperature fuel cell involves three phases (gas, liquid, solid) in intimate contact. Let’s examine the reduction of oxygen in acid: The protons are supplied from the electrolyte, electrons supplied from a solid phase, and oxygen is in the gas…
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The Gas–Liquid Interface in Porous Electrodes
There are many instances when both gas and liquid fill the void volume of a porous electrode. Here, we introduce important concepts to describe these two fluids contained in the pores. A key aspect of porous media relevant for our studies is capillarity or capillary action. The capillarity can be understood from the ability of…
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Current Distributions in Porous Electrodes
As noted in Chapter 4, a uniform current distribution is often desired. Generally, the calculation of the current distribution for porous electrodes is not amenable to analytical solutions. There are a few exceptions—most notably the one-dimensional treatment of a porous electrode in the absence of concentration gradients, which is described by the secondary current distribution. In…
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Impact of Porous Electrode on Transport
Clearly, the porous structure has an effect on transport through the media. The way to treat this influence is to define effective transport properties that can be related to the bulk transport properties discussed in Chapter 4. The need for the effective transport properties can be seen with the cartoon illustrated in Figure 5.4. There are two…