Chemistry
Quantitative Electrolysis
Quantitative electrolysis refers to the process of using electrical current to drive a chemical reaction at an electrode in order to measure the amount of substance involved. This technique is commonly used in analytical chemistry to determine the quantity of a specific substance in a sample. By measuring the amount of electricity required to drive the reaction, the quantity of the substance can be accurately determined.
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3 Key excerpts on "Quantitative Electrolysis"
eBook - PDFElectrochemical Methods
Fundamentals and Applications
- Allen J. Bard, Larry R. Faulkner(Authors)
- 2012(Publication Date)
- Wiley(Publisher)
Although these techniques frequently involve simpler instru- mentation than controlled-potential methods, they require either a special set of chemical conditions in the cell or specific detection methods to signal completion of the electrolysis and to ensure 100% current efficiency. For preparative electrolysis (or electrosynthesis), constant-current methods can sometimes be used, as long as measures are taken to ensure that the electrode potential does not move into a region where undesirable side reactions occur. The general considerations and models employed in electroanalytical bulk electroly- sis methods are also often applicable to large-scale and flow electrosynthesis, to galvanic cells, batteries, and fuel cells, and to electroplating. Bulk electrolysis methods are also classified according to purpose. For example, one form of analysis involves determination of the weight of a deposit on the electrode (elec- trogravimetry). In this case 100% current efficiency is not required, but the substance of interest must be deposited in a pure, known form. In coulometry, the total quantity of electricity required to carry out an exhaustive electrolysis is determined. The quantity of material or number of electrons involved in the electrode reaction can then be deter- mined by Faraday’s laws, if the reaction occurred with 100% current efficiency. For elec- troseparations, electrolysis is used to remove, selectively, constituents from the solution. Several related bulk electrolysis techniques should be mentioned. In thin-layer elec- trochemical methods (Section 11.7) large A/V ratios are attained by trapping only a very small volume of solution in a thin (20–100 mm) layer against the working electrode. The current level and time scale in these techniques are similar to those in voltammetric meth- ods. Flow electrolysis (Section 11.6), in which a solution is exhaustively electrolyzed as it flows through a cell, can also be classified as a bulk electrolysis method.
eBook - PDF- Dieter Landolt(Author)
- 2007(Publication Date)
- EPFL PRESS(Publisher)
For example, Experimental Study of Electrode Reactions 193 the relaxation time of charge transfer reactions at the electrode-electrolyte interface is often smaller than that of transport phenomena in the electrolyte. Table 5.7 gives an overview of the most commonly used electrochemical non- steady-state methods (in parentheses: alternative names). Typically, one imposes a variation in either the current or the potential at the working electrode and then records its response as a function of time or frequency. Table 5.7 Electrochemical non steady state methods. Imposed quantity Form of applied signal Measured quantity Method E step I = f(t) potential step method (potentiostatic transient method) I step E = f(t) current step method (galvanostatic transient method) E, dE/dt linear sweep I = f(E, dE/dt) potential sweep method (linear sweep voltammetry) E, dE/dt cyclic sweep I = f(E, dE/dt) cyclic voltammetry ∆E = |∆E| sin (ωt) sine wave Z = f(ω) impedance method (impedance spectroscopy) 5.2.2 Potential step method A potential step is applied to the electrode, and the variation in current is measured as a function of time. This method has proven particularly useful for the identification of transport processes in the electrolyte and for studying the growth of passive oxide films (Chapter 6). Here, we develop the principle of the potential step method for a particularly simple reaction, namely, the electrodeposition of a metal under conditions where the deposition rate is controlled by mass transport. M + M n+ n e → (5.71) Assuming that the charge transfer reaction at the interface is sufficiently rapid for a quasi-equilibrium state to exist, the electrode potential follows the Nernst equation. If, in addition, the activity of the ion M is equal to its concentration the following n+ relation holds for the potential: E E RT nF c = + 0 ln s (5.72) Here c indicates the concentration at the metal surface.
eBook - PDF- Krystyna Jackowska, Paweł Krysiński(Authors)
- 2020(Publication Date)
- De Gruyter(Publisher)
2 Selected electrochemical methods applied in analytical chemistry and material science Applied electrochemistry utilizes numerous methods in its efforts to improve pro-gressively our quality of life through the understanding of charge transfer phenom-ena. These efforts lead to the construction and design of new devices and systems that can be used in industry (e.g., electrical energy storage and supply, catalysis and corrosion), and also in more personalized applications, such as batteries for smart-phones, laptops, and solar panels. Electroanalytical techniques provide unique in-formation on mechanisms and systems that are currently involved in the necessary development of the above areas. Both the instrumentation and theoretical funda-mentals have been advanced such that nonspecialists can easily use them in search of further development in technology, industry, and everyday life. Below we lay a brief background of selected electrochemical methods, commonly used in material science for: – characterization of interfaces; – characterization of electrode processes, kinetics, mass transfer; – corrosion studies; – coatings and paints; – investigations of membrane transport phenomena; – electrocatalysis, adsorption, and electrosorption studies; – studies of cells, batteries, fuel cells, supercapacitors; – conductive polymers; – semiconductors; – photoelectrochemistry and others. 2.1 Transient methods Before we start discussing selected electrochemical methods in this chapter, we have to summarize briefly some basics of the design of electrochemical cell that is typically used for such studies, as well as the electrode response to the applied po-tential, E , or introduced charge, Q , in terms of the measured current, i . First of all, since we already discussed that at the electrolyte/solution interface the electrical double layer is formed, accumulating and separating ionic charges, it behaves as a condenser.
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