Counter electrode reactions

A typical counter electrode reaction is the electrolysis of water. Here the cathodic evolution of hydrogen is coupled with the formation of base, the anodic development of oxygen produces acid additionally. Frequently, acid and base formation at both electrodes will be balanced. Otherwise, a buffer solution or a (continuous) base/acid addition, for example, by a pH-controlling system, can enable the application of an undivided cell. 

Metal Dissolution Processes/Counter Electrode Reactions... 

As outlined in previous chapters the counter electrode reactions occurring in ionic liquids will be significantly different from those in aqueous solutions. Given the increased ohmic resistance that will be encountered compared to aqueous solutions it will be preferable to use soluble anodes which will decrease the over-potential that needs to be applied between the electrodes. Soluble anodes will also minimize the breakdown of the ionic liquid itself and retain the bath composition in its original state. 

In Chapter 11.1 some aspects of counter electrode reactions and metal dissolution were discussed. An interesting aspect in ionic liquid electrochemistry is that some reactive metals are quite noble. Aluminum, for example, is easily... 

Additional parameters should be mentioned including ohmic drop, counter electrode reaction, removal of oxygen, integration of the current, and finally work-up of the solution. 

Where Na is number of moles of A transformed. The counter electrode reaction must be chosen carefully in undivided cells to prevent reaction with the target product. The use of a sacrificial counter electrode may be satisfactory. The ideal solution is a paired electrosynthesis, i.e., when both cathodic and anodic processes are of interest. In most electrolyses, oxygen, which is electroactive, is a poison and must be removed by bubbling an inert gas through the solution or by vacuum techniques. When the electrolysis is complete, the product must be recovered. Obviously, there is no problem when the product precipitates or electrocrystallizes. The work-up of the solution may be facilitated by an appropriate choice of the experimental conditions. In... 

Since oxidized species are generated at the anode and at the same time reduced species evolve from the cathode these are likely to react together if allowed to meet. This is not usually a problem in electroanalytical studies where the total charge passed during a measurement is low, but must be taken into account for preparative electrolysis where stoichiometric amounts of charge are passed over significant time periods. It may be that the counter electrode reaction is gas evolution, in which... 

A counter electrode reaction is needed in the organic electrochemical reactor. The reactant and product(s) of this reaction must not interfere with the primary organic electrode reaction. Hence, a membrane separator is often used to divide the anode and cathode compartments of the reactor the membrane adds to the cost of the reactor and usually increases its operating voltage. 

The counter-electrode reaction often interferes and for this reason this electrode is usually physically separated from the sample solution by using a diaphragm or frit to create a liquid junction. External... 

Figure 14.5 illustrates the component and overall polarization curves when iron is inunersed in acidic solutions with and without Cu " ". The anodic polarization curves in both solutions are almost the same (line A). The counter electrode reaction in pure solution is the hydrogen evolution reaction, whose polarization behavior is shown by line B. These curves cross each other at point P, which is the mixed potential m(H). The anodic and the cathodic overvoltages are jFe(H) and — 7h respectively. The current density corresponding to m(H) is the corrosion current for iron in acid solutions, Jcorr(H)-When iron is placed in a solution containing Cu + ions, copper deposits on the iron substrate at the expense of iron corrosion. Note that the reversible potential of the Fe/Fe + couple of —0.44 V is less noble than that of the reversible potential for Cu/Cu " ... 

The fact that both cathodic and anodic reactions occur in a single cell means that the influence of the counter electrode reaction(s) must be duly... 

Oxygen evolution is the counter electrode reaction in several electrolytic processes (e.g. metal extraction, chromium plating, several organic electrosyntheses) while oxygen reduction is the desired cathode reactions in fuel cells and metalair batteries, a potential cathode reaction in improved chlor-alkali cells and a component reaction in corrosion. 

An electrochromic device is basically a two-electrode cell as mentioned in the introduction (Figure 1). In the construction of a two-electrode cell with only a single electrochromic material, there may be a problem with degradation reactions of the electrolyte diat occur because of the absence of an effective counter-electrode reaction. This limits operating lifetimes through destruction of the electrolyte and a build-iqi of degra tion products in the cell. The use of a reversible electrochromic material as a counter electrode or secondary electrode helps to avoid this problem. The secondary electrode, in electrochromic terms. 

The availability of a non-interferring counter-electrode reaction. This can be a... 

Firstly, there is a preponderance of reactions in aqueous solutions (in sharp contrast to the journal literature) and several oxidations in methanol, while aprotic solvents only appear in a few reactions as mixtures with water. The major reason for this is associated with the stability of the electrolysis medium especially with respect to the counter-electrode reaction. The cxidation/reduc-tion of water leads only to Oj-f and Hj + OH" and the reduction of methanol to Hj and CHjO", Hence, these reactions may conveniently be used to maintain the pH of the electrolyte at a constant level while leading to no contamination of the system. In contrast, the oxidation/reduction of aprotic... 

The electrolyses are performed by appl3dng a ccaistant potential difference (from 3 to 10 V) between the electrodes, the ament variations during each run being monitored by an ammeter. The metal sheet is made either the cathode or the anode, depending on what electrode reaction promotes the polymerization in situ of the system under investigation the counter electrode reaction is in any case supported by water dfeclurge, the products of which do not rignificantty affect the in situ reactions. 

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