Counter electrodes electrosynthesis

Figure 3.3 Sonoelectrochemical cell used for electrosynthesis and voltammetric studies. 1, Sonic horn 2, transducer 3, to control unit of sonic horn 4, graphite counter electrode 5, argon inlet for degassing 6, Pyrex reservoir 7, platinum-disk macro- or microelectrode 8, copper cooling coil connected to the thermostatted water bath 9, titanium tip 10, platinum resistance thermocouple 11, SCE reference. (From Ref. 557, reproduced with permission.)...

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... 

Dimensionally Stable Anodes— These anodes are composed of a base metal such as titanium, coated with a precious metal oxide (e.g., ruthenium dioxide). Such anodes can be used instead of Pt or carbon for oxygen evolution counter electrodes in an organic electrosynthesis. They have also found some applications for organic oxidation reactions [61]. 

The electropolymerization of thiophene-derivatives was conducted in a glove box using a two-electrode setup equipped with a Cu-mesh as counter electrode. The electrolyte used was the ionic liquid [BMIM][TFSI], which was deoxygenated by bubbling with nitrogen for 40 min and dried overnight with molecular sieves prior to use, containing 0.2M of either 2,2 -bithiophene or 3-methylthiophene [40]. Electrosynthesis was conducted under potentiostatic conditions at 3.2-3.4 V and 3.6-3.7 V for bi- and methylthiophene, respectively. Thereafter, the films were successively rinsed in [EMIM][BF4] and DI water, dried, and freed from their templated by dissolution in pure diethyl ether or a 2 1 mixture of diethyl ether and hexane. 

A one-compartment electrochemical cell used for electrosynthesis and EIS measurements. A large area, Pt gauze counter electrode (2.5 x 3.0 cm, AESAR) and a saturated Ag/AgCl reference electrode were used. TBAHFP(Aldrich) was used without further purification and dried in vacuum at 100 C for ca. 24 h prior to use, 3-Methylthiophene (Aldrich) was distilled in an... 

Miniaturized combinatorial electrosynthesis has been achieved by using a computer-controlled instrument equipped with a well-containing microtiter plates (Fig. 3) [7]. An electrode btmdle consisting of a PTFE holder, a working electrode, a CV microdisk, a reference electrode, and a counter electrode is moved from well to well automatically. Libraries of iminoquinol ethers and triazolopyridinium ions are generated by under controlled potential conditions. Progress of the electrolyses can be monitored by microelectrode steady-state voltammetry. 

Electrosynthesis of the polythiopene was realized on an indium-tin-oxide (ITO) electrode (glass blade covered with an indium-doped tin-oxide film). Before conducting the experiment, each electrode was cleaned by ultrasonication for 10 min in different solvents (acetone, dichloromethane, ether). Electrochemical experiments were performed in a three-compartment cell. The working electrode was the ITO electrode, the counter electrode was a Pt wke, and the reference electrode was an aqueous-saturated calomel electrode (E°/SCE = E°/NHE — 0.2412 V) with a salt bridge containing the supporting electrode. The SCE electrode was checked against the ferrocene/ferricinium couple (E = -1-0.405 V/SCE) before and after each experiment. 

In liquid ECAFM applications, the AFM tip and sample surface comprise the working and counter electrodes of an electrochemical cell. Additionally, a reference electrode can be incorporated into the liquid cell allowing the instrument to effectively perform as a three-electrode electrochemical cell. The technique has expanded into several applications where electrosynthesis and electrodeposition reactions can take place simultaneously with imaging [54]. Electrical connections can be made between the tip and enzymes on a surface to measure electron transfer and conductivity [44,52,55]. In addition, the tip can be functionalized with electroactive biomolecules to perform redox reactions and measure the amperometric and voltammetric response in situ [56]. 

Bubble electrodes — Mercury electrodes constructed in such a way that an electrolyte solution is entering a mercury-filled vessel through one or many small orifices in the bottom (cf. Fig. 1). The solution bubbles grow and will finally ascend in the mercury. The counter and the reference electrode have to be situated in the tubing fed to the orifice. Bubble electrodes have been developed as flow-through detectors for HPLC and FIA [i-iii,vi], as electrodes to generate ESR-active species [iii-iv], for - tensammetry [vii], and for electrosynthesis [v]. The fact that they are mercury based impeded further developments of this electrode type. 

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