Electrolysis without supporting electrolytes

The electrolysis apparatus for the polymerization is illustrated in Figure 2, which is characterized by a single cell without a partition membrane between the electrodes. In poor solvents of poly(phenyleneoxide) s such as methanol and acetonitrile, the polymer was deposited on the electrode, i.e. passivation of the electrode occured. Dichlo-romethane, nitrobenzene, and hydroquinone dimethyl ether were selected as the solvents because both the polymer and a supporting electrolyte dissolved in them and they were relatively stable under electrolysis conditions. 

Nanotubes and onions were also prepared by electrolysis of acetylene at —40 C in liquid ammonia, without deliberately added supporting electrolyte [101]. This is the lowest temperature record for the production of nanotubes. In contrast to reaction 4.14, this carbonization was not aided by a catalyst. The mechanism started from dissociation of NH3 ... 

Various electrochemical organic reactions have been carried out using electrochemical microflow reactors. Sometimes, electrolysis can be conducted without intentionally added supporting electrolyte by virtue of the extremely short distance between the anode and the cathode. 

Applications in Other Electrolyzers. Apart from applications in hydrogen-oxygen fuel cells and water electrolyzers which operate without any supporting electrolyte, SPE electrolyzers are also used efficiently with electrolyte solutions, such as HC1 and Na2SCK+. Recently, LaConti, et al (34), have reported the application of the cell with Nafion as SPE for some important electrochemical processes, including electrolysis of water, HC1, Na2S0 +, and brine solution. 

Iodonium and sulfonium salts undergo irreversible one electron electrochemical or chemical reduction [51,52], Reduction of diaryliodonium salts in water exhibit two to four waves in the polarogram depending upon the concentration of iodonium salt, type of electrode, nature and concentration of the supporting electrolyte, and the maximum suppressor [51,53-56]. Reductive electrolysis of diphenyliodonium salts in water at mercury yields mixtures of diphenylmercury, iodobenzene, and benzene, depending upon the potential used during the electrolysis [51,53-55]. Reduction at platinum or glassy carbon electrodes occurs without appearance of the first wave (see below) [54,56,57]. The mechanism shown in Scheme 1 was proposed for aqueous electrolysis of diphenyliodonium salts [51a] ... 

Solid-Liquid Biphasic System for Electrolysis Without Intentionally Added Supporting Electrolyte... 

Tajima and co-workers have developed a novel environmentally friendly electrolytic system using solid-supported bases and protic organic solvents such as methanol [24], This method permits electrolysis without an intentionally added supporting electrolyte. Solid-supported bases are not oxidized at the electrode surface because electron transfer between two solids is, in principle, very difficult [25], Therefore, protons generated by the reaction of a solid-supported base and a protic solvent may serve as carriers of electronic charge. After the electrolysis, the solid-supported base can be easily separated by filtration and can be re-used. 

Electrochemical microflow systems have also attracted significant research interest from the viewpoint of electrolysis without an intentionally added supporting electrolyte, becausethe short distance between the electrodes andthehigh electrode surfaceto reactor volume ratio are advantageous for conductivity and reaction efficiency. 

The electrolyte consisting of solvent and supporting electrolyte must dissolve the substrate sufficiently, supply the necessary conductance and be stable towards reduction or oxidation. The stability of the electrolyte can be expressed by the decomposition potential (potential at which the current density for oxidation or reduction of the solvent reaches about 10 pA cm for analytical experiments or 10 mA cm , respectively, for preparative scale electrolysis). The decomposition potential quotes the potential within which the electrolyte can be used without decomposition (Table 1). 

The potentiostatic electrolysis at a platinum electrode at +1-0 V results in a polymer layer on the electrode surface. After an induction period the electrode surface layer gives an ESR signal with one line of 0.15 mT linewidth (Fig.lO). The linewidth is independent on the radical concentration and the type of the cation in the supporting electrolyte. If the polyaniline film is in contact with aniline in the abscence of an applied potential, the line intensity decrease with time indicating a further reaction of the polymer with the aniline. Under UV-irradiation the free spin can be renewed without reaching its initial intensity (Fig.lOb). 

Kolbe electrolysis of the acids n-CsFg COaH and 0 (CF2)3 CF CF2 C02H, respectively." Despite the low conductivity of trifluoroacetic acid, it is possible to conduct electrolyses in this medium without the aid of a supporting electrolyte, and use has been made of this in the development of an excellent method for the preparation of stable solutions of certain radical-cations for example, solutions of the pmple thianthrenium trifluoroacetate (isolable by evaporation of CFs COjH) can be obtained by constant-current electrolysis of thian-threne in trifluoroacetic acid. Electrolysis of hexamethylbenzene in trifluoroacetic acid results in nearly quantitative formation of the trifluoro-acetoxylation product MegCe-CHa O CO-CFg, presumably via two-electron oxidation of the solute to pentamethylbenzyl cation."... 

Oldham, K.B. (1997) Limiting currents for steady-state electrolysis of an equilibrium mixture, with and without supporting inert electrolyte. Analytical Chemistry, 69,446-453. 

Now. this is not usually a problem for producing polypyrrole and related polymers. since a typical film on the electrode weighs only some tens of milligrams, and an electrolyte containing, for example, 0.01 M pyrrole can support its formation without appreciable depletion of the monomer. Constant-current electrolysis is therefore often used for these polymers although it should be noted that the exact properties of the film can vary with preparation conditions, and with this methodology the exact electrode potenhal is not known. 

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