Electrode graphite felt

If both electrodes have to be made of materials, that are available only as foils or sheets or are not machinable, or for example, for materials, such as graphite felt, a cell design like the one in Fig. 9 is not realizable. Inlet and outlet systems have to be integrated in the electrolyte compartments. The parallel-plate and frame design of a laboratory flow-trough cell in Fig. 10 consists of easy-to-produce parts, using the fixing method for PTFE tubes in Fig. 4. 

As a result, a highly enantioselective oxidation of (22) was achieved by using a TEMPO-modified graphite felt electrode in the presence of (—)-sparteine, where the enantiopurity of the remaining (22) was >99% and the current efficiency for (23) was >90% (Scheme 8) [51]. However, this selectivity has been questioned [52]. 

A variety of phenol couplings have been described. Those reported before 1991 have been reviewed [66]. 2-Naphthol (27) was oxidized to l,l -binaphthol (28) in high current efficiency on a graphite felt electrode coated with a thin poly(acrylic acid) layer immobilizing 4-amino-2,2, 6,6-tetramethylpiperidinyl-l-oxy (4-amino-TEMPO) (Scheme 10) [67]. 

For cases directly comparable to the cyclization originating from (27) above, the yields of the product were not as high. However, a related reaction used in the synthesis of an 11-substituted dibenzo[a,d]-cycloheptenimine derivative was very successful as shown in Scheme 11 (Eq. 2) [32]. In this reaction, a controlled potential electrolysis of (33) led to the formation of the tetracyclic (34) in an 85% isolated yield. The reaction was performed on a 1 g scale using an undivided cell, a graphite felt anode, a stainless steel cathode, a saturated calomel reference electrode, and a 1% NaBF4 in 70 30 THF/water electrolyte solution. The electrolysis was scaled up further with the use of a flow cell. In this experiment, 200 g of (33) were oxidized in order to afford a 75% isolated yield of (34). 

Redox" electrolysis-constant current (graphite felt electrodes)... 

Coupling A graphite felt electrode chemically modified with TEMPO led to the enantioselective electrocatalytic coupling of 2-naphthol, 2-methoxynaphth-alene and 10-hydroxyphenanthrene with high enantioselectivity (up to 98% ee) in the presence of (-)-sparteine as a chiral base [366]. 

Supported electrodes. The mixture of catalyst and charcoal is poured into the space between two mechanically rigid walls, with asbestos paper as support and a graphite felt or metal sheet as current collector. No binder is necessary. With such electrodes, both liquid and gaseous working materials can be studied. For the experiments with dissolved fuels described in Section 4.2, we used modified electrodes of this type 6 mg chelate was mixed with 6 mg soot and poured between two graphite felt discs. 

Graphite felt as electrode material [ELECTROCHEMICAL PROCESSING - ORGANIC] (Vol 9)... 

E. M. Belgsir and H. J. Schafer, Selective oxidation of carbohydrates on Nafion -TEMPO-modified graphite felt electrodes, Electrochem. Commun., 3 (2001) 32-35. 

Graphite felt electrode -> carbon electrode, subentry -> carbon felt electrode... 

CN)2C=C(CN)2 this addition also improves the electrode kinetics. Current collection is improved by adding -> graphite felt mats into the electrode volume. 

Kalu and Oloman [75] studied the simultaneous synthesis of alkaline hydrogen peroxide and sodium chlorate in a bench-scale flow-by single-cell electrochemical reactor. A schematic of the electrode conditions is shown in Fig. 18. Graphite felt was used as the cathode to synthesize peroxide from 0.5 -2.0 M NaOH chlorate was the product at a dimensionally stable anode (DSA). The anodic and cathodic reactions were as follows ... 

Osa and coworkers [405,466] developed a graphite felt electrode modified with 2,2,6,6-tetramethylpiperidin-l-yloxyl (TEMPO) and applied it to enantioselective, electro-catalytic oxidative coupling of naphthol, naphthyl ether, and phenanthrol in the presence of (—)-sparteine as a base. The enantioselectivity of the coupling products were as high as 98%. 

Recently, Osa and coworkers [502] have reported highly enantioselective electroca-talytic oxidation of racemic monoalcohols using a TEMPO-modified graphite felt electrode in the presence of (—)-sparteine. Optically almost pure i -isomeric alcohols remained unreacted. Highly enantioselective lactonization of racemic diols was also achieved by using the same TEMPO-modified electrode to give (S)-isometric lactones [503]. 

Brunauer-Emmet-Teller (BET) estimated surface areas [23], For example, from Figure 5.9, graphite felt electrodes show poor volume-normalized ORR current density compared to carbon nanofibers and multiwaUed carbon nanotube (MWCNT)-based electrodes. However, the results also reveal that CNTs and porous carbon tubes exhibit dramaticaUy lower ORR current densities when normalized to B ET surface area, while graphite felt electrodes perform better, perhaps indicative of agglomeration of the carbon tubes, preventing enzyme adsorption over the entire area. Further research on methods to permit dispersion of nano-tubes, while retaining electrical conductivity and adsorption of enzymes oriented for DET, is warranted. 

Figure 5.9 Cathode polarization plots for electrodes with laccase adsorbed to graphite felt (curves a), porous carbon tubes (curves b), SWCNTs (curves c), MWCNTs (curves d), and carbon nanofibers (curves e).

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