Cell design and electrodes

ECL solvent-supporting electrolytes systems (modified from reference (149)) 

Solvent Supporting electrolyte Potential range (V vs. SCR, at Pt) Remarks 

Acetonitrile TBABF4 TBAP, TRAP, TBAPFg -1.8 to +2.8 Good stability for both radical anions and cations potential range strongly depends upon purification 

Benzonitrile TBABF4 -1.8 to +2.5 Similar to acetonitrile in terms of ion stabilities commercial spectro-grade solvent can be used without purification 

Af-Dimethylformamide TBAP -2.8 to +1.5 Good stability for radical anions poor for cations difficult to purify and tends to decompose or hydrolyze on standing 

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Electrochemical engineering - the development and characterization of novel cell designs and electrode structures simplification of traditional cell desighs. 

The commonly used pretreatment protocols for activating solid electrodes are reviewed in this chapter. Specifically, the pietreatment of carbon, metal, and semiconductor electrodes (thin conducting oxides) is discussed. Details of how the different electrode materials are produced, how the particular pretreatment works, and what effect it has on electron-transfer kinetics and voltammetric background current are given, since these factors determine the electroanalytical utility of an electrode. Issues associated with cell design and electrode placement (Chapter 2), solvent and electrolyte purity (Chapter 3), and uncompensated ohmic resistance (Chapter 1) are discussed elsewhere in this book. This... 

Table 13.3 lists the commonly used solvent-supporting electrolyte systems for ECL study. 13.4.2 Cell design and electrodes... 

Current efficiency depends on operating characteristics, eg, pH, temperature, and cell design, and is generally in the 90—98% range. The cell voltage is a function of electrode characteristics and electrolyte conductivity and can be expressed as... 

Fig. 7.186. Reactor cell (a) and electrode configuration (b) for NEMCA studies using the fuel-cell type design, G-P, gal-vanostat-potentiostat. (Reprinted with permission from C. G. Vayenas, S. Bebelis, I. V. Yentekakis and H. Glintz, Catalysis Today 11 303,1992.)...

A similar effect can be expected for the carbon conductive diluent used in cathode formulations for all commercial cells. In all cases, it is necessary to take into account the particular cell design and the electrical resistivity of the electrode-active mass, perpendicular to the current collector, to optimize cell performance [8], One cannot standardize on any one type of carbon for all battery environments. Fortunately, since carbon is a versatile material, one can find a unique form for each application. 

In the following, the state-of-the-art of the electroreductive dehalogenation processes for environmental applications is critically reviewed in terms of substrates, electrode materials, reaction media, process and cell design and performances. 

Li metal served as a reference electrode and a IM-LiClO propylene carbonate solution was used as an electrolyte. Purification of the chemicals used and cell design and assembly were as previously reported (2). 

The information found in Chapters 1-3 and the considerations presented here can be translated into practical solutions of the problems of electrolysis in many ways, some of which are discussed in the next sections. Although the emphasis in this chapter is on laboratory-scale electrolyses and in Chapter 31 on industrial-scale work, it is clear that many of the factors that enter into consideration of cell design and choice of electrode, for example, are common to both. 

Porous electrodes may be used to achieve a high space-time yield, as they possess a large internal surface. A consequence of using such electrodes is, however, that interior mass transfer and ohmic resistance effects may lead to a nonuniform potential distribution, which affects the selectivity of the reaction. The cell design and the adjustable parameters must thus be optimized for each reaction [64-67,120]. 

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