Electrolytic cell classification

The emf of the cell, contrary to that in the absence of a liquid junction, depends on the transference numbers. Such cells are usually identified as concentration cells with presence of transference, the second one in the electrolyte concentration cell classification list. This system, as has been seen, contains a liquid junction across which it is possible for direct transport of ions to occur. 

The classification of electrode film systems is proposed based on the above ideas, and main qualitative regularities of the electrolytic processes in the film systems of different kind are envisaged in Chap. 4. In particular, the mechanism of formation of cathode deposits is considered. It is shown that the deposition of metal-salt carrots or compact metal layers depends on the properties of the cathode film system (prevailing type and ratio of the electronic and ionic conductivity of the film). The nature of crisis phenomena at the electrodes is also analysed (anode effect in fluoride melts, complications at the electrolytic production of Al-Si alloys in industrial-scale electrolytic cells), the mechanisms are elaborated and the means to escape the crises situations are developed. 

Fuel cells are primarily classified into five categories (Table 11.1) according to the electrolyte material used. Since the choice of electrolyte material plays an important role in determining the operating temperature of the fuel cell, this parameter may be used interchangeably in fuel cell classification. Table 11.1 presents the different kinds of fuel cells, respective electrolytes used, and operating temperature range of the fuel cell. 

The photovoltaic effect is initiated by light absorption in the electrode material. This is practically important only with semiconductor electrodes, where the photogenerated, excited electrons or holes may, under certain conditions, react with electrolyte redox systems. The photoredox reaction at the illuminated semiconductor thus drives the complementary (dark) reaction at the counterelectrode, which again may (but need not) regenerate the reactant consumed at the photoelectrode. The regenerative mode of operation is, according to the IUPAC recommendation, denoted as photovoltaic cell and the second one as photoelectrolytic cell . Alternative classification and terms will be discussed below. 

Most fuel cells being developed consume either hydrogen or fuels that have been preprocessed into a suitable hydrogen-rich form. Some fuel cells can directly consume sufficiently reactive fuels such as methane, methanol, carbon monoxide, or ammonia, or can process such fuels internally. Different types of fuel cells are most appropriately characterized by the electrolyte that they use to transport the electric charge and by the temperature at which they operate. This classification is presented in Table 7.4. 

Polymer electrolytes intended for applications in lithium-based cells could be roughly divided into two major classifications (1) those based on neat high polymers, which serve as both solvent to dissolve lithium salts and mechanical matrix to support... 

The fuel cell electrode reactions are catalyzed by different materials in different temperature ranges. A classification of the fuel cells can be made on the basis of the electrolyte, which in turn determines the operating temperature and, with it, the catalysts to be applied in the electrodes. The electrode reactions that take place in the different types of fuel cells are summarized in Table 3, which also lists the electrolytes and operating temperatures [56]. 

Table 3.2 reports the classification of the different types of fuel cells with some technical characteristics [6]. In this table the different electrolytes are specified together with the type of ions exchanged through them, while the catalysts indicated are those used on both anode and cathode to accelerate the semi-reactions (not necessary for SOFC thanks to their high operative temperature). 

Electrochemical reactors are heterogeneous by their very nature. They always involve a solid electrode, a liquid electrolyte, and an evolving gas at an electrode. Electrodes come in many forms, from large-sized plates fixed in the cell to fluidizable shapes and sizes. Further, the total reaction system consists of a reaction (or a set of reactions) at one electrode and another reaction (or set of reactions) at the other electrode. The two reactions (or sets of reactions) are necessary to complete the electrical circuit. Thus, although these reactors can, in principle, be treated in the same manner as conventional catalytic reactors, detailed analysis of their behavior is considerably more complex. We adopt the same classification for these reactors as for conventional reactors, batch, plug-flow, mixed-flow (continuous stirred tank), and their extensions. 

This is also called the Solid Polymer Fuel Cell (SPFQ and the Direct Methanol Fuel Cell (DMFC) is included in this classification. These cells use a solid perfluorinated sulfonated polymer ion exchange membrane (e.g. DuPont Nafion) [65] in the form of a thin plastic film, which serves as the electrolyte in the PEM fuel cell operating at 50-100°C. 

The most common classification of fuel cells is by the type of electrolyte used as shown in Table 1 which summarizes the most commonly used fuel cell technologies and their applications. The operating temperature and useful life of a fuel cell dictate the physicochemical and thermomechanical properties of materials used in the cell components (i.e., electrodes, electrolyte, intercoimect, cm-rent collector, etc.)... 

Carbonate Fuel Cell), and SOFC (Solid Oxide Fuel Cell). An exception to this classification is the DMFC (Direct Methanol Fuel Cell) which is a fuel cell in which methanol is directly fed to the anode. The electrolyte of this cell is not determining for the class. Table 1.1 compares the different types of fuel cell systems [2, 5-8]. A schematic representation of a fuel cell with reactant and product, and ions flow directions for these types of fuel cells are shown in Figure 1.2 [6]. 

Fuel cells are electrochemical devices that convert chemical energy contained in fuel directly into electrical energy through electrochemical reactions. Fuel cells consist of an anode, where the fuel is oxidized, a cathode where the oxidant is reduced and an electrolyte which separates anode from cathode and conducts ions. The general classification of fuel cells is usually based on the type of electrolyte used, and their operation conditions are typically related to the characteristics of the electrolyte. More detailed discussion of fuel cells as stand-alone power sources can be found in the next chapter of this book. 

In parallel with the classification by electrolyte, some fuel cells are classified by the type of fuel used ... 

A more detailed classification can be given - on the basis of the type of electrolyte present in the cell (Table 3.3). 

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