Strong Alkaline Electrolytes

Based on statistics, it can be seen that alkaline electrolytes are the most widely used aqueous electrolytes in the reported literature [2]. Compared to the strong acid 

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Aqueous, alkaline fuel cells, as used by NASA for supplemental power in spacecraft, are intolerant to C02 in the oxidant. The strongly alkaline electrolyte acts as an efficient scrubber for any C02, even down to the ppm level, but the resultant carbonate alters the performance unacceptably. This behavior was recognized as early as the mid 1960 s as a way to control space cabin C02 levels and recover and recycle the chemically bound oxygen. While these devices had been built and operated at bench scale before 1970, the first comprehensive analysis of their electrochemistry was put forth in a series of papers in 1974 [27]. The system comprises a bipolar array of fuel cells through whose cathode chamber COz-containing air is passed. The electrolyte, aqueous Cs2C03, is immobilized in a thin (0.25 0.75 mm) membrane. The electrodes are nickel-based fuel cell electrodes, designed to be hydrophobic with PTFE. 

In this scheme the k values represent rate constants, which are generally potential dependent. It must be emphasized that the four-electron pathway does not imply the transfer of four electrons in a single step rather, it underscores the fact that all intermediate species, such as, but not restricted to peroxide, remain bound to the electrode surface yielding, upon further reduction, water as the sole product. Also depicted in Scheme 3.1 are mass transport processes (diff) responsible for the replenishment of 02 and removal of solution phase peroxide next to the interface, and the adsorption and desorption of the peroxide intermediate, for which the rate constants are labeled as ks and k6, respectively. Not shown, for simplicity, is the one-electron reduction of dioxygen to superoxide, a radical species that exhibits moderate lifetime in strongly alkaline electrolytes [15]. 

Alkaline fuel cell (AFC) was used for Apollo and Space Shuttle program. Alkaline fuel cell employs liquid alkaline, e.g., KOH, as an electrolyte so that fuel, as well as air or oxygen, should be free of CO2 because the strong alkaline electrolyte reacts with CO2 to form carbonates, which reduces the ionic conductivity. Electrodes, e.g., Ni, Ag, and metal oxides, are relatively inexpensive compared to that of other fuel cells. 

The mercury battery is used extensively in medicine and electronic industries and is more expensive than the common dry cell. Contained in a stainless steel cylinder, the mercury battery consists of a zinc anode (amalgamated with mercury) in contact with a strongly alkaline electrolyte containing zinc oxide and mercury(ll) oxide (Figure 19.8). The cell reactions are... 

To get a clearer picture about the electrolyte effect on the performance of ESs, some typical comparative studies concerning various electrolytes including strong acid, neutral, and strong alkaline electrolytes are reviewed. For EDLCs, the majority of... 

The disadvantage of using AFCs is that the strongly alkaline electrolytes adsorb even the smallest amount of CO2 which, in turn, eventually reduces the conductivity of the electrolyte. (A number of AFC companies have claimed that this effect is not irreversible as the electrolyte can be changed.) For effective operation, it is also necessary to purify the oxygen used in the cell, and together these purifications can be very costly. 

Benzohydrol has been obtained by reducing benzophenone with sodium amalgam,1 with metallic calcium and alcohol,2 with hydrogen in the presence of a catalyst,3 with zinc, aluminium or sodium in strongly alkaline solutions,4 with zinc dust and alcoholic potassium hydroxide solution,5 and electrolytically.6... 

The major oxidation reactions of acetylene black in an alkaline electrolyte (30 wt% KOH + 2 wt% LiOH) are strongly dependent on the potential (vs. Hg/HgO) and temperature [30] ... 

The surface structure has a strong influence on the corrosion rate of carbon in both acid and alkaline electrolytes. Studies by Kinoshita [33] clearly showed that the specific corrosion rate mAcm"2 of carbon black in 96 wt% H3P04 at 160 °C was affected by heat treatment. A similar trend in the corrosion rate in alkaline electrolyte was observed by Ross [30c], as shown in Fig. 4. It is evident that the corrosion rates of the nongraphitized carbons are higher than those of the corresponding graphitized carbons. Their study further indicated that some types of carbon blacks (e.g., semi... 

If copper is present in the boiler FW (normally as the cupric ammonia complex ion), boiler surfaces are directly attacked by electrolytic reduction. In strongly alkaline conditions the ferrous ion is present as ferrous hydroxide [Fe(OH)2] ... 

Glass will be the most applied material for small cells (see e.g. Fig. 8). It is insulating and resistant against most electrolytes, except strongly alkaline and fluoride-containing media, and it can be used up to high temperatures. An important advantage is the possibility to observe reactions directly, for example. 

An alternative to the Leclanche cell is the alkaline manganese cell, in which the electrolyte is a strongly alkaline paste and the anode and cathode reactions in their respective compartments are... 

Tetrapositive Pr4+ and Tb4+ are quite stable in strongly alkaline carbonate solutions. Thus electrolytic oxidation for three hours of 2-5.5 mol dm-3 aqueous M2CO3 (M = K or Cs), 1 mol dm-3 in KOH, containing CeCl3, PrCl3 or TbCl3 (0.1-0.01 mol dm-3) gave stable solutions of yellow Pr4+ (Amax = 283 nm), dark reddish-brown Tb4+ (Amax = 365 nm), and of... 

Reduction of 4-(65) gave aldehyde 42 in strong acid and carbinol 31 in acetate buffer.99 In alkaline electrolyte, 31 would be further reduced to the picoline (19) (Scheme 19). The IV-phenylamide gave a mixture of the carbinol... 

The apparently simple procedures of partial dehydrogenation of pyrrolidines and partial hydrogenation of pyrroles afford Zl1-pyr-rolines. However, the reaction is complex and is of little preparative value.97-98 A 1-Pyrrolines may be obtained by isomerization of A 3-pyrrolines.100 From the preparative point of view, partial hydrogenation of quaternary pyridine salts in strongly alkaline media to give 1-alkyl-id 2-piperideines is more important.101 Formation of heterocyclic enamines was observed in the reduction of i -methyl-pyrrolidone with lithium aluminum hydride,102 -alkylpiperidones with sodium in ethanol,103,104 and in the electrolytic reduction of N-methylglutarimide.106... 

Lauryl hydroxysultaine is completely hydrolytically stable, a fairly high foamer and tolerant of electrolyte. It is used as a detergent in both strongly acid and strongly alkaline cleaners where amido-functional surfactants would not have sufficient shelf life due to hydrolysis. 

The Ni/MH battery operates in a strongly oxidizing medium composed of a high concentration alkaline electrolyte. Because many chemical elements react to form hydrides in an alkaline electrolyte, it follows that if these elements are used as electrodes, they will oxidize and fail to store hydrogen reversibly. As already mentioned, the highest electrochemical capacity is observed only after 30 cycles and then the capacity remained constant for almost 100 cycles, as shown in Figure 4. This clearly indicates that degradation of the electrode material is very slow. 

This thin film prevents the access of CIO- ions to the cathode but allows the liberated hydrogen to escape into the atmosphere and, also, the hydroxyl ions to migrate from the cathode into the bulk of the electrolyte. Chromate can bo used only in a neutral or a slightly acid solution because the protecting film dissolves in strongly acid as well as in strongly alkaline solutions. 

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