Carbon cathode reaction

The CF cathode reaction is beheved to be a heterogeneous process, initiated by the insertion of lithium ions between the CF planes. It is completed by the extmsion of LiF and the coUapse of the stmcture to carbon. 

The cathodic reaction is the reduction of iodine to form lithium iodide at the carbon collector sites as lithium ions diffuse to the reaction site. The anode reaction is lithium ion formation and diffusion through the thin lithium iodide electrolyte layer. If the anode is cormgated and coated with PVP prior to adding the cathode fluid, the impedance of the cell is lower and remains at a low level until late in the discharge. The cell eventually fails because of high resistance, even though the drain rate is low. 

If too large a current is drawn from a Ledanche cell, the ammonia forms a gaseous insulating layer around the carbon cathode. When this happens, the voltage drops sharply and then returns slowly to its normal value of 1.5 V. This problem can be avoided by using an alkaline dry cell, in which the paste between the electrodes contains KOH rather than NH4CL In this case the overall cell reaction is simply... 

Oxidation of thiophene with Fenton-like reagents produces 2-hydroxythiophene of which the 2(570 One isomer is the most stable (Eq. 1) <96JCR(S)242>. In contrast, methyltrioxorhenium (Vn) catalyzed hydrogen peroxide oxidation of thiophene and its derivatives forms first the sulfoxide and ultimately the sulfone derivatives <96107211>. Anodic oxidation of aminated dibenzothiophene produces stable radical cation salts <96BSF597>. Reduction of dihalothiophene at carbon cathodes produces the first example of an electrochemical halogen dance reaction (Eq. 2) <96JOC8074>. 

C19-0125. The first battery to find widespread commercial use was the carbon-zinc dry cell, in which the cathode reaction is 2 Mn02( ) + q)+2e -> ZnMn2 04( ) In a flashlight, one of these batteries... 

In batteries of this type, solntions of lithium salts in thionyl chloride, SOCI2, are nsed as the electrolyte. Exceptionally, this strongly oxidizing solvent also serves as the active material for the cathodic reaction. Thus, during discharge thionyl chloride is electrochemicaUy reduced at a cathode made of carbon materials ... 

The reaction of H2 and O2 produces H2O. When a carbon-containing fuel is involved in the anode reaction, CO2 is also produced. For MCFCs, CO2 is required in the cathode reaction to maintain an invariant carbonate concentration in the electrolyte. Because CO2 is produced at the anode and consumed at the cathode in MCFCs, and because the concentrations in the anode and cathode feed streams are not necessarily equal, the Nemst equation in Table 2-2 includes the CO2 partial pressure for both electrode reactions. 

The spent oxidant composition is calculated in a similar manner. We note that in the MCFC, both oxygen and carbon dioxide are consumed on the cathode (air) side. This can be seen from the cathode reaction listed below and the following table listing the fuel cell reaction quantities. 

Figure 18. Discharge mechanism of a Li—SOCij ceii. The cell can operate until the surface of the carbon cathode is fully covered by electronically insulating LiCI and S discharge products. The Li—SO2 cell is also a soluble cathode system with a cell construction similar to that of the Li—SOCI2 cell. It follows a similar discharge reaction where the reaction product is L1S204.

Radical intermediates are also trapped by intramolecular reaction with an alkene or alkyne bond. At a mercury cathode this process competes with formation of the dialkylmercury [51], At a reticulated vitreous carbon cathode, this intramolecular cyclization of radicals generated by reduction of iodo compounds is an important process. Reduction of l-iododec-5-yne 5 at vitreous carbon gives the cyclopentane... 

Tetraalkylammonium salts are frequently used as the inert electrolyte in electrochemical reactions. These salts are however reductively decomposed in dimethylformamide at potentials around -2.96 V vs. see. At a glassy carbon cathode, tetra-... 

The ordinary dry cell (Leclanche cell) is a primary cell that is used in flashlights. In this cell, oxidation occurs at a zinc anode, and reduction at an inert carbon +" cathode (graphite). The space between the cell is filled with a moist paste of Mn02, ZnCl2 and NH CI. The half-reaction at the anode is as follows ... 

The Leclanche cell, the inexpensive disposable flashlight-type cell, has been on the market for over 100 years, yet its chemistry is not completely understood. The cell consists of an outer zinc shell that acts as the anode (seen by the external circuit as the source of electrons and hence the negative terminal) and oxidizes away during operation of the cell, a carbon rod or disk that serves as the cathodic current collector (positive terminal), and a moist paste of manganese dioxide, ammonium chloride, and zinc chloride that fills the cell and acts as both the electrolyte and the source of the cathodic reaction (reduction of MnIV). Usually, graphite in the form of carbon black is added to the paste to increase the electrical conductivity. The basic reactions are... 

A significant problem in scaling up the Kolbe reaction is the long-term stability of the expensive platinum anodes. Therefore, many attempts have been made to find a a cheaper anode material. One example is the Sowjet work 226), which shows that special carbon anodes can be used. Thus, the loss of carbon in the dimethyl sebacate synthesis (yield 72.2 %) after 8,400 Ah/m2 is only 0.008 %. Monsanto121) has attempted to pair the sebacate synthesis with various cathode reactions. 

As a first example of the use of reaction mechanism graphs, consider the electrochemistry of molten carbonate fuel cell (MCFC) cathodes. These cathodes are typically nickel-oxide porous electrodes with pores partially filled with a molten carbonate electrolyte. Oxygen and carbon dioxide are fed into the cathode through the vacant portions of the pores. The overall cathodic reaction is 02 + 2C02 + 4e / 2C03=. This overall reaction can be achieved through a number of reaction mechanisms two such mechanisms are the peroxide mechanism and the superoxide-peroxide mechanism, and these are considered next. 

The electrode where oxidation occurs, the zinc electrode in Figure 1 and the carbon electrode in Figure 2, is called the anode, while the electrode where reduction occurs is called the cathode. Reactions (1) and (2) are known as half-reactions, whereas reactions (3) and (4) are called oxidation-reduction (redox) reactions. 

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