Anodes electrically conducting oxides

Anodic corrosion of the niobium basket that supports the fuel is inhibited by an electrically conducting oxide film, which forms on the niobium. 

When a similar cell is made of iron electrodes instead of platinum, an adherent, electrically conducting oxide of iron forms at cathodic areas when in contact with aerated solution, this oxide acts as an oxygen electrode. But at anodic areas, Fe + forms, and the electrode acts as an iron electrode (( )° = -0.440 V). The operating emf of such a cell is much larger than that of the cell made up of platinum electrodes, with the value being given by... 

The major problem with direct electrocatalytic oxidation of the hydrocarbon fuel at the anode is the marked tendency towards carbon deposition via hydrocarbon decomposition (Eqs. (1) and (2)). It is extremely difficult to avoid carbon deposition in the absence of a co-fed oxidant. However, some recent studies have reported anodes which show considerable promise for the direct electrocatalytic oxidation of hydrocarbons [29,68,69]. The conditions under which these anodes can be used may present problems for their widespread application, whilst their long-term durability with respect to carbon deposition must be established. Electrically conducting oxides have also been proposed in recent years as having potential for use as anodes for the direct electrocatalytic oxidation of hydrocarbons [67.70,74]. 

Electrically conducting oxide materials have been investigated as potential anode materials. One of the main attractions of such materials is their resistance to carbon deposition compared to nickel cermet anodes under direct reforming conditions [67,70,74,79,80]. Rhodium, platinum and ruthenium have also... 

Fluorine is produced by the electrolysis of anhydrous potassium biduoride [7789-29-9] KHF2 or KF HF, which contains various concentrations of free HF. The duoride ion is oxidized at the anode to Hberate duorine gas, and the hydrogen ion is reduced at the cathode to Hberate hydrogen. Anhydrous HF caimot be used alone because of its low electrical conductivity (see Electrochemical processing, inorganic). 

Further improvements in anode performance have been achieved through the inclusion of certain metal salts in the electrolyte, and more recently by dkect incorporation into the anode (92,96,97). Good anode performance has been shown to depend on the formation of carbon—fluorine intercalation compounds at the electrode surface (98). These intercalation compounds resist further oxidation by fluorine to form (CF ), have good electrical conductivity, and are wet by the electrolyte. The presence of certain metals enhance the formation of the intercalation compounds. Lithium, aluminum, or nickel fluoride appear to be the best salts for this purpose (92,98). 

Niobium is used as a substrate for platinum in impressed-current cathodic protection anodes because of its high anodic breakdown potential (100 V in seawater), good mechanical properties, good electrical conductivity, and the formation of an adherent passive oxide film when it is anodized. Other uses for niobium metal are in vacuum tubes, high pressure sodium vapor lamps, and in the manufacture of catalysts. 

A dimensionally stable anode consisting of an electrically conducting ceramic substrate coated with a noble metal oxide has been developed (55). Iridium oxide, for example, resists anode wear experienced ia the Downs and similar electrolytic cells (see Metal anodes). 

Good results are obtained with oxide-coated valve metals as anode materials. These electrically conducting ceramic coatings of p-conducting spinel-ferrite (e.g., cobalt, nickel and lithium ferrites) have very low consumption rates. Lithium ferrite has proved particularly effective because it possesses excellent adhesion on titanium and niobium [26]. In addition, doping the perovskite structure with monovalent lithium ions provides good electrical conductivity for anodic reactions. Anodes produced in this way are distributed under the trade name Lida [27]. The consumption rate in seawater is given as 10 g A ar and in fresh water is... 

It is somewhat less corrosion resistant than tantalum, and like tantalum suffers from hydrogen embrittlement if it is made cathodic by a galvanic couple or an external e.m.f., or is exposed to hot hydrogen gas. The metal anodises in acid electrolytes to form an anodic oxide film which has a high dielectric constant, and a high anodic breakdown potential. This latter property coupled with good electrical conductivity has led to the use of niobium as a substrate for platinum-group metals in impressed-current cathodic-protection anodes. 

The copper obtained from this process is about 99% pure, yet this is not pure enough for most uses, especially those involving electrical conductivity. To refine the copper further, it is made the anode of an electrolytic cell containing copper sulfate solution. With careful control of the voltage to regulate the half-reactions that can occur, the copper is transferred from the anode (where it is about 99 % Cu) to the cathode where it can be deposited as 99.999% Cu. At the anode there is oxidation of copper,... 

In an individual molten carbamide, the electrode processes are feebly marked at melt decomposition potentials because of its low electrical conductivity. Both electrode processes are accompanied by gas evolution (NH3, CO, C02, N2) and NH2CN (approximately) is formed in melt. In eutectic carbamide-chloride melts electrode processes take place mainly independently of each other. The chlorine must evolve at the anode during the electrolysis of carbamide - alkali metal and ammonium chloride melts, which were revealed in the electrolysis of the carbamide-KCl melt. But in the case of simultaneous oxidation of carbamide and NH4CI, however, a new compound containing N-Cl bond has been found in anode gases instead of chlorine. It is difficult to fully identify this compound by the experimental methods employed in the present work, but it can be definitely stated that... 

In the following sections, the electrical conductivity, electrochemical activity toward hydrogen oxidation, and the sulfur poisoning behavior of Ni-YSZ cermet anodes will be discussed in detail, together with the effects of various processing procedures and testing conditions. 

Pratihar SK, Baus RN, Mazumder S, and Maiti HS. Electrical conductivity and microstructure of Ni-YSZ anode prepared by liquid dispersion method. In Singhal SC, Dokiya M, editors. Proceedings of the Sixth International Symposium on Solid Oxide Fuel cells (SOFC-VI), Pennington, NJ The Electrochemical Society, 1999 99(19) 513-521. 

Technically important electrochemical reactions of pyrrole and thiophene involve oxidation in non-nucleophilic solvents when the radical-cation intermediates react with the neutral molecule causing polymer growth [169, 191], Under controlled conditions polymer films can be grown on the anode surface from acetonitrile. Tliese films exhibit redox properties and in the oxidised, or cation doped state, are electrically conducting. They can form the positive pole of a rechargeable battery system. Pyrroles with N-substituents are also polymerizable to form coherent films [192], Films have been constructed to support electroactive transition metal centres adjacent to the electrode surface fomiing a modified electrode,... 

EtMgBr solutions in poly(ethylene oxide) containing a small amount of THF or Et20 are electrically conducting. Best conductivity is achieved for an ethylene oxide-Mg ratio of 4, e.g. 0.1 mS cm at 40 °C was found. In contrast, PEO solutions of MgCla, Mg(C104)2 or Mg(SCN)2 show only low electrical conduction below 100 °C. Furthermore, in the presence of EtMgBr solutions Mg can be deposited by cathodic reduction or dissolved by anodic oxidation. Practical apphcation of these solutions are limited by their low thermal and electrochemical stabihty . ... 

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... 

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