Carbon electrochemical oxidation

Studies of electrochemical carbon oxidation in carbonate melts at 700°C were performed by Weaver et al. (1981) at the Stanford Research Institute, Menlo Park, California. They used rods of different carbon materials as electrodes. The electrode potentials were measured relative to a gold reference electrode in an atmosphere of carbon dioxide mixed with oxygen at the same temperature. The electrodes proved to be more active the lower the degree of crystallinity of the initial powder (from which the rods were pressed). The electrodes had open circuit potentials around 1.1 V. At a current density of lOOmA/cm the potential of the most active sample was 0.8 V (and 0.9 V when the temperature was raised to 900°C). 

Li et al. (2010) tested four different Australian raw coals as fuels in direct carbon MCFCs. They found that the cell performances are highly dependent on a coal s intrinsic properties, in particular its chemical composition and concentration of oxygen-containing surface groups. Impurities such as AI2O3 and Si02 lead to an inhibitive effect, whereas CaO, MgO, and Fc203 exhibit a catalytic effect on the electrochemical carbon oxidation reaction. 

A similar inhibition was found also for electrochemical CO oxidation. In COad stripping experiments, numerous potential cycles up to IV were necessary to remove all COad from a smooth Ru(OOOl) surface [Zei and Ertl, 2000 Lin et al., 2000 Wang et al., 2001]. CO bulk oxidation experiments under enforced mass transport conditions on polycrystalline Ru [Gasteiger et al., 1995] and on carbon-supported Ru nanoparticle catalysts [Jusys et al., 2002] led to similar results. Hence, COad can coexist with nonreactive OHad or Oad species on Ru(OOOl) at lower potentials (E < 0.55 V) [El-Aziz and Ribler, 2002]. 

Electrochemical anodic oxidation of amides and N-alkyllactams can be carried out with IV-hydroxy-phthalimide as mediator. Oxidation takes place predominantly at the endocyclic carbon a to the nitrogen. The susceptibility of five-membered rings to oxidation is much higher than that of six-membered rings. 

Instead of nucleophiles such as H2O, MeOH, RNH2 and halide ions, both the aryl group and olefinic double bond will react with an electrogenerated phenoxonium ion to give carbon-carbon coupled products. In particular, electrooxidative coupling reactions of a,ft)-diarylalkanes leading to cyclic diaryl ethers have been known to take place in a radical or cationic manner depending on the oxidation potential, the nature and location of substituents, the solvent systems and other factors, as cited in many books Electrochemical carbon-carbon bond formations will be described here. 

The adsorption of alcohols, aldehydes, and carbon oxides on metal electrocatalysts has been extensively studied because of the significance of their oxidation reactions for electrochemical energy generation (7,9,81,195). Particular attention has been payed to the surface intermediates of methanol oxidation on platinum. At least two adsorption states have been assigned to methanol, a weak one possibly associated with physisorption (196) and one or more states arising from dissociative strong adsorption of the reactant (797, 198). Breiter (799) proposed a parallel scheme for methanol oxidation... 

Also corrosion problems of the carbon support have been considered as a cause of electrocatalyst durabihty loss [32], in particular carbon oxidation can occur through electrochemical oxidation at the cathode, with formation of CO2 (C -I- 2H2O = CO2 -I- 4H -F 4e ), or through water gas shift reaction, with the production of CO (C H2O = CO H2). Both these routes are catalyzed by Pt [56, 57] and subtract caibon useful for platinum loading, with consequent metal sintering and decrease of the electrochemical surface area [58]. 

Phenol can be detected electrochemically by oxidation at a carbon paste electrode (Wehmeyer et al., 1983). A convenient means of determining a low concentration of phenol in a small volume of sample is by liquid chromatography with electrochemical detection (LCEC). A diagram of the LCEC system is shown in Fig. 2. The sample is injected by means of 20-pl sample loop into a 5-cm column slurry-packed with lO-pm Cjg stationary phase. The column serves to separate the peak for phenol from other assay constituents in order to achieve a better detection limit. The phenol is detected by oxidation in a thin-layer electrochemical cell with a carbon paste working electrode. 

The electrochemical reactions of carbon oxide groups have been described as the most likely redox ixocesses on the carbon surfaces by numerous researchers [185, 186,188] particularly, the quinone and hydroquiiume r ox system. This assumption has b n corroborated by the characterization of the surface functionalities conventional techniques. 

A known solntion to this problem is creating and ntUizing power installations with coal-fired fuel cells (FC) [1-3]. As a rule, coal is first gasified, and then the prodncer gas is fed to fuel cells. However, carbon oxide, which is formed by partial oxidation of coal and hydrocarbons, is an extremely unstable compound that recombines, under specific conditions, to solid carbon, i.e. fuel soot, which clogs the FC pores and damages the electrochemical equipment. 

HCl Strong acid, nonoxidizing Metals above H in the electrochemical series Oxides, sulfides, carbonates, phosphates Organic salts... 

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