Electro-oxidation-electroreduction

For these low-temperature fuel cells, the development of catalytic materials is essential to activate the electrochemical reactions involved. This concerns the electro-oxidation of the fuel (reformate hydrogen containing some traces of CO, which acts as a poisoning species for the anode catalyst methanol and ethanol, which have a relatively low reactivity at low temperatures) and the electroreduction of the oxidant (oxygen), which is still a source of high energy losses (up to 30-40%) due to the low reactivity of oxygen at the best platinum-based electrocatalysts. 

At the equilibrium potential, E = Eq, the electro-oxidation and electroreduction rates are equal (Tred< o = oxcr) such that... 

A peculiar example of heterocoupling has been found in the electroreduction of a mixture of pyrrole (60) and 2,4,7-trinitrofluoren-9-one (59), which leads to the formation of two Meisenhemer anions (the major isomer (structure 61) from attack at position 3, the minor one from attack at position 1) arguably via coupling of the two radical anions (see Scheme 42) [131], Electro-oxidation of such anions gives a black polypyrrole film which differs from that obtained by the normal electro-oxidative polymerization of pyrrole (compare Section 6.3.4). 

It was previously shown that oxidation produced a radical cation which could be detected by ESR [111, 112] provided the 4 position was fully substituted. If the 4 position contained a hydrogen atom, then the initial oxidation was followed by deprotonation with the formation of a neutral radical which could undergo further oxidation or dimerisation. In-situ spin trapping using PBN demonstrated the presence of radical intermediates in the electro-oxidation of substituted 1,4-dihydropyridines. That the trapped radicals were the deprotonated neutral radical, and not the primary radical cation, was demonstrated by comparison of the ESR parameters with those of the spin adduct produced by electroreduction of A-methylpyridine ion cations, where only the neutral dihydropyridyl radical would be produced. The work of Volke and co-workers clearly demonstrates how spin trapping may be applied to the study of more complex organic electrode reactions and how comparison of ESR spectra generated from different precursors may be used to reveal the nature of the trapped radical. 

As direct electro-oxidation, direct electroreduction can be fulfilled through direct electrolysis of a substrate (e.g., chlorobenzenes or phenols) in a solvent-supporting electrolyte (e.g., tetraethylammounium bromide in methanol) at an electrode (e.g., graphite) surface (Farwell, Beland, Geer, 1975). 

Polarographic waves are observed only in those molecules or ions— organic or inorganic—which are capable of electro-reduction or -oxidation at the dropping mercury electrode. In cases of electroreduction the waves and currents are termed cathodic, and in cases of electro-oxidation, anodic. The borderline dividing the cathodic from the anodic currents is the zero line of the galvanometer, corresponding to the currentless state. Cathodic waves are then represented above, and anodic waves below, this zero line. 

Photocatalytic decomposition of alcohol Electro-oxidation of hydrogen Electroreduction of oxygen Ammonia synthesis Carbon monoxide methanation Carbon monoxide methanation Carbon monoxide oxidation Propene hydrogenation Benzene hydrogenation Oxidation of ethylene Coal liquefaction Electroreduction of oxygen Dehydrogenation of butadiene... 

Electroreduction cathodic processes Electro-oxidation anodic processes Other electrochemical processes... 

Park K, Pintauro PN, Baizer MM, Nobe K (1985) Flow rate studies of the paired electro-oxidation and electroreduction of glucose. J Electrochem Soc 132 1850-1855... 

Senthurchelvan et al. [1020] studied a unique algorithm for continuous electroreduction of Cr(VI) in toxic wastes, an important present need due to environmental considerations. A P(Py) film was used in its reduced form to transfer electrons spontaneously, and thus reduce, Cr(VI). After allowing for a predetermined contact time between the Cr(VI) solution and the reduced P(Py), usually in the minutes regime, the P(Py) was then regenerated through electro-oxidation, as shown in Eq. (24,2). 

An element A (which may be O, S, N, or H) is adsorbed on a metal M in the form of a monoatomic layer, with a valence state equal to zero [denoted A dsCM)]. The adsorption of A from a species dissolved in aqueous solution may be an electro-oxidation or an electroreduction reaction, depending on the valence state of A in the dissolved species. 

A copper(O) complex, electro-generated from Cu(acac)2, is able to undergo an oxidative addition with benzyl and allyl bromides. Further reduction leads to the coupling products bibenzyl and 1,5-hexadienes Methyl-3-hexene-l,6-dicarb-oxylate can be prepared from butadiene and CO by electroreduction if di-Fe dicyclopentadienyl tetracarbonyl is used as redox catalyst Electro-generated low-valent tungsten species are able to reductively dimerize benzaldehyde to stilbene according to Eq. 83. The reduction potential was controlled at the third wave of the WClg catalyst (V = -1900 mV/SCE)... 

Zhang, J., A.B.P. Lever, and W.J. Pietro (1995). Electrocatalytic activity of a graphite electrode coated with hexadecachlorophthalocyanato iron(II) toward sulfide oxidation, and its possible application in electroanalysis. Can. J. Chem. 73, 1072-1077. Christensen, P.A., A. Hamnett, and A.V.G. Muir (1988). An in-situ FTIR study of the electroreduction of CO2 by CoPc-coated edge graphite electrodes. J. Electro anal. Ctem. 241(1-2), 361-371. 

To make the B-site coordination more flexible and hence to improve electro-catalytic performance, Mn and Ga were introduced to replace Ti in La4Srg Tii2038 z-based fuel electrodes. Mn supports p-type conduction in oxidizing conditions and has been previously shown to promote electroreduction under... 

Oxygen electroreduction/ EDAX, XRD NixCo3 04 spinel KOH solution Electro-deposition of oxide films by spraying on Ni foil The ratio of oxygen molecules reduced via the direct 4e pathway with respect to those reduced via indirect 2+2 electron pathway depends on x. The ratio is maximum for X = 0 and 0.6 < x < 1.2 Heller-Ling etal. (1997)... 

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