Platinum-titanium dioxide electrode

Electropolyraerization is useful and has been successfully applied to 4-vinylpyridine complexes and to 4-methyl-4 -vinyl-2,2 -bipyridyl.52 Vinylferrocene (vide infra) has been polymerized on to platinum, glassy carbon and titanium dioxide electrodes by introduction to a radiofrequency argon plasma discharge. Electropolymerization and plasma polymerization are likely to be of value to produce copolymers on electrode surfaces. 

At the end of 1960 s, Honda and Fujishima found that in a photochemical cell employing titanium dioxide and platinum electrodes, irradiation of the titanium dioxide electrode resulted in splitting of water into hydrogen and oxygen (18,19). This work has had an extraordinarily strong impact for the research on the photochemical action of various semiconductors inducing evolution of hydrogen from water as well as new catalytic reactions (20). 

Fujishima and Honda reported the splitting of water by the use of a semiconductor electrode of titanium dioxide (rutile) connected through an electrical load to a platinum black counter-electrode. Irradiation of the Ti02 electrode with near-UV light caused electrons to flow from it to the platinum counter-electrode via the external circuit. 

The electrocatalytic behavior of olefins was studied by Zanta et al. (2000) at thermally prepared ruthenium-titanium- and iridium-titanium-dioxide-coated anodes. The aliphatic olefins were shown to be inactive in the region before oxygen evolution, while aromatic ones showed one or two oxidation peaks, and the catalytic activity seemed to be the same for both substrates. However, as for platinum anodes, voltammetric studies and FTIR analyses have also shown the formation of a polymeric film that blocks the surface of the electrode and decreases its activity. 

Platinum anodes have a limited operational range of oxidation potentials and thus attention has focused on Sn02-coated titanium materials. The tin oxide material, when doped with Sb (approximately 5%) to impart the appropriate electrical conductivity, has oxygen overpotentials some 600 mV greater than those of platinum. Tin oxide gives higher oxidation efficiencies to those of platinum, lead dioxide, ruthenium and iridium oxide (DSA) electrodes and is reported to be stable to corrosion during anodic oxidation. 

Enhanced performance was also reported for anode modification with conductive polymers. A commonly used conductive polymer, polyaniline, can increase the current densities of MFC anodes. But it is also susceptible to microbial attack and degradation [39]. Schroder et al. [18] reported that a platinum electrode covered with polyaniline achieved a current density up to l.SmAcm in an MFC. Modification of polyaniline can improve its performance and stability, such as fluorinated PANI [40], PANI/carbon nanotube (CNT) composite [41], and PANI/titanium dioxide composite [42]. 

Platinum and carbon are frequently used as counter electrode materials for both anode and cathode. Platinum is resistant to corrosion while carbon is cheap and can be discarded after use. Nickel is a suitable counter cathode material in aqueous solution because of the low overpotential for hydrogen evolution. Titanium coated with platinum and then over coated with mthenium dioxide is a stable counter anode material with a low overpotential for oxygen evolution. 

ELECTRODE. Either ul two substances having different electromotive activity that enables an electric current to flow in the presence of an electrolyte. See also Electrolyte. Electrodes are sometimes called plates or terminal. Commercial electrodes are made uf a number of materials that vary widely in electrical conductivity, i.e.. lead, lead dioxide, zinc, aluminum, copper, iron, manganese dioxide, nickel, cadmium, mercury, titanium, and graphite research electrodes may be calomel mercurous chloride), platinum, glass or hydrogen. 

The most popular electrode materials for reduction are mercury, lead, titanium, and platinum. The choice of anode is limited because most metals are anodically corroded. In the laboratory, most of the electrodes are made of platinum, gold, or carbon. Exotic anodes such as lead dioxide or DSA (Dimensionally Stable Anode such as Ti/Ru02) have been developed for organic or chlorine electrochemistry. 

A variety of electrode reactions14 can occur at the anode. Some of them result in the formation of gases, corrosive attacks on most electrode materials, or oxidative attacks on the membrane in contact with the anolyte solution. Platinum is too cosily for use as an anode material, but titanium or tantalum conted with ex ire ms ly thin (mjcrainchas) layers of platinum has bean used. Lead dioxide deposited on and within graphite has been used also. Oxidation-resistant rnsmbranes (fluorocarbon-based) often are used adjacent to the anolyte solution even though they are expansive. 

Titanium covered by platinum or by dioxide of manganese, ruthenium, iridium or other substances is most commonly used as an anode. Graphite and graphite covered with lead dioxide have also been used as anodes. Under some conditions, high pH and absence of salts in the anolyte, nickel can be used as the anode. Stainless steel is commonly used as the cathode. If current reversal is employed, the same material, platinized titanium or graphite, is used for both electrodes. Electrode chambers should be flushed with a large flow of rinse solution in order to remove the electrode reaction products. 

Other alkali-metal chlorates are produced by analogous technology while sodium and potassium bromate are produced electrolytically starting both from bromide ion and bromine solutions. The production of bromate is, however, a very small-scale process and the cells have not been optimized to any extent for example while cells with lead dioxide and platinized titanium have been described, some plants still use solid platinum electrodes The mechanism of bromate formation is identical to that described for chlorate by reactions (5.10)—(5.13) the kinetics are, however, different. The hydrolysis of bromine is slower than chlorine but the disproportionation step is much faster (by a factor of 100) and it is therefore advisable to use a more alkaline electrolyte, about pH 11. 

Metal wire mesh, e.g., of platinum, or sintered metal may also be used as an electrode material. A membrane surface that is soft due to a pretreatment may be suitable. Combiiung it with graphite felt assures an optimal contact by pressing them together. For example, titanium wire mesh or also porous sintered titanium metal coated with lead dioxide was used as an anode and graphite felt as a cathode for the previously mentioned reaction of y-butyrolactone [4]. 

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