Platinum anodes

Platinum Platinum-coated titanium is the most important anode material for impressed-current cathodic protection in seawater. In electrolysis cells, platinum is attacked if the current waveform varies, if oxygen and chlorine are evolved simultaneously, or if some organic substances are present Nevertheless, platinised titanium is employed in tinplate production in Japan s. Although ruthenium dioxide is the most usual coating for dimensionally stable anodes, platinum/iridium, also deposited by thermal decomposition of a metallo-organic paint, is used in sodium chlorate manufacture. Platinum/ruthenium, applied by an immersion process, is recommended for the cathodes of membrane electrolysis cells. ... 

The additivity principle was well obeyed on adding the voltammograms of the two redox couples involved even though the initially reduced platinum surface had become covered by a small number of underpotential-deposited mercury monolayers. With an initially anodized platinum disk the catalytic rates were much smaller, although the decrease was less if the Hg(I) solution had been added to the reaction vessel before the Ce(lV) solution. The reason was partial reduction by Hg(l) of the ox-ide/hydroxide layer, so partly converting the surface to the reduced state on which catalysis was greater. 

James SD. 1969. Multilayer oxide films on anodized platinum. J Electrochem Soc 116 1681-1682. 

We saw in Section 3.1 that CEC consists in substituting the anode platinum wire by a gold him mechanically squeezed between two flat insulahng substrates and that the physical conflnement favours a quasi-2D gro vth. We can here raise the question, what would happen if we directly use free large surface anodes as substrates We next see two examples, using gold plates and silicon wafers as electrodes. 

It is usual to operate an aqueous-medium fuel cell under pressure at temperatures well in excess of the normal boiling point, as this gives higher reactant activities and lower kinetic barriers (overpotential and reactant diffusion rates). An alternative to reliance on catalytic reduction of overpotential is use of molten salt or solid electrolytes that can operate at much higher temperatures than can be reached with aqueous cells. The ultimate limitations of any fuel cell are the thermal and electrochemical stabilities of the electrode materials. Metals tend to dissolve in the electrolyte or to form electrically insulating oxide layers on the anode. Platinum is a good choice for aqueous acidic media, but it is expensive and subject to poisoning. 

Electrodes Anode Platinum Platinum/ carbon Platinum / carbon Platinum/ ruthenium Platinum Nickel Nickel/ nickel oxide Zinc anode... 

Most of the electrolyses in sulfuric acid have been performed without control of the potential. In polarographic work the mercury pool has been used for anodic and cathodic reactions As anode, platinum or lead dioxide have been employed as cathode, lead, mercury, or platinum. 

Dithianes and gemdithioacetals could be alternatively oxidized indirectly by means of the redox catalysis method. The technique appeared to be particularly mild and mainly avoided inhibition and adsorption phenomena relative to the anode platinum interface. Thus aromatic hydrocarbons (e.g. 9,10-diphenylanthracene) [83] and judiciously substituted triphenylamines [84] afford quite stable cation radicals used homogeneously as oxidants. Their standard potential, E°x, will determine the rate of electron exchange with the concerned sulfur compound. The cleavage of a C—S bond in any dithiane can be regarded as fast enough to draw the redox catalysis process to the indirect oxidation. 

The properties of sllane-derlvatlzed Iridium and anodic Iridium oxide (AIROF) electrodes have been studied by cyclic voltammetry In tetraethylammonlum perchlorate/acetonitrile solutions. Both electrodes react with silanes such as dlchlorosilylferrocene (DCSF) to give persistently bonded silylferrocene monolayers based on geometric area. This contrasts with the behavior of anodized platinum (Pt/PtO), which gives considerable polymerization with DCSF, resulting in layers of variable and unpredictable thickness. 

A comparison of iridium, anodized platinum (Pt/PtO), and anodized iridium (AIROF) as derivatizable electrodes shows iridium to be the most useful for the study of surface-bound molecules. 

Electrodes anode (platinum, n-type silicon, conducting glass, (1,5-7)... 

Zheng XW, Zhang ZJ, Guo ZH, Wang Q (2002) Flow-injection electrogenerated chemiluminescence detection of hydrazine based on its in situ electrochemical modification at a jne-anodized platinum electrode. Analyst 127(10) 1375-1379. doi 10.1039/b203172h... 

Electrodes anode (platinum, n-type silicon, conducting glass, stainless steel, gold/ glassy Carlson) cathode (copper) Electrolytes copper sulfate, acetonitrile + p-toluenesulfonoc acid (HTSO), lithium jjerchlorate, sodium perchlorate, sulfuric acid... 

Figure 12.18 Schematic design oj an Isoelectrqfocusing apparatus. (A) Anode platinum ring, (B) Cathode platinum ring. (C) Waterjacket to maintain the temperature, (D) Power pack, and(E) Value to errqjty the column. The density gradient is shown by light and heavy shadowing. P, and Pj are two protein bands electrofocussed according to their isoelectric pH values.

Laconti et al. (2003) proposed that H2O2 can be formed at the anode side via the reaction of crossover O2 with Hj on the anode platinum catalyst, through the following three steps ... 

The indicator electrode was an anodized platinum wire while the reference electrode placed in the flow of the titrant was of pure platinum. This electrode system was first suggested by Harlow et al. [3] and showed good reproducibility. We also tried palladium and iridium, either pure or anodized, but the results were less satisfactory. The electrodes were connected to a Beckman model H-2 pH meter. With this setup, series of titrations can be carried out without disconnecting between consecutive titrations thus, the inert atmosphere can easily be maintained. 

LaConti et al. proposed a mechanism where oxygen molecules permeate through the membrane from the cathode side, and are reduced at the anode platinum catalyst to form (LaConti 1982 LaConti et al. 1977, 2003) in the early R D era for space missions. This mechanism for H Oj formation in a PEMFC is shown schematically in Fig. 4a. 

For the conventional MEA, Hemion SH50 membrane was used. The Cathode platinum loading was 0.6 mg cm , and the anode platinum loading was 0.3 mg cm" ... 

Fig. 10 Durability of MEAs at 120°C, 50% RH, 0.2A cm", and 200kPa. Reactant, Hj/air, utilization 50 50 cathode platinum, 0.6 mg cm anode platinum 0.3 mg cm A (Reproduced with permission from Endoh (2006). Copyright 2006, The Electrochemictd Society, Inc.)...

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