Platinum continued anodes

CO (6). Another approach is to develop a CO tolerant anode catalyst such as the platinum/ruthenium electrodes currently under consideration. Platinum/ruthenium anodes have allowed the cells to operate, with a low level air bleed, for over 3,000 continuous hours on reformate fuel containing 10 ppm CO (23). 

Figure 3-6 shows that performance equivalent to that obtained on pure hydrogen can be achieved using this approach. It is assumed that this approach would also apply to reformed natural gas that incorporate water gas shift to obtain CO levels of 1% entering the fuel cell. This approach results in a loss of fuel, that should not exceed 4 percent provided the reformed fuel gas can be limited to 1 percent CO(l). Another approach is to develop a CO-tolerant anode catalyst such as the platinum/ruthenium electrodes currently under consideration. Platinum/ruthenium anodes have allowed cells to operate, with a low-level air bleed, for over 3,000 continuous hours on reformate fuel containing 10 ppm CO (27). 

Platinised-titanium installations have now been in use for 30 years for jetties, ships and submarines and for internal protection, particularly of cooling-water systems . For the protection of heat exchangers an extruded anode of approximately 6 mm in diameter (copper-cored titanium-platinum) has shown a reduction in current requirement (together with improved longitudinal current spread) over cantilever anodes of some 30% . This continuous or coaxial anode is usually fitted around the water box periphery a few centimetres away from the tubeplate. 

Poisoning of platinum fuel cell catalysts by CO is undoubtedly one of the most severe problems in fuel cell anode catalysis. As shown in Fig. 6.1, CO is a strongly bonded intermediate in methanol (and ethanol) oxidation. It is also a side product in the reformation of hydrocarbons to hydrogen and carbon dioxide, and as such blocks platinum sites for hydrogen oxidation. Not surprisingly, CO electrooxidation is one of the most intensively smdied electrocatalytic reactions, and there is a continued search for CO-tolerant anode materials that are able to either bind CO weakly but still oxidize hydrogen, or that oxidize CO at significantly reduced overpotential. 

One energy application of methanol in its early stages of development is the direct methanol fuel cell (DMFC). A fuel cell is essentially a battery in which the chemicals are continuously supplied from an external source. A common fuel cell consists of a polymer electrolyte sandwiched between a cathode and anode. The electrodes are porous carbon rods with platinum... 

The loss of the catalytically active surface of Raney nickel due to recrystallization is a continuously progressing process that can be retarded to some extent in Raney-nickel anodes by dispersing oxide ceramic materials like Zr02 and Ti03 in the nickel matrix. More serious is anodic oxidation for some metals additionally accompanied by dissolution of the catalyst to which even platinum is subject but which is an even more serious hazard for the less noble catalysts as silver and Raney nickel. 

A later method proposed by Oehman [26] produces glycol nitrate and diethylene glycol from ethylene by electrolysis. A platinum wire mesh submerged in an acetone solution of calcium nitrate acts as anode, ethylene being blown through the solution continuously. The cathode space behind the aluminium cathode is filled with a solution of calcium nitrate in nitric acid. At the anode the nitrate ion forms a free radical N03 which combines partially with ethylene to produce nitroglycol (6) ... 

Fig. 6.17. Cyclic voltammograms of o-phenylenediamine (101 M) oxidation for W03 thermal-treated (350°C) anodic films (b) and smooth platinum electrode (c) first sweep (curves 1) and repeated sweep (curves 2) scan rate was 80 mV/cm2. The left picture shows a schematic representation of the morphology of thermal-treated anodic W03 film tungsten support, highly defective oxide (including the continuous donor clusters), moderately doped oxide (non-shaded region), poly-o-phenylenediamine deposits.

Sodium perchlorate is prepared by electrolysis of concentrated solutions of sodium chlorate in cells without diaphragms using platinum anodes and iron cathodes. Electrolysis is continued until some 95 per cent of the initial chlorate... 

The electrolysis is best performed as follows A solution of 13-15 g. calcined soda and 10 g. potassium iodide in 100 cc. water and 20 cc. alcohol is placed in a porous earthenware cylinder with platinum anode. The cathode, of nickel, is surrounded by a strong solution of sodium hydroxide. The electrolysis is carried out at a temperature of 70° C., with a current density at the anode of 1 amp. per 100 sq. cm., and is continued for 2-3 hours. After several hours the iodoform crystallizes out, the current yield being from 60-70 per cent. The chief by-product remaining in the mother liquor is sodium iodate. 

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