Cathodes platinum-containing

According to U.S. Patent 2,966,493, the 2,3-bis-(3-pyridyl)-2,3-butanedlol used as the starting material may be prepared as follows. A solution of 1,430 g of 3-acetyl-pyridine in 7,042 ml of a 1 N aqueous solution of potassium hydroxide is placed into a cathode chamber containing a mercury cathode with a surface of 353 cm and is separated from an anode chamber by an Alundum membrane. As anode a platinum wire is used and the anolyte consists of a 1 N solution of aqueous potassium hydroxide which Is replenished from time to time. 

The only species which need be present in the cell initially are the reactants, zinc atoms, and Cu2+ ions. In other words, the anode of the cell must be made of zinc and the solution surrounding the cathode must contain Cu2+ ions. On the other hand, the products of the reaction, copper atoms and Zn2+ ions, need not be present when the cell is set up. A platinum wire can be substituted for the copper rod copper ions plate out as readily on platinum as on copper. Any positive ion which does not react with zinc can replace the Zn2+ ions surrounding the zinc electrode. A solution of Na2S04 or KN03 works as well as a solution of ZnS04. 

FLINAK is purified by treatment with the HF released by ammonium bifluoride (NH4HF2) the HF converts oxide impurities in the melt to H20 [7]. In this purification procedure, the fluoride salt mixture is combined with 15 wt% NH4HF2 and heated to about 500°C in a graphite crucible. The molten mixture is poured into a platinum container and heated to 750°C. Hydrogen is passed through the molten mixture for approximately 2 days. Further purification can be achieved by con-trolled-potential electrolysis at an applied potential of about 3 V between a tungsten cathode and glassy carbon anode. 

More effort has been devoted to studies of 02 production. In this case, the cathode compartment contains [Ru(bipy)3]2+ and an electron acceptor such as [S208]2-,354-356 [Co(C204)3]3, 351 [Co(NH3)5Cl]2+,353,357 or Tl3+,353 and a platinum or carbon cathode. The pH of the anode compartment depends not only on the oxidation potential of the [Ru(bipy)3]3+, which can be varied by use of substituted bipyridyls, but also on the overpotential of the anode material for 02 production. 

An electrochemical reaction, the reduction of benzoquinone, is exemplarily described. An electrochemical micro structured reactor is divided into a cathode and anode chamber by a Nafion hollow-fiber tube. The anode chamber is equipped with a platinum electrode and the cathode chamber contains the analyte and carbon or zinc electrodes. Current density and flow rate are controlled to maximize current efficiency as determined by analysis of the formed hydroquinone by an electrochemical detector. Hydroquinone is extracted subsequently in a micro extractor from the resulting product stream [84],... 

The platinum electrode can be improved by an active electrolytic process forming a platinum black surface. The reduced polarization impedance is due to an increased effective metal surface area (fractal surface). The electrode is prepared in an electrolyte containing (e.g., 3% platinum chloride), with the platinum as the cathode. Platinum black is deposited on the surface, and also here there are optimum values for current density and quantity of electricity a current density of about 10 mA/cm and a quantity of electricity (charge) of about 30,000 mA s/cm is recommended (Schwan, 1963). Best results are obtained if the platinum surface is sandblasted before platinum black deposit. However, the surface may be fragile, and a protein layer formed with tissue contact may easily smooth the micro-rough surface and increase polarization impedance. Platinum black electrodes are best stored in distilled water and short-circuited (Schwan, 1963). 

The catalyst is platinum-based for both the anode and cathode. To promote hydrogen oxidation, the anode uses either pure platinum metal catalyst or, as is common in most modem PEFC catalysts, a supported platinum catalyst, typically on carbon or graphite for pure hydrogen feed streams. For other fuels, such as reformate (containing H2, CO2, CO, and N2), the desired catalyst is an alloy of platinum containing mthenium. Oxygen reduction at the cathode may use either the platinum metal or the supported catalyst. 

Long-term fuel cell tests were conducted using electrodes of 50 cm with the Pt/ Pd/C cathode catalyst containing 77 pg cm of platinum (0.21 gp kW ) and 373 ig cm" of palladium. A commercial Pt/C electrocatalyst (180pg cm of platinum) was used for the anode. Figure 5a illustrates the trace of the ceU voltage at a constant... 

The electrolytic cells shown ia Figures 2—7 represent both monopolar and bipolar types. The Chemetics chlorate cell (Fig. 2) contains bipolar anode/cathode assembhes. The cathodes are Stahrmet, a registered trademark of Chemetics International Co., and the anodes are titanium [7440-32-6] Ti, coated either with mthenium dioxide [12036-10-17, RUO2, or platinum [7440-06-4] Pt—indium [7439-88-5] Ir (see Metal anodes). Anodes and cathodes are joined to carrier plates of explosion-bonded titanium and Stahrmet, respectively. Several individual cells electrically connected in series are associated with one reaction vessel. 

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