Platinum gauze

A fuel cell is simply a device with two electrodes and an electrolyte for extracting power from the oxidation of a fuel without combustion, converting the power released directly into electricity. The fuel is usually hydrogen. The principle of a fuel cell was first demonstrated by Sir William Grove in London in 1839 with sulphuric acid and platinum gauze as an electrocatalyst, and thereafter there were very occasional attempts to develop the principle, not all of which were based on sound scientific principles , as one commentator put it. 

The electrodes are made of platinum gauze as the open construction assists the circulation of the solution. It is possible to use one of the electrodes as stirrer for the solution, but special arrangements must then be made for connection of the electrolysis current to this electrode, and an independent glass-paddle stirrer or a magnetic stirrer offer a simple altemative.Typical electrodes are the Fischer type depicted in Fig. 12.4 a glass tube is slid into... 

In electrogravimetry, also called electrodeposition, an element, e.g., a metal such as copper, is completely precipitated from its ionic solution on an inert cathode, e.g., platinum gauze, via electrolysis and the amount of precipitate is established gravimetrically in the newer and more selective methods one applies slow electrolysis (without stirring) or rapid electrolysis (with stirring), both procedures either with a controlled potential or with a constant current. Often such a method is preceded by an electrolytic separation using a stirred cathodic mercury pool, by means of which elements such as Fe, Ni, Co, Cu, Zn and Cd are quantitatively taken up from an acidic solution whilst other elements remain in solution. 

The preparation is electrolytic. The anode consists of a few inches of thin platinum rod, to one end of which a 1 X f in. piece of platinum foil is attached. This is surrounded by a hollow cylinder of platinum gauze of diameter 1 in. and length 1 - in. The other end of the platinum rod is attached to an electric stirrer. ... 

Turyan and Mandler [483] determined ppt levels of mercury in seawater by first converting mercury salts to elemental mercury using stannous chloride, the mercury was then trapped on gold deposited on platinum gauze and released by heating prior to determination by inductively coupled plasma mass spectrometry. 

Debrak and Denoyer [484] determined mercury at the ppt level in seawater by the addition of tin chloride to produce hydrogen vapour, and trapping on gold-platinum gauze, prior to heating and detection of the mercury released by inductively coupled plasma mass spectrometry. 

Cu, In, Ga, and Se are codeposited from the solution at room temperature in a three-electrode cell configuration, where the reference electrode is a platinum pseudo-reference, the counter electrode is platinum gauze, and the working electrode is the substrate. The substrates typically used are glass, DC-sputtered with about 1 pm of Mo. In all experiments, the applied potential is -1.0V versus the Pt pseudo-reference electrode. The corresponding current density range for the deposition is 5 to 7 mA/cm2. 

Platinum deposition techniques, 79 157 Platinum dichloride, 79 655 Platinum-divinyltetramethyldisiloxane complex, in silicone network preparation, 22 563 Platinum films, 79 658 Platinum gauze catalyst, 77 180-181 Platinum-group metal compounds, 79 635-667 analysis of, 79 637 economic aspects of, 79 635-636 health and safety factors related to, 79 658... 

The working electrode generally consists of a cylindrical platinum gauze or a mercury pool thereby offering the largest surface area possible to the redox process. 

Figure 7 shows a typical electrolysis cell with a platinum gauze working electrode. Eventually the platinum gauze can be replaced by a mercury pool working electrode. The volume of solution contained in such a cell is about 30-50 ml. 

Figure 7 Typical cell for electrolysis with a working platinum gauze electrode...

Compounds 52, 53, 57, 58, and 69-72 were measured in 10% aqueous acetonitrile with 0.2 M BU4NBF4 as supporting electrolyte. All other compounds were measured in dichloromethane with 0.2 M BU4NBF4 as supporting electrolyte. A platinum electrode or a platinum gauze basket were the working electrode and all potentials are reported against the saturated calomel electrode (SCE) with a reference potential of 0.0 V. Values of for 57, 58, 70, 72, and 78 are actually values of E the reversible peak potential. All other values of are irreversible peak potentials. 

Another oxidative cyclization to afford a nitrogen heterocycle is illustrated in Scheme 12 [33]. This reaction was accomplished using a platinum gauze electrode at a controlled potential of -t-1.8 V versus Ag/AgCl. The reaction proceeded through the initial oxidation of the amide. Evidence... 

Anodic oxidation of enaminone 10 was performed at the platinum gauze electrode in methanol solution containing LiC104 in a divided cell at controlled potential. After passage of 1.2F/mol two major products 11 and 12 were isolated in 50 and 20% yields respectively (Scheme 12). Oxidation of the enaminone 10 is initiated by electron loss from the dimethylamino moiety to... 

The difference between the two reactions of Scheme 2.9 may also be considered in terms of the complete electron transfer in both cases. If the a-nitrostilbene anion-radical and metallocomplex cation-radical are formed as short-lived intermediates, then the dimerization of the former becomes doubtful. The dimerization under electrochemical conditions may be a result of increased concentration of reactive anion-radicals near the electrode. This concentration is simply much higher in the electrochemical reaction because all of the stuff is being formed at the electrode, and therefore, there is more dimerization. Such a difference between electrode and chemical reactions should be kept in mind. In special experiments, only 2% of the anion-radical of a-nitrostilbene were prepared after interruption of controlled-potential electrolysis at a platinum gauze electrode. The kept potential was just past the cathodic peak. The electrolysis was performed in the well-stirred solution of trani -a-nitrostilbene in AN. Both processes developed in this case, namely, trans-to-cis conversion and dimerization (Kraiya et al. 2004). The partial electrolysis of a-nitrostilbene resulted in redox-catalyzed equilibration of the neutral isomers. 

An example of the first mechanism is provided by the oxidation of ammonia to nitric oxide over a platinum gauze catalyst, where reaction is initiated by raising the temperature of the gauze by some external means once reaction has been started in this way, it is self-sustaining (autothermal), heat being transferred to the cold reactants by conduction through the gauze and by radiation. 

The phenomenon under consideration was studied systematically in the beginning of the 19th century. In 1815, Davy performed experiments that dealt with catalytic combustion on platinum gauzes. The term catalysis , however, was introduced by Berzelius in 1836. He first defined a catalyst (Berzelius, 1836) as a compound, which increases the rate of a chemical reaction, but which is not consumed during the reaction. This definition was later amended by Ostwald (1853-1932) in 1895 to involve the possibility that small amounts of the catalyst are lost in the reaction or that the catalytic activity is slowly decreased A catalyst is a substance that increases the rate of approach to equilibrium of a chemical reaction without being substantially consumed in the reaction. It was more than a century after Berzelius first definition that Marcel Prettre s introduced the notion of yield The catalyst is a substance that increases the rate of a chemical transformation without modifying the yield, and that is found intact among the final products of the reaction. ... 

The catalytic oxidation of ammonia by air over platinum gauze at 900 °C gives nitric oxide (reaction 9.12), which is then oxidized to nitric acid by air and liquid water in a nitrous gas absorber (reactions 9.13 and 9.14) ... 

Fig. 7.33. Microelectrode of radius, r, surrounded by a basket of platinum gauze of radius R.

The industrial process is carried out with platinum gauze as the catalyst at 750—900°C. Selectivities of 95—97% are reported for this extremely fast chemical reaction. The main by-product is N2, and only traces of N20 are formed. The kinetics were reviewed by Dixon and Longfield [101], since when the subject has not received much attention. 

It may also be prepared by electrolysis of the alkali thiocyanates in aqueous or alcoholic solution, using a platinum gauze anode and a silver cathode. On evaporation under reduced pressure, thiocyanogen is obtained as a viscous oil, solidifying at —70° C.4... 

Of interest is the use of this system as both solvent and reactant in a voltaic cell. If two platinum gauze electrodes are immersed in liquid chlorocuprates and a potential is applied, the cell begins charging- At less than 1/of full charge, the potential stabilizes at 0.85 V and remains at that value until the cell is fully charged. The half-reactions for charging are... 

Solid samples can be introduced by means of a piece of notched hypodermic tubing fitted with a handle. The tubing is filled with sample and then introduced into the heated port. A similar device is now marketed by the Hamilton Company. Solid samples can be introduced on small portions of stainless steel or platinum gauze. The sample is quantitatively transferred onto the gauze by placing the gauze in an indentation on a Teflon plate. 

SOLION. A small electrochemical oxidation-reduction cell consisting of a small cylinder containing a solution and divided into sections by platinum gauze, porous ceramics, or other materials. A type of solion for detecting sound waves consists of a potassium iodide-iodine solution m which the iodide ions are oxidized to truodide ions at the anode, and the reverse process occurs at the cathode. The cell is constructed so that the sound waves cause agitation of the solution between die electrodes, and... 

For ammonia oxidation on platinum gauzes under atmospheric pressure, using the analogy between diffusion and heat transfer, an equation was obtained (156) equivalent to the following ... 

Co304 pellets used in practice are of 4-5 mm in size. Thus, they are much larger than the diameter of wires in platinum gauzes. For this reason, in contrast to the reaction on gauzes, the reaction on Co304 pellets under atmospheric pressure is characterized by the Reynolds number much larger than 1, the Reynolds number being defined by Re = ul/v where u is the linear velocity of the stream, / is the characteristic dimension, v is the kinetic viscosity coefficient. The thickness of the diffusion layer for such pellets is... 

The need to reduce metal losses during ammonia oxidation led to the development of a number of specialized technologies. The first was the substitution of alloy gauzes for pure platinum gauzes. Handforth and Tilley (143) demonstrated that platinum gauzes containing 10-20% Rh lost far less metal than pure platinum screens and were actually somewhat more active than pure... 

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