Platinum electrodes, plating

The actual values of jo depended slightly on the pretreatment of the solid electrode. Indium-plated platinum electrode. 

To prepare metal hexacyanoferrate films, very frequently the following procedure was followed first a film of the respective metal, for example, cadmium [79], copper [80], silver [81], or nickel [82, 83] was elec-trochemically plated on the surface of a platinum electrode, and that was followed by chemical oxidation of the metal film in a solution of K3[Fe(CN)6], leading to the formation of the metal hexacyanoferrates. The same method has been used to produce films of nickel hexacyanoruthen-ate and hexacyanomanganate using the appropriate anions [83]. It is also possible to perform the oxidation of the deposited metals in solutions containing hexacyano-ferrate(II) by cyclic oxidation/reduction of the latter. In a similar way, films of copper heptacyanonitrosylferrate have been deposited [84]. 

The reactions are carried out in a 200-mL tail-form beaker, with a tightly fitting rubber stopper through which the platinum electrode leads are inserted gas inlet and outlet tubes can be inserted as required. The cathode is a platinum wire carrying a 2 X 2 cm platinum sheet. The anode is a platinum wire onto which a shot of indium is beaten to form a 1 X 1 cm plate. The electrodes are placed 1-2 cm apart in the liquid phase, which is a mixture of organic solvents. 

Proton conductive electrolyte properties of step 2 membranes were determined at 150°C by the impedance measurement using a 13-mm circular-plate-shaped platinum electrode. Testing results are provided in Table 1. 

The surface trough was made of Lucite, 45 X 15 X 1.5 cm. and was divided into two compartments of equal size by a septum of Lucite, 1.5 cm. high. Cooling channels for temperature control were milled into the bottom of the trough. The monolayer was spread inside a paraffined mica frame which floated on the water and was firmly positioned by external mounts. The surface tension was measured with a double-hook torsion balance and a sand-blasted platinum Wilhemy plate. A Beckman model G pH meter with standard glass and KC1 electrodes was used to measure pH. 

It is interesting to conclude this section with an example that, in a sense, brings the chapter full circle. The metallization of plastic materials used as metal substitutes is a process with actual and future commercial potential. Usually, plastics are plated after appropriate sensitization by an electroless process which involves reduction of metal ions (e.g. Ni2+, Cu2+) by chemical rather than electrical means.19 There seems no reason why the reducing agent should not be incorporated in the polymer and Murray and his collaborators101 have demonstrated that copper, silver, cobalt and nickel may each be electrodeposited on to films of [poly-Ru(bipy)2(4-vinylpyridine)2]2+ coated on to platinum electrodes. The metal reductions are mediated by the Ru1 and Ru° states of the polymer. 

One way to determine the metallic composition of an alloy is to use electroplating. Suppose an electrolytic cell is set up with solution of nickel ions obtained from a 6.753-g sample of a nickel alloy. The cell also contains a platinum electrode that has a mass of 10.533 g. Electric current is used to reduce the nickel ions to nickel metal, which is deposited on the platinum electrode. After being plated with nickel, the platinum electrode has a mass of 15.042 g. What is the percentage of nickel in the alloy ... 

As an example, a sample that contains a mixture of copper(II) and nickel(II) salts can be analyzed by first electrolyzing the sample solution under acidic conditions with platinum electrodes such that the copper is plated onto a platinum gauze electrode. Because the solution is acidic, hydronium ion is reduced before nickel ion and there is no interference. After the electrolysis for copper is completed, the electrolysis solution can be neutralized and made basic with ammonia. Having determined the copper and removed it from the platinum electrode, one can electrolyze the remaining basic electrolysis solution to plate nickel on the platinum electrode. 

Mercury-plated electrodes. Platinum can be plated with mercury to form an electrode with many of the properties of a mercury surface. This is done by cleaning a platinum electrode in nitric acid, connecting it as the cathode in perchloric acid solution over a pool of mercury, and then dipping it into the mercury while it is still connected in the circuit. The method works well for plating a planar platinum inlay electrode to give a flat mercury-coated surface, but it can be used for electrodes of any shape.112... 

The theory and application of selective-ion electrodes have been extensively reviewed.143-151 One of the interesting sidelights is the fact that the internal reference electrode may be replaced by an apparent ohmic contact in many instances, as illustrated by Figure 5 Ale for the solid membrane electrode. Thus the glass electrode can be filled with mercury in place of the internal reference electrode,152 or a gold contact that is plated over with copper can be used.153 Likewise, a selective-ion electrode for calcium ion has been described that is coated on a platinum electrode 154 the contact appears to be mainly ohmic. 

Mercury-Plated Platinum Electrode. Anal. Chem. 25, 1351 (1953)-... 

A device for foam dispersity determination by measuring the local foam expansion ratio and the pressure in Plateau borders is illustrated in Fig. 4.4. It consists of a glass container equipped with platinum electrodes and a micromanometer. The container bottom is a porous plate (a sintered glass filter). The pressure Ap is measured with a capillary micromanometer and the expansion ratio is determined by the electrical conductivity of the foam. The manometer and the electrodes are positioned so that to ensure a distance of 1.0-1.5 cm between them and the porous plate. When the distance is small the liquid in the porous... 

The foam is produced in a foam generator. After filling cup 2 with the foam the measuring cell is closed with lid 5 so that the porous plate is in contact with the foam. The foam electrical resistance is measured with platinum electrodes connected to a conductivity meter. 

Figure 8F-1 Layout of a microfabricated structure for combining FIA with a capillary electrophoretic separation, (a) Two glass plates are used in a sandwich structure. The upper plate contains the channel structure (30 p,m wide by 10 p.m deep), and the lower plate contains platinum electrodes for controlling the flow, (b) Samples are injected, mixed with reagents, and carried to a detector. An electrophoretic separation can also be achieved if desired. Detectors have been conductivity, electrochemical, and fluorescence. (Modified from A. Manz, J. C. Fettinger, E. Veipoorte, H. Ludi, H. M. Widmer, and D. J. Harrison, Trends in Analytical Chemistry (TRAC), 1991,10, 144, with permission from Elsevier Science.)...

Figure 9. Schematic diagram of the electrophoresis chamber drawn to scale. Dimensions can be deduced from the top plate, which is 2 cm high. For abbreviations see Figure 8. m, Cellophane membrane A, connector with internal spring H, housing for worm gear. A detailed description is given in Section IV.2.I.a. The bottom electrode compartment is identical to the top one. The distance between the cellophane membrane and platinum electrode is 1 cm. Rapid flushing of the electrode compartments proceeds via f.

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