Platinum electrodes preparation

Figure 25-20. Potential differences measured on air/hydrogen, water vapor cells with platinum electrodes prepared with different layer thickness resistivity ratios d/p (a), or after annealing at different temperatures between 500 and 1300 °C (b) [73].

A neat form of apparatus much smaller than Kohl-rausch s, consists of an ebonite cup and rod fitted with platinum electrodes prepared in the usual manner. The rod can be moved vertically over the cup by means of micrometer screws, and the distance between the electrodes read off on a divided scale by a vernier. Quantities of solutions as small as 3 cc maybe employed. 

Mertz, and A. J. Bard, A stable surface modified platinum electrode prepared by coating with electroactive polymer, J.Am.Chem.Soc, 100 3222 (1978). 

It should be noted that platinum electrode prepared in a standard way and in aqueous 0.5N solution of potassium chloride gives the potential ranging from 150 to 350 mv, but most often about 230 to 280 mv (pH of solution approximately 6.65), The silver-silver chloride electrode s own potential in the same solution is 5 mv. 

C. HIO is prepared by oxidation of iodine with perchloric acid, nitric acid, or hydrogen peroxide or oxidation of iodine in aqueous suspension to iodic acid by silver nitrate. Iodic acid is also formed by anodic oxidation at a platinum electrode of iodine dissolved in hydrochloric acid (113,114). 

It is known that tropylium may be prepared from tropylidene via hydride abstraction by PhgC or MegC carbonium ions therefore, it is very likely that here too the dehydrogenation is a hydride transfer from the 1,5-dione to an acceptor. A similar dehydrogenation of chromanones to chromones, with triphenylmethyl perchlorate was reported. A study of the electrooxidation of 1,5-diones on a rotating platinum electrode showed that 1,5-diaryl-substituted diones afford pyrylium salts in these conditions and that the half-wave potentials correlate with yields in chemical dehydrogenations. 

Prepare 250 mL of 0.02 M potassium dichromate solution and an equal volume of ca 0.1 M ammonium iron(II) sulphate solution the latter must contain sufficient dilute sulphuric acid to produce a clear solution, and the exact weight of ammonium iron(II) sulphate employed should be noted. Place 25 mL of the ammonium iron(II) sulphate solution in the beaker, add 25 mL of ca 2.5M sulphuric acid and 50 mL of water. Charge the burette with the 0.02 M potassium dichromate solution, and add a capillary extension tube. Use a bright platinum electrode as indicator electrode and an S.C.E. reference electrode. Set the stirrer in motion. Proceed with the titration as directed in Experiment 1. After each addition of the dichromate solution measure the e.m.f. of the cell. Determine the end point (1) from the potential-volume curve and (2) by the derivative method. Calculate the molarity of the ammonium iron(II) sulphate solution, and compare this with the value calculated from the actual weight of solid employed in preparing the solution. 

The indicator electrode must be reversible to one or the other of the ions which is being precipitated. Thus in the titration of a potassium iodide solution with standard silver nitrate solution, the electrode must be either a silver electrode or a platinum electrode in the presence of a little iodine (best introduced by adding a little of a freshly prepared alcoholic solution of iodine), i.e. an iodine electrode (reversible to I-). The exercise recommended is the standardisation of silver nitrate solution with pure sodium chloride. 

The first reported electroorganic synthesis of a sizeable amount of material at a modified electrode, in 1982, was the reduction of 1,2-dihaloalkanes at p-nitrostyrene coated platinum electrodes to give alkenes. The preparation of stilbene was conducted on a 20 pmol scale with reported turnover numbers approaching 1 x 10. The idea of mediated electrochemistry has more frequently been pursued for inorganic electrode reactions, notably the reduction of oxygen which is of eminent importance for fuel cell cathodes Almost 20 contributions on oxygen reduction at modified... 

Zhan [61] reported the use of an oscillopolarographic method for the determination of primaquine phosphate and other drugs in pure form and in pharmaceutical preparations. The sample solution was mixed with potassium bromide and 6 M hydrochloric acid and the mixture was titrated with 0.1 M sodium nitrite. A micro platinum electrode and a platinum electrode were used as indicators and reference electrodes, respectively. The mean recoveries were 96.88-99.88%. Results agreed well with those obtained by the Chinese Pharmacopoeia method. 

Complicating matters further is the fact that the platinum electrode, the standard tool for measuring Eh directly, does not respond to some of the most important redox couples in geochemical systems. The electrode, for example, responds incorrectly or not at all to the couples SO -HS-, O2-H2O, CO2-CH4, NOJ-N2, and N2-NH4 (Stumm and Morgan, 1996 Hostettler, 1984). In a laboratory experiment, Runnells and Lindberg (1990) prepared solutions with differing ratios of selenium in the Se4+ and Se6+ oxidation states. They found that even under controlled conditions the platinum electrode was completely insensitive to the selenium composition. The meaning of an Eh measurement from a natural water, therefore, may be difficult or impossible to determine (e.g., Westall, 2002). 

Cha, S. Y., and Lee, W. M. Performance of proton exchange membrane fuel cell electrodes prepared by direct deposition of ultrathin platinum on the membrane surface. Journal of the Electrochemical Society 1999 146 4055 060. 

The function of an immuno-electrode [28] containing a model antibody (Concanavalin A) fixed in a polymeric film on a platinum electrode is probably based on other effects than those utilized in ISEs. Immuno-electrodes suitable for direct determination of antibodies were prepared by fixing a conjugate of an ionophore and an immunogen (for example the compound of dibenzo-18-crown-6 with dinitrophenol) in a PVC membrane. This system responded to the antibody against dinitrophenol [52, 53]. 

Sometimes, semiconductivity depends on the type of a structural phase that arises from synthesis. Thus, in the case of (TCNQ) Cu the semiconducting phase is thermodynamically disfavored. To prepare this semiconductor, Harris et al. (2005) proposed to perform the reduction of TCNQ in acetonitrile at glass-carbon, gold, or platinum electrode in the presence of Cu. This allows the electrocrystallization of sparingly soluble TCNQCu semiconducting phase to occur by a nucleation... 

V-Acylsaccharins prepared by treatment of the sodium salt of saccharin with acyl chlorides were reduced by 0.5 molar amounts of sodium bis(2-methoxyethoxy)aluminum hydride in benzene at 0-5° to give 63-80% yields of aliphatic, aromatic and unsaturated aldehydes [1108 Fair yields (45-58%) of some aliphatic aldehydes were obtained by electrolytic reduction of tertiary and even secondary amides in undivided cells fitted with platinum electrodes and filled with solutions of lithium chloride in methylamine. However, many secondary and especially primary amides gave 51-97% yields of alcohols under the same conditions [130]. 

At IREQ, besides the participation in the field tests run by the engineers of Hydro-Quebec (12), the main effort has been to tackle fundamental problems in the field of electrocatalysis (18-22) and of anodic oxidation of different potential fuels (23-26). A careful and extensive study of the electrochemical properties of the tungsten bronze has been carried out (18-20) the reported activity of these materials in acid media for the oxygen reduction could not be reproduced and this claim by other workers has been traced back to some platinum impurities in the electrodes. Some novel techniques in the area of electrode preparation are also under study (21,22) the metallic deposition of certain metals on oriented graphite show some interesting catalytic features for the oxygen reduction and also for the oxygen evolution reaction. 

In a subsequent study by Robertson, Murphy, and coworkers, polymer 23 was synthesized by anodie polymerization on platinum electrodes and eompared to polymer 19 in order to determine the effect of the position of the linkage of the dithiolene to thiophene moieties. In this study, the researchers used the salts [Bu4N][ll] and [Bu4N][16] in MeCN to prepare the respective polymers 19 and 23. Surprisingly, the polymerization of the anion 11 resulted in films exhibiting different electroehemieal response than that observed for 19... 

The series of disposable parts are merely placed on the stage to achieve simplicity of preparation and disposal prior to and after use of the system (Fig. 1 inset) (rrcNote 4). For reuse, a series of platinum electrode units are fabricated separately. The conveyer automatically set the electrode units in designated positions on the parts at the electrode storage site. The electrode units are washed and returned to the site after the electrophoresis procedures are performed. 

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]. 

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