Nickel oxide/platinum electrodes

Jiang SP and Badwal SPS. Hydrogen oxidation at the nickel and platinum electrodes on yttria-tetragonal zirconia electrolyte. J Electrochem Soc 1997 144 3777-3784. 

An in depth study of the deposition mechanism was carried out by Sun et al. who studied the 1 1 [EMIMJCl/ZnCf system at various temperatures on glassy carbon (GC), nickel and platinum electrodes [106], The GC electrode required the largest overpotential for deposition. The stripping process showed a single peak on GC, whereas on Ni two oxidation processes were observed, separated by ca. 0.6V. Itwas proposed that the more positive oxidation process corresponded to the dissolution of an intermetallic compound formed during electrodeposition. 

D.M. Zhou, H.X. Ju, and H.Y. Chen, Catalytic oxidation of dopamine at a microdisc platinum electrode modified by electrodeposition of nickel hexacyanoferrate and Nafion. J. Electroanal. Chem. 408, 219-223 (1996). 

Electrodes may be classified into the following two categories as shown in Fig. 4-3 one is the electronic electrode at which the transfer of electrons takes place, and the other is the ionic electrode at which the transfer of ions takes place. The electronic electrode corresponds, for instance, to the case in which the transfer of redox electrons in reduction-oxidation reactions, such as Fe = Fe + e,occurs and the ionic electrode corresponds to the case in which the transfer of ions, such as Fe , , = Fe, occiirs across the electrode interface. Usually, the former is found with insoluble electrodes such as platinum electrodes in aqueous solution containing redox particles and the latter is found with soluble metal electrodes such as iron and nickel. In practice, both electron transfer and ion transfer can take place simultaneously across the electrode interface. 

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]. 

Pyridinethiol (70) can be coupled at the nickelhydroxide electrode (75 °C, K2CO3 in water) in 91 % yield to 2,2 -dithiodipyridine (71) (Eq. (21)) An oxidation temperature above 70 °C is of advantage, at 65 °C the yield of 71 drops to 64 %. The dimerization at the nickel hydroxide electrode leads to higher yield than the direct oxidation at the platinum electrode in methanol (78 % 71) . 71 is used as condensation reagent for the preparation of peptides and macrolides... 

Suitable materials for the anode in electrochemical perfluorinations are nickel plate, nickel foam5 or nickel oxide laminated metals.6 Materials for the cathode are nickel or steel. Platinum or rhodium is commonly used29 for partial electrochemical fluorination. Nickel electrodes are... 

Methods. The differential heats of adsorption of reagents and the differential heat of their interaction on the nickel oxide surface were measured in a Calvet microcalorimeter with a precision of 2 kcal. per mole. The apparatus has been described (18). For each adsorption of a single gas, small doses of gas are allowed to interact with a fresh nickel oxide sample (100 to 200 mg.) placed in the calorimeter cell maintained at 30°C. At the end of the adsorption of the last dose, the equilibrium pressure is, in all cases, 2 torr. Duplication of any adsorption experiment on a new sample gives the same results within 2 kcal. per mole of heat evolved and 0.02 cc. of gas adsorbed per gram. Electrical conductivities of the nickel oxide sample are measured in an electrical conductivity cell with platinum electrodes (1) by a d.c. bridge. 

Electrochemical techniques are the most widely used methods to obtain nickel(III) complexes. Generally the oxidation of the nickel(II) complexes is performed in acetonitrile solutions under an inert atmosphere using a platinum electrode.3052 A tetraalkylammonium salt, usually the perchlorate, is employed as supporting electrolyte (ca. 0.1 M). The complete procedure is often carried out in the dark at ca. 5°C to prevent possible photoreduction reactions.3053-3055... 

At a platinum electrode, highly purified FLINAK has a voltammetric window extending from about +1.5 to -2.0 V vs. the nickel reference electrode [7]. The positive limits of the alkali halide melts discussed herein arise from the oxidation of halide ions, whereas the negative limits are due to reduction of the alkali metal ions. Because chloride ion is substantially easier to oxidize than fluoride ion, the potential window of the LiCl-KCl melt is approximately 1.5 V smaller than that for FLINAK. 

If (23) is selected as the dihalosilane, a convenient way of modifying the nickel surface is available.64 The electrochemical properties of the treated nickel electrode are very similar to those of a similarly derivatized platinum electrode for example, both are equally effective in the elec-trocatalytic oxidation-reduction of solution ferrocene. Normally oxidation of the nickel surface would be a competing process ultimately rendering the electrode passive. The surface modification clearly eliminates this problem and opens up the possibility of using surface modified inexpensive metals as electrodes. 

The electrical conductivity was measured by W. H. Ross, who found that in all cases the conductivity of the salt soln. was increased with time, especially with the more dil. soln. This is due to the decomposition of the salts under the influence of the platinum-black of the electrodes with polished electrodes, the effect is considerably smaller. The base itself is oxidized even more rapidly than the salts. The soln. are in all cases decomposed by the platinum electrodes, and G. M. J. MacKay showed that tin does not decompose the soln. at all, while copper decomposes the soln. completely. The order in which the metals were found to decompose the soln. is tin, platinum, silver, nickel, mercury, and copper. The electrical conductivity of hydroxylamine, using tin electrodes, in terms of mercury at 18°, with v vols. of soln. per mol, is as follows ... 

Electrodes Anode Platinum Platinum/ carbon Platinum / carbon Platinum/ ruthenium Platinum Nickel Nickel/ nickel oxide Zinc anode... 

Passivity.—It is now a matter of common knowledge that platinum, like iron, cobalt, and nickel, exhibits passivity under certain conditions.5 Possibly this is due to the formation of a superficial layer of oxide which protects the underlying metal from attack. This explanation is supported by the fact that during the electrolysis of platinum chloride solution with platinum electrodes, the anode becomes slightly coated with oxide,6 and the same is true when dilute sulphuric acid containing from 2-5 to 10 per cent, of acid is similarly electrolysed.7... 

The major dehciency of the oxygen electrode reaction is its low exchange current density (about 10 A/cm on a smooth surface) in acid electrolytes on even the best-known electrocatalyst (a platinum-chromium alloy). This value is about six orders of magnitude lower than that for the hydrogen electrode reaction in the same electrolyte. The reaction is about three orders of magnitude faster on smooth platinum or nickel oxide surfaces in an alkaline medium as compared to acid. The... 

Some of the more exotic electrode materials are nickel coated with manganese, tungsten or ruthenium oxides for positive electrodes. These metals give quicker action for the part of the reaction that occurs at the positive electrode. Nickel plated platinum can be used on the negative... 

The crystal structure of bis(NN-di-isobutyldithiocarbamato)nickel(ii). [Ni(S2-CNBu 2)2], shows that nickel is approximately square planar and co-ordinated by two symmetric bidentate ligands (Ni—S = 2.20 A) the ligand symmetry approximates to 2- The reduction mechanism of a series of nickel(ii) dithiocarbamates has been investigated in DMSO at the mercury electrode it is claimed to involve a dissociation to a nickel species which is more easily reduced than the nickel(ii) dithiocarbamate. An e.p.r. study of the reversible electrochemical reduction of nickel(ii) diethyldithio-carbamates in the presence of 2,2 -bipyridyl show that a bipy radical anion is formed initially. Ligand alkylation occurs when ao -dibromo-o-xylene is added to bis-(NiV-diethyldithiocarbamato)nickel(ii). The electron-transfer properties of 16 nickel(ii) dithiocarbamate complexes have been studied in acetone at a platinum electrode. Their oxidation is difficult and irreversible the overall process is ... 

Electrodes were fabricated with catalyst layers containing platinum-ruthenium alloys and platinum-ruthenium oxide. Membrane electrode assemblies were fabricated with such cells, and the performance was evaluated in a full cell configuration. Although ruthenium oxide is a proton conductor and is expected to enhance the rate of proton transport from the interface during methanol oxidation, no noticeable improvement in activity of the catalyst layer was observed by addition of ruthenium oxide. The role of other metal oxides such as tungsten oxide will be investigated next year, along with evaluation of non-noble metal catalysts based on nickel, titanium, and zirconium. 

By operating at about 650 °C, the kinetics of the oxygen reduction reaction at the positive electrode are sufficiently accelerated that it is no longer necessary to use platinum-based electrocatalysts. Usually, the positive electrode is fabricated from lithiated nickel oxide (Li Nii 0, where 0.02[Pg.211]

Several metal oxides (platinum, gold," nickel, copper, ) and cobalt phtalo-cyanine have been employed as surface bound mediators for carbohydrate detection. In a dc amperometric mode of operation detectors based on these mediators exhibit a significant loss of response with time and/or exposure to analyte. Various potential pulse programs have circumvented this stability problem, but at the expense of sensitivity and complexity of the instrumentation. Silver electrodes coated with electrogenerated silver oxide exhibit electrocatalytic activity with respect to carbohydrate oxidation. This paper describes our efforts to utilize an electrode as a carbohydrate detector in a dc amperometric mode. 

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