Metal electrodes nickel

A FIGURE 20.26 Electrolytic cell with an active metal electrode. Nickel dissolves from the anode to form Ni (aq). At the cathode N (aq) is reduced and forms a nickel plate on the steel cathode. 

It is clear from the calculated limiting-current curves in Fig. 3a that the plateau of the copper deposition reaction at a moderate limiting-current level like 50 mA cm 2 is narrowed drastically by the surface overpotential. On the other hand, the surface overpotential is small for reduction of ferri-cyanide ion at a nickel or platinum electrode (Fig. 3b). At noble-metal electrodes in well-supported solutions, the exchange current density appears to be well above 0.5 A/cm2 (Tla, S20b, D6b, A3e). At various types of carbon, the exchange current density is appreciably smaller (Tla, S17a, S17b). 

In this paper, results on the ECH of representative substrates are presented i) in order to illustrate the advantages and the limitations of the ECH at Raney metal electrodes as a method of hydrogenation of organic compounds and ii) in order to discuss some synthetic and mechanistic aspects. The Raney metal electrodes consisted of Raney metal particles embedded in a nickel matrix (1) or dispersed in a lanthanum polyphosphate matrix (2), or of pressed Raney metal alloy of which the outmost layer only has been leached (3). 

Iron, nickel, cobalt, tungsten and chromium do not behave reproducibly due to crystal strain or oxide coatings. Metal electrodes which respond directly to solutions of their own ions are called Class I or first order. ... 

The LEC structure that involves the addition of ionic dopants and surfactants to the printable inks enables the ability to print a top electrode without restriction by the work function of the metal. Silver, nickel, or carbon particle-based pastes are generally the preferred printable electron injecting electrodes however, the shape and size of the particles combined with the softening properties of the solvent can create electrical shorts throughout the device when printed over a thin polymer layer that is only several hundred nanometers thick. For optimal performance, the commercially available pastes must be optimized for printing onto soluble thin films to make a fully screen-printed polymer EL display. 

Potentiometric metal electrodes are rather simple but lack major analytical relevancy due to a number of considerable disadvantages. In particular, they are not very selective, some metals are easily oxidized and still others (Zn, Cd) can dissolve in acidic solutions. Further, certain harder metals such as iron, cobalt and nickel do not provide reproducible potentials. 

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. 

Fig. 11-10. Anodic polarization curves observed for metallic iron, nickel, and chromium electrodes in a sulfuric acid solution (0.5 M H 2SO 4) at 25°C solid curve = anodic metal dissolution current dot-dash curve s anodic oxygen evolution current [Sato-Okamoto, 1981.]...

Commercial catalytic hydrogenations of unsaturated compounds use Raney nickel or—less commonly—Pt catalyst supported on active carbon. Electrocatalytic hydrogenation can be performed at platinized platinum or other platinum-metal electrodes. Adsorbed hydrogen atoms are the active reactant in catalytic as well as in electrocatalytic hydrogenation. 

The inks for screen-printing the electrodes contain the sub-micron metal powder, either a Ag-Pd alloy or a base metal, usually nickel (melting point, 1455°C) but sometimes copper (melting point 1084°C). Palladium (melting point, 1554°C) and silver (melting point, 961 °C) form solid solutions with melting points approximately proportional to the content of the end members. 

An electrochemical cell consists of a nickel metal electrode immersed in a solution with [Ni2+] = 1.0 M separated by a porous disk from an aluminum metal electrode immersed in a solution with [Al3+] = 1.0 M. Sodium hydroxide is added to the aluminum compartment, causing AI(OH)3(s) to precipitate. After precipitation of Al(OH)3 has ceased, the concentration of OH- is 1.0 X 10-4 M and the measured cell potential is 1.82 V. Calculate the Ksp value for Al(OH)3. 

Hydrogen fluoride can be handled in apparatus of suitable metals (copper, nickel, magnesium, or aluminum, which all form a protective fluoride coating, or platinum), or plastic materials [especially polypropylene. Teflon, and polyvinylidene fluoride (Viton)] polychlorotrifluoroethylene (Kel-F) can be made into transparent windows. A capillary for a dropping mercury electrode may be made from Teflon [307]. Hydrogen fluoride is obtained commercially in steel cylinders in a purity of 99.5%. The impurities may be removed by distillation [308] or electrolysis [309]. During the electrolytic removal of water the explosive FoO is formed, which must be taken into consideration [305]. 

An electrolytic cell consists of a pair of inert metallic electrodes in a solution buffered to pH = 5.0 and containing nickel sulfate (NiS04) at a concentration of 1.00 M. A current of 2.00 A is passed through the cell for 10.0 hours. 

Attached to the current collectors of the battery (or to the electrode in metal electrodes) are the tabs. The tabs electrically connect the battery to the can, to transport the electrons and therefore the current. They should also be chemically stable and resistant to corrosion. At the same time, they should have a high electronic conductivity to reduce the internal resistance of the battery. The tabs used in lithium-ion batteries are made of nickel. Other additional components shown in Fig. 1 are the binder and the filler. The binder is the chemical compound used in this case to attach the active material to the current... 

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... 

In the passive state, metal electrodes normally hold extremely small potential-independent dissolution current as shown in Figure 22.7 for metallic iron in acid solution. For some metals such as nickel, however, the passive state changes beyond a certain potential into the transpassive state, where the dissolution current, instead of being potential-independent, increases nearly exponentially with... 

---