Electrochemical reactions, nickel hydroxide

In normal battery operation several electrochemical reactions occur on the nickel hydroxide electrode. These are the redox reactions of the active material, oxygen evolution, and in the case of nickel-hydrogen and nickel-metal hydride batteries, hydrogen oxidation. In addition there are parasitic reactions such as the corrosion of nickel current collector materials and the oxidation of organic materials from separators. The initial reaction in the corrosion process is the conversion of Ni to Ni(OH)2. 

For the dehydrogenation of CH—XH structures, for example, of alcohols to ketones, of aldehydes to carboxylic acids, or of amines to nitriles, there is a wealth of anodic reactions available, such as the nickel hydroxide electrode [126], indirect electrolysis [127, 128] (Chapter 15) with I , NO, thioanisole [129, 130], or RUO2/CP [131]. Likewise, selective chemical oxidations (Cr(VI), Mn02, MnOJ, DMSO/AC2O, Ag20/Celite , and 02/Pt) [94] are available for that purpose. The advantages of the electrochemical conversion are a lower price, an easier scale-up, and reduced problems of pollution. 

The detection step involves electrochemical oxidation at a nickel electrode. This electrode has been applied to measurements of glucose (4), ethanol (5), amines, and amino acids (6,7). The reaction mechanism involves a catalytic higher oxide of nickel. The electrolyte solution consists of 0.1 M sodium hydroxide containing 10-4 M nickel as suspended nickel hydroxide to ensure stability of the electrode process. The flow-injection technique offers the advantages of convenience and speed in solution handling and ready maintenance of the active electrode surface. 

A great advantage of electrochemical reactions compared with chemical conversions is the effective contribution to pollution control. The direct electron transfer from the electrode to the substrate avoids the problem of separation and waste treatment of the frequently toxic end products of the chemical oxidants or reductants. Furthermore, by electrodialysis, organic acids or bases can be regenerated from their salts without the use of sulfuric acid or sodium hydroxide, for example, which lead to the coproduction of sodium salts or sulfates as waste [79]. At the same time, inorganic acids and bases, necessary for chemical production, are provided by this process. An application of electrodialysis has been demonstrated in the preparation of methoxyacetic acid by oxidation of methoxyethanol at the nickel hydroxide electrode [80]. Finally, unwanted side products can be converted into the wanted product, which increases the economy of the process and reduces the problem of waste separation and treatment. This is accomplished in the manufacture of chloroacetic acid by chlorination of acetic acid. There the side product dichloroacetic acid, formed by overchlorination, is cathodically converted to chloroacetic acid [81]. 

In all the above methods for oxidizing carbohydrates a stoichiometric oxidant is added to the reaction mixture. This can be avoided by using an electrochemical oxidation. A nickel hydroxide electrode has been applied for oxidizing isopropylidene-protected carbohydrates in aqueous base [26]. While secondary hydroxy groups fail to react under these conditions, the hemiacetal at the anomeric center is oxidized to the lactone in good yield [26]. 

McBreen comprehensively reviewed nickel hydroxide battery electrodes, the solid state chemistry of nickel hydroxides, and the electrochemical reactions of the Ni(OH)21 NiOOH couple. Any critical discussion of the thermodynamic data of nickel oxide hydroxides with higher oxidation states has to refer to this splendidly written account of nickel solid state electrochemistry. 

Kowal A, Port SN, Nichols RJ (1997) Nickel hydroxide electrocatalysts for alcohol oxidation reactions an evaluation by infrared spectroscopy and electrochemical methods. Catal Today 38(4) 483-492... 

Nickel hydroxide exists in four different forms a-Ni(OH)2, p-Ni(OH)2, p-NiOOH, and y-NiOOH. p-Ni(OH)2 and p-NiOOH are known as stable forms. The electrochemical reaction of NiO, Ni(OH)2 and NiOOH is described as below ... 

Electrochemical Processes The charged positive electrodes of these batteries contain NiOOH, an oxide hydroxide of trivalent nickel, and the negative electrodes contain metallic cadmium or iron (M). As a rule, KOH solution serves as the electrolyte. The main current-producing reactions on the electrodes and in the cell in general can be written as... 

The actual cell voltage is about 1.5 V, it does not depend on the actual pH-value of the electrolyte solution as obvious from the absence of protons and hydroxide ions in the cell reaction equation. It slightly depends on the source of the used manganese dioxide. Initially naturally occurring manganese dioxide was used. The battery required a quality of less than 0.5% copper, nickel, cobalt, and arsenic to avoid undue corrosion of the zinc electrode. Currently synthetic manganese dioxide is prepared either by chemical (CMD) or electrochemical (EMD) procedures. For improved electrical conductivity graphite or acetylene black are added. Upon deep... 

The three basic steps in the palladium-catalysed Suzuki-Miyaura reaction involve oxidative addition, transmetalation, and reductive elimination. A systematic study of the transmetalation step has found that the major process involves the reaction of a palladium hydroxo complex with boronic acid, path B in Scheme 3, rather than the reaction of a palladium halide complex with trihydroxyborate, path A. A kinetic study using electrochemical techniques of Suzuki—Miyaura reactions in DMF has also emphasized the important function of hydroxide ions. These ions favour reaction by forming the reactive palladium hydroxo complex and also by promoting reductive elimination. However, their role is a compromise as they disfavour reaction by forming of unreactive anionic trihydroxyborate. A method for coupling arylboronic acids with aryl sulfonates or halides has been developed using a nickel-naphthyl complex as a pre-catalyst. It works at room temperature in toluene solvent in the presence of water and potassium carbonate. ... 

The electrochemical oxidation is carried out with an electrolyte containing potassium hydroxide (1.4 mol dm ) and potassium manganate (100-250 g dm" at 60 C at an anode made from nickel or monel (Ni-Cu). The cathode is iron or steel. The anode reaction requires an unusually low current density between 5 and 15 mA cm Even so, some oxygen evolution occun and the current yields are only between 60 and 90% the material yield generally exceeds 90% ... 

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