Nickel oxide/hydroxide

Electrodes. A number of different types of nickel oxide electrodes have been used. The term nickel oxide is common usage for the active materials that are actually hydrated hydroxides at nickel oxidation state 2+, in the discharged condition, and nickel oxide hydroxide [12026-04-9] NiO OH, nickel oxidation state 3+, in the charged condition. Nickelous hydroxide [12034-48-7J, Ni(OH)2, can be precipitated from acidic solutions of bivalent nickel... 

The discharge-charge reaction of this electrode will be done in two steps but only the first step (Fe <-> Fe2+ + 2e ) is of practical use. For the iron/nickel oxide-hydroxide system these steps (or voltage plateaus) may be written as ... 

A variety of alcohols can be oxidized at the nickel hydroxide electrode. The mediator is presumably a nickel oxide hydroxide, which is fixed to the electrode surface and is continuously reformed at the electrode surface. 

For the less reactive, longer n-alcanols the activation of the nickel hydroxide electrode is necessary (Table 3). For that purpose several layers of black nickel oxide hydroxide are deposited on the electrode surface from a buffered nickel sulfate solution by changing the electrode polarity every 5-10 sec n.isb,20,21)... 

The nickel hydroxide electrode is used since decades in the mckel-iron(Edison)-or nickel-cadmium(Jungner)-storage battery Here the anodes consist mainly of nickel oxide powder pressed into a support and current feeder, whilst for electro-organic oxidations and electroanalytical measurements a thin nickel oxide hydroxide layer on a nickel support is used. 

A nickel surface in contact with an alkaline solution is spontaneously covered with nickel hydroxide Hereby a-nickel hydroxide is formed which on aging is converted to the p-form At about 0.63 V (NHE) a-nickel hydroxide is oxidized to y-nickel oxide hydroxide. At a 80 mV more positive potential the P-form is transformed to p-nickel oxide hydroxide In the cathodic scan nickel oxide hydroxide is reversibly reduced to nickel hydroxide at about 0.54 V. In multiple scan cyclovoltammetry the current increases with each scan indicating an increase of the active electrode surface. 

The individual steps are (a) fast electrochemical conversion of nickel hydroxide to nickel oxide hydroxide, (b) adsorption of the alcohol at the nickel oxide hydroxide surface, whereby a decreasing adsorption with increasing chain length causes a decrease in the rate of oxidation. In the rate determining step (c) hydrogen is abstracted from the adsorbed alcohol by nickel oxide hydroxide to form a a-hydroxy-methyl radical, which is either directly (d) or indirectly (d ) oxidized to the carboxylic acid. 

This is the mechanism of an indirect electrolysis, where the nickel oxide hydroxide acts as an electrocatalyst that is continuously renewed. Some observations, however, are not consistent with this mechanism. The addition of an oxidizable alcohol should lead to an increase of the current for the nickel hydroxide oxidation and a decrease for its reduction This is not the case. The currents for nickel hydroxide and nickel oxide hydroxide remain unchanged, whilst at more anodic potential a new peak for the alcohol oxidation appears. This problem has also been addressed by Vertes... 

The individual steps are (a) the anodically formed nickel oxide hydroxide dehydrogenates the amine to an imine (b) the imine is further dehydrogenated to the nitrile (c) competing with the second dehydrogenation are the hydrolysis of the imine to an aldehyde and its further oxidation to an acid or (d) the condensation with the starting amine to form an azomethine. 

The 1,1-disubstituted hydrazine 53 a is rapidly oxidized in high yield to 54a at the nickel hydroxide electrode (Eq. (15), Table 17). The high reactivity of 53a can be seen from the dissolution of the black nickel oxide hydroxide deposit at the anode. 

Oxidation with nickel peroxide can be executed in protic and in aprotic solvents. With the nickel hydroxide electrode water has to be in the electrolyte, because otherwise the regeneration of nickel oxide hydroxide fails. This limits the choice of solvents. 

The greatest advantage is the electrocatalytic mode of oxidation. In chemical oxidations the reduced form of the oxidant is obtained as by-product. This needs a careful waste treatment to prevent pollutional problems or it has to be regenerated in an additional reaction. At the nickel hydroxide electrode, however, nickel oxide hydroxide is continuously reformed from the hydroxide, so that only electric current is used as reagent. This makes this oxidation also of interest for technical applications. 

A versatile oxidation method for alcohols via electrochemically generated nickel oxide hydroxide is performed at a nickel hydroxide anode in alkaline media85). 

Professor Jaroslaw Lewkowski was born in 1966 in Lodz (Poland). In 1990, he obtained his M.Sc. degree from the University of Lodz, Poland, studying the electrochemical oxidation of 5-hydro-xymethylfurfural derivatives at the nickel oxide/hydroxide electrode. He then joined Professor Skowronski s group from the University of Lodz, Poland, cooperating simultaneously with Professor Descotes team from the University of Lyon 1, France. In 1996, he obtained his Ph.D. degree from the University of Lodz, investigating the selective conversions of furfural, 5-hydroxymethylfurfural, and their derivatives. 

Valuable, however, is the anodic oxidation of primary amines in basic aqueous media at silver oxide, copper oxide, or, more effectively, at nickel hydroxide electrodes to form the nitriles IX in good to excellent yields [6-11]. In this case the primary step in the reaction mechanism is the hydrogen atom abstraction at C(a) by the in situ generated nickel oxide hydroxide, which is formed at about 0.63 V (vs NHE) ... 

Glemser and Einerhand investigated P-NiOOH, y-NiOOH and other nickel oxide hydroxides of higher oxidation state by X-ray powder difffactometry and electron micrography. 

Bale) and Divisek re-evaluated qualitatively equilibrium or rest potentials of solid nickel oxide hydroxides with 2 < z(Ni) < 3.6 measured at ambient temperatures. The experimental data were converted to standard conditions i.e., 25°C, ukoh 1-0, E... 

The redox reaction of nickel hydroxide and nickel oxide hydroxide, the electrochemi-cally active compounds at the positive electrode of a nickel battery, was investigated. The thermodynamics of non-ideal solid solutions were applied to the reversible potential as a function of the state-of-discharge. In a temperature range 5 to 55°C two parameter activity coefficient models perform significantly better than one parameter models. 

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. 

Gu, L., Y. W. Wang, R. Lu, L. Guan, X. S. Peng, and J. Sha. 2014. Anodic electrodeposition of a porous nickel oxide-hydroxide film on passivated nickel foam for supercapacitors. Journal of Materials Chemistry A 2 7161-7164. 

Only about 6% of the produced nickel is applied for the production of nickel compounds. An important one is nickel hydroxide [Ni(OH)2], which is used for nickel-cadmium and nickel-iron batteries. For the production of catalysts the hydroxide, nitrate, sulfate, formate, and carbonate of Ni are used. In the pigment industry nickel oxide, hydroxide, and phosphate are applied and for electroplating nickel sulfate, sulfamate, and tetrafluoroborate are used. 

Oxidation of organic substrates by nickel oxide has been known for more than a century. The substrate scope of the nickd oxide hydroxide oxidation method is quite broad, and includes alcohols, aldehydes, phenols, amines, and oximes. However, an extensive review covering the major part of these reactions demonstrates the requirement of stoichiometric amounts of nickel oxide hydroxide [28]. Recent findings have led to a new oxidation method utilizing catalytic amounts of nickel(II) salts and excess of bleach (5% aqueous sodium hypochlorite) under ambient... 

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