Nickel oxide electrodes

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... 

Sometimes two discharge voltage plateaus are seen on nickel oxide electrodes. Early observations are documented in previous reviews [2, 9]. Normally, nickel oxide electrodes have a voltage plateau on discharge in the potential range of 0.25-0.35V vs. Hg/HgO. The second plateau, which in some cases can account for up to 50% of the capacity, occurs at -0.1 to - 0.6 V. At present there is a general consensus that this second plateau is not due to the presence of a new, less-active, compound [91-94]. Five interfaces have been identified for a discharging NiOOH electrode [93]. These are... 

Oxygen evolution occurs on nickel oxide electrodes throughout charge, on overcharge, and on standby. It is the anodic process in the self-discharge reaction of the positive electrode in nickel-cadmium cells. Early work in the field has been reviewed [9], No significant new work has been reported in recent years. 

Nickel oxide anodes are another example for a relatively simple oxide electrocatalyst used rather widely in the oxidation of organic substances (alcohols, amines, etc.) in alkaline solutions at relatively low anodic potentials (about +0.6 V RHE). These processes, which occur at an oxidized nickel surface, are rather highly selective. As an example, we mention the industrial oxidation of diacetone-L-sorbose to the corresponding acid in vitamin C synthesis. This reaction occurs at nickel oxide electrodes with chemical yields close to 100%. 

The most extensive study of the nickel oxide electrode is that of McBreen et a/.,83 who employed an in situ cell in a transmission mode (see cell in Fig. 17). The study of nickel oxide is complicated by the numerous species present and their interconversion. McBreen... 

Other examples of conversion using a nickel oxide electrode are the oxidation of benzyl alcohols. A nickel foam electrode was used for oxidation [18] in this case and the mechanism was studied by... 

R = C5Hii, R2 = H R =C4Hg, R2 = Me Scheme 3 Oxidation of aliphatic alcohol at the nickel oxide electrode. 

Scheme 4 Oxidation of allyl alcohol at the nickel oxide electrode.

Electrochemically generated nickei(lll) oxide, deposited onto a nickel plate, is generally useful for the oxidation of alcohols in aqueous alkali [49]. The immersion of nickel in aqueous alkali results in the formation of a surface layer of nickel(ll) oxide which undergoes reversible electrochemical oxidation to form nickel(lll) oxide with a current maximum in cyclic voltammetry at 1.13 V vj. see, observed before the evolution of oxygen occurs [50]. This electrochemical step is fast and oxidation at a prepared oxide film, of an alcohol in solution, is governed by the rate of the chemical reaction between nickel oxide and the substrate [51]. When the film thickness is increased to about 0.1 pm, the oxidation rate of organic species increases to a rate that is fairly indifferent to further increases in the film thickness. This is probably due to an initial increase in the surface area of the electrode [52], In laboratory scale experiments, the nickel oxide electrode layer is prepared by prior electrolysis of nickel sulphate at a nickel anode [53]. It is used in an undivided cell with a stainless steel cathode and an alkaline electrolyte. 

Electrochemically generated nickel(lll) oxide is approximated as NiO(OH). Analytical figures obtained for the chemically prepared oxide approximate to NiO(OH).H20. The material behaves as a radical source and the initial step in the oxidation of alkanols is radical attack with removal of the a-hydrogen atom. This is followed by an electron transfer from the carbon radical so generated, see Scheme 8.4 [54], The same process also attacks aldehydes in the gem-diol form. The nickel oxide electrode also attacks nitrogen-containing compounds (p. 281). 

Conversion of primary alcohols, as an emulsion in aqueous sodium hydroxide, to the carboxylic acid at a pre-fomied nickel oxide electrode, ref. [59]. 

The nickel oxide electrode is generally useful for the oxidation of alkanols in a basic electrolyte (Tables 8.3 and 8.4). Reactions are generally carrried out in an undivided cell at constant current and with a stainless steel cathode. Water-soluble primary alcohols give the carboxylic acid in good yields. Water insoluble alcohols are oxidised to the carboxylic acid as an emulsion. Short chain primary alcohols are effectively oxidised at room temperature whereas around 70 is required for the oxidation of long chain or branched chain primary alcohols. The oxidation of secondary alcohols to ketones is carried out in 50 % tert-butanol as solvent [59], y-Lactones, such as 10, can be oxidised to the ketoacid in aqueous sodium hydroxide [59]. 

Oxidation of primary amines at a nickel oxide results in the formation of a nitrile. Formation of the nickel oxide electrode was discussed on p, 270. The rate determining stage ss the reaction between electrochemically formed nickel(ni) ox-... 

The influence of zinc intercalation on processes in nickel oxide electrode and on the long life of Ni-Zn batteries was also studied. 

Solvent extraction offers unique advantages among separation techniques. A system based on extraction into a polymer [poly(vinyl chloride)] as solvent was examined here because of possible advantages in speedy simplicity, sample size, solvent handlingy etc.f especially when coupled with flow injection and an amperometric detector. Solutes examined included salicylic acid and 8-hydroxy quinoline. The apparatus typically consisted of 0.8-mm i.d. X 170-cm coiled tubing that could be connected directly to the injection loop of a flow-injection amperometric detector system containing a nickel oxide electrode. 

Fig. 6.11 Six-cell nickel-meial hydride batiery. 1. positive cap, connected to the nickel oxide electrode 2, can, connected to metal hydride electrode and serving as negative terminal 3. separator 4. cathode 5, anode 6. plastic battery case which contains interconnected cells and electronic management system. (By permission of Duracell.)...

New, high-density nickel oxide electrode materials, coupled with nonwoven nickel-fiber current collectors, have significantly improved the performance of the nickel electrode even in the nickel-cadmium cells [5j. The alloys used to form hydride, which capture and release hydrogen in volumes up to nearly a thousand times their own, include rare-earth/nickel alloys (generally based on LaNis and called AB5)... 

As suggested for the OER at nickel oxide electrodes (128, 303), it is probable that high oxidation states of the Co metal ion of the oxide film or layer, on which the OER is proceeding, are involved as intermediate states (mediator sites) in the oxygen evolution processes, together with OH and O species at the surface of the oxide. A mechanistic view of the involvement of such Co metal ion species can be written (302) as follows, as for nickel oxide ... 

Oxidation of the methyl group in o-toluenesulfonamide at a nickel oxide electrode in aqueous carbonate leads to saccharin in 40% yield [68]. 

Some details are given by Merck in Ref. 112. The electrochemical oxidation is performed in alkaline solution using nickel or nickel oxide electrodes [113]. Hydrogen evolved at the cathode can be used for the hydrogenation of D-glucose to D-sorbitol, the first step in the vitamin C synthesis by the Reichstein route. Obviously, Merck doesn t use electrodes with high specific areas but prefers to stop the electrolysis at a conversion rate of 90%. The oxidation is completed with sodium hypochlorite solution. 

Nickel oxide electrodes constitute the positive plates of several storage systems (among which nickel-zinc, nickel cadmium, nickel metal-hydride, sodium-nickel chloride) [16]. In recent years, the high-specific energy and specific power of Ni-Zn systems has increased the interest in their use for electric vehicles with respect to the past years, when their application was essentially limited by a short cycle life. 

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