Nickel hydroxide, layered

There is a rich literature where just temperature dependence of electrochemical parameters is of interest. It is no wonder that large part of those papers cannot reaUy be classified to belong to thermoelectrochemistry. In fact, many experiments have been done just to improve the efficiency of common processes by means of certain temperature variation. The majority of these types of publications are found in battery research [94-118]. Theoretical considerations from a fundamental point of view are a rare exception [94]. Nearly all papers are dealing with special battery types. Nickel batteries of the Ni-Cd or the NiMH type actually are not preferably in the focus of interest. All actual papers are directed to the nickel hydroxide layer at the positive electrode [95,96]. Also, the lead-acid battery is considered scarcely at present [27]. 

In acidic electrolytes only lead, because it forms passive layers on the active surfaces, has proven sufficiently chemically stable to produce durable storage batteries. In contrast, in alkaline medium there are several substances basically suitable as electrode materials nickel hydroxide, silver oxide, and manganese dioxide as positive active materials may be combined with zinc, cadmium, iron, or metal hydrides. In each case potassium hydroxide is the electrolyte, at a concentration — depending on battery systems and application — in the range of 1.15 - 1,45 gem"3. Several elec-... 

Layered nickel hydroxide can be used as an electrode for alkaline secondary cells. To improve its properties, modification has been carried out by incorporation of other metal elements to form Ni/M LDHs, including Co [221], Zn [222], Al [223], Cr or Mn [224] and Fe [225]. For example, Chen et al. reported the electrochemical performance of Al-substituted layered a-... 

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. 

The lower amines have been oxidized in similar yields to nitriles at silver oxide and copper oxide anodes Activation of the electrode by deposition of a nickel hydroxide oxide layer is less essential than with alcohols due to the higher reactivity... 

The voluminous nickel hydroxide, that is produced from the oxidant, tends to adsorb organic compounds. This renders the isolation of the product sometimes difficult. In the electrolysis, however, the oxidant forms only a thin layer at the anode surface, which causes no problems in the work-up. 

The many varieties of practical nickel electrodes can be divided into two main categories. In the first, the active nickelous hydroxide is prepared in a separate chemical reactor and is subsequently blended, admixed, or layered with an electronically conductive material. This active material mixture is... 

It was as early as 1946 that de Lange and Yisser (1) published their finding that the precipitate formed on adding alkali hydroxide to a suspension of diatomaceous earth in a nickel salt solution is not merely a mixture of nickel hydroxide and diatomaceous earth, but that a reaction has taken place between the hitherto supposed inert carrier and the nickel compound. They ascertained the occurrence of such a reaction from the very great increase in accessible surface and the more difficult reduction of the reaction-product as compared with that of nickel hydroxide, and, on the basis of their X-ray work, suggested the formation of nickel hydrosilicates having a layer structure. Further, they assumed that after reduction... 

SYNTHESES OF MDOED LAYERED NICKEL HYDROXIDE MANGANESE OXIDES BY HYDROTHERMAL INTERCALATION REACTION AND EXFOLIATION-RESTACKING HYDROTHERMAL REACTION... 

Since dehydration produces a change of color from light green for the hydroxide to yellowish green for the oxide, it has been possible to observe that decomposition does not take place simultaneously at the surface of all the particles in a thick layer ( 10 mm) of nickel hydroxide. On the contrary, a well-defined reaction interface moves downward in the powdered sample at a constant rate. It has been ascertained that the reaction rate is then proportional to the interface area and that the apparent reaction order for the dehydration process changes if the shape of the pan containing the reactants is modified (23). However, the... 

Nickel electrodes are usually based on nickel hydroxides. Several forms of nickel hydroxides and oxyhydroxides are involved in the electrochemical process of nickel electrodes, which have been described in literature as a-Ni(0H)2i j8-Ni(OH)2. 7-Ni(0H)2, -NiOOH and y-NiOOH . The three divalent nickel hydroxides have different chemical compositions, but all of them have a lattice structure of alternate layers, differing in the relative spacing of hexagonal structure. The starting material for the formation of the alkaline electrode is the a-form hydroxide which is denoted as a-Ni(OH)2.xH2O,2 where x varies between 0.5 and 0.7. 

It can be obtained by the electrochemical precipitation of NiCNOjJj- water of hydration is an integral part of this compound and is believed to be responsible for the much larger distance between the hydroxide layers when compared to that in jS-Ni(0H)2, which does not contain water and is denoted as the brucite or C6-type structure. Another form of nickel hydroxide, known as the y-modification, can be prepared from concentrated KOH, leading to the incorporation of potassium ions into the lattice. The inclusion of K and other species as well can alter considerably the physicochemical properties of the otherwise pure... 

Lotmar and Feitknecht investigated variations in ionic distances of bivalent basic metal halogenides with layered structures of the Cdl2 type. In this context they needed the unit cell dimensions of nickel hydroxide as well as cobalt hydroxide. 

A series of mischmetal nickel alloys are known as typical hydrogen-absorbing materials (see Chapter 6.3) and are used as the negative electrode in Ni-MH rechargeable batteries (see Chapter 8.4). By the fluorination treatment of mischmetal nickel alloys the electric conductivity is significantly improved by the replacement of La-oxide and La-hydroxide layers on the Ni-emiched Lap2 surface. The layer was also found to protect the surface firom KOH alkaline solution as electrolyte and to improve the long-term durability. 

Cathodic electroprecipitation is a technique used commercially to prepare nickel hydroxide deposits in the battery field.25 In this case a nickel salt is present in solution at low pH (ca. 3.0) and hydrogen gas evolution around the cathode causes a local increase in pH, resulting in the precipitation of an adherent layer of nickel hydroxide at the metal surface. Similarly, anodic electroprecipitation is used commercially26 to produce layers of another highly active battery material, y-MnO2. 

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