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Nickel(II) hydroxide is the
inorganic compound An inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds⁠that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as ''inorganic chemistry''. Inorgan ...
with the formula Ni(OH)2. It is a lime-green solid that dissolves with decomposition in
ammonia Ammonia is an inorganic chemical compound of nitrogen and hydrogen with the chemical formula, formula . A Binary compounds of hydrogen, stable binary hydride and the simplest pnictogen hydride, ammonia is a colourless gas with a distinctive pu ...
and
amines In chemistry, amines (, ) are organic compounds that contain carbon-nitrogen bonds. Amines are formed when one or more hydrogen atoms in ammonia are replaced by alkyl or aryl groups. The nitrogen atom in an amine possesses a lone pair of elec ...
and is attacked by acids. It is electroactive, being converted to the Ni(III) oxy-hydroxide, leading to widespread applications in
rechargeable batteries A rechargeable battery, storage battery, or secondary cell (formally a type of energy accumulator), is a type of electrical battery which can be charged, discharged into a load, and recharged many times, as opposed to a disposable or prima ...
.


Properties

Nickel(II) hydroxide has two well-characterized polymorphs, α and β. The α structure consists of Ni(OH)2 layers with intercalated anions or water. The β form adopts a hexagonal close-packed structure of Ni2+ and OH− ions. In the presence of water, the α polymorph typically recrystallizes to the β form. In addition to the α and β polymorphs, several γ nickel hydroxides have been described, distinguished by crystal structures with much larger inter-sheet distances. The mineral form of Ni(OH)2, theophrastite, was first identified in the Vermion region of northern Greece, in 1980. It is found naturally as a translucent emerald-green crystal formed in thin sheets near the boundaries of idocrase or chlorite crystals. A nickel-magnesium variant of the mineral, had been previously discovered at Hagdale on the island of
Unst Unst (; ) is one of the North Isles of the Shetland Islands, Scotland. It is the northernmost of the inhabited British Isles and is the third-largest island in Shetland after Shetland Mainland, Mainland and Yell (island), Yell. It has an area o ...
in Scotland.


Reactions

Nickel(II) hydroxide is frequently used in electrical car batteries. Specifically, Ni(OH)2 readily oxidizes to nickel oxyhydroxide, NiOOH, in combination with a reduction reaction, often of a metal hydride (reaction 1 and 2). Reaction 1 Reaction 2 Net Reaction (in H2O) Of the two polymorphs, α-Ni(OH)2 has a higher theoretical capacity and thus is generally considered to be preferable in electrochemical applications. However, it transforms to β-Ni(OH)2 in alkaline solutions, leading to many investigations into the possibility of stabilized α-Ni(OH)2 electrodes for industrial applications.


Synthesis

The synthesis entails treating aqueous solutions of nickel(II) salts with potassium hydroxide. When the same reaction is conducted in the presence of bromine, the product is .


Toxicity

The Ni2+ ion is a carcinogen when inhaled.


See also

*
List of minerals named after people This is a list of minerals named after people. The chemical composition of the mineral follows the name. A * Abelsonite: – American physicist Philip Hauge Abelson (1913–2004) * Abswurmbachite: – German mineralogist Irmgard Abs-Wurmbac ...
*
Nickel–cadmium battery The nickel–cadmium battery (Ni–Cd battery or NiCad battery) is a type of rechargeable battery using nickel oxide hydroxide and metallic cadmium as electrodes. The abbreviation ''Ni–Cd'' is derived from the chemical symbols of nickel (Ni) an ...
*
Nickel–hydrogen battery A nickel–hydrogen battery (NiH2 or Ni–H2) is a rechargeable electrochemical power source based on nickel and hydrogen. It differs from a nickel–metal hydride (NiMH) battery by the use of hydrogen in gaseous form, stored in a pressurized ...
*
Nickel–metal hydride battery A nickel–metal hydride battery (NiMH or Ni–MH) is a type of rechargeable battery. The chemical reaction at the positive electrode is similar to that of the nickel–cadmium cell (NiCd), with both using nickel oxide hydroxide (NiOOH). Ho ...
*
Nickel–iron battery The nickel–iron battery (NiFe battery) is a rechargeable battery having nickel(III) oxide-hydroxide positive plates and iron negative plates, with an electrolyte of potassium hydroxide. The active materials are held in nickel-plated steel tu ...


References

{{Hydroxides Nickel compounds Hydroxides