Nickel(II) hydroxide
Names | |
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IUPAC name
Nickel(II) Hydroxide | |
Other names
Nickel Hydroxide, Theophrasite | |
Identifiers | |
12054-48-7 36897-37-7 (monohydrate) | |
ChemSpider | 55452 |
EC number | 235-008-5 |
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Jmol-3D images | Image |
PubChem | 61534 |
RTECS number | QR648000 |
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Properties | |
Ni(OH)2 | |
Molar mass | 92.724 g/mol (anhydrous) 110.72 g/mol (monohydrate) |
Appearance | green crystals |
Density | 4.10 g/cm3 |
Melting point | 230 °C (446 °F; 503 K) (anhydrous, decomposes) |
0.013 g/100 mL | |
Solubility | soluble in dilute acid, ammonia (monohydrate) |
Structure | |
Crystal structure | hexagonal |
Thermochemistry | |
Std molar entropy (S |
79 J·mol−1·K−1[1] |
Std enthalpy of formation (ΔfH |
−538 kJ·mol−1[1] |
Hazards | |
LD50 (Median lethal dose) |
1515 mg/kg (oral, rat) |
Except where noted otherwise, data is given for materials in their standard state (at 25 °C (77 °F), 100 kPa) | |
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Infobox references | |
Nickel(II) hydroxide Ni(OH)2 is an insoluble compound with strong redox properties and widespread industrial and laboratory applications. It most commonly is used in rechargeable battery electrodes, by oxidation to nickel(III) oxide-hydroxide.[2]
Properties
Nickel(II) hydroxide has two well-characterized polymorphs, its α and β forms. The α structure consists of Ni(OH)2 layers with intercalated anions or water molecules occupying the space between layers.[3][4] The β form is a hexagonal closest-packed structure of Ni2+ and OH− ions, without other intercalated ions.[3][4] In the presence of water, the α polymorph typically decays to the β form due to dissolution and recrystalization.[3][5] 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.[3]
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.[6] A nickel-magnesium variant of the mineral, (Ni,Mg)(OH)2 had been previously discovered at Hagdale on the island of Unst in Scotland.[7]
Reactions
Ni(OH)2 readily undergoes oxidation to nickel oxyhydroxide, NiOOH, in combination with an reduction reaction, often of a metal hydride (reaction 1 and 2).[8]
Reaction 1 Ni(OH)2 + OH− → NiOOH + H2O + e−
Reaction 2 M + H2O + e− → MH + OH−
Net Reaction (in H2O) Ni(OH)2 + M → NiOOH + MH
Applications
Due to reactivity in redox processes nickel (II) hydroxide is frequently used in electrochemical cells. In particular, as a good capacitor, it is frequently used for the storage of electrochemical energy. For example, it has been proposed as a useful electrode for use in electrical car batteries.[4]
Of the two isomers, 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.[5]
Nickel hydroxides have also been proposed as materials for a variety of other purposes. These applications include a chromosomal DNA quantification assay.[9]
Synthesis
The earliest reported synthesis of nickel (II) hydroxide was described by Glemser and Einerhand, who used the oxidation of nickel nitrate with K2S2O8 and NaOH.[3]
A variety of alternative methods for the synthesis of nickel(II) hydroxide have been proposed to optimize its usefulness in a variety of applications. For example, to prevent the decay of the α to β polymorphy, Jeevandam et al. proposed a sonochemical synthesis technique that produced Ni(OH)2 ¬layers with substituted aluminum ions.[4] Fu et al. used an approach in which nickel foil was washed in acetone, dilute NaOH and HNO3 to form aqueous Ni(NO3)2•6H2O that was then collected through electrodeposition on a nickel foil electrode.[10]
Toxicity
The Ni2+ ion is a known carcinogen in both humans and mice, possibly by entry into cells via phagocytosis [8]. In the CHO cell line, Ni(OH)2, the LC50 dose has been shown to be 3.6 μg/ml. This high level of toxicity relative to other Ni2+ containing compounds is hypothesized to be due to the insoluble nature of the compound, and concentration in the nucleus.[11] Toxicity and related safety concerns have driven research into increasing the energy density of Ni(OH)2 electrodes, such as the addition of calcium or cobalt hydroxides.[2]
See also
- Nickel-cadmium battery
- Nickel hydrogen battery
- Nickel metal hydride battery
- Nickel-iron battery
External links
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References
- ↑ 1.0 1.1 Zumdahl, Steven S. (2009). Chemical Principles 6th Ed. Houghton Mifflin Company. p. A22. ISBN 0-618-94690-X.
- ↑ 2.0 2.1 Chen, J.; Bradhurst, D.H.; Dou, S.X.; Liu, H.K. J. Electrochem. Soc. 1999. 146, 3606-3612.
- ↑ 3.0 3.1 3.2 3.3 3.4 Oliva, P.; Leonardi, J.; Laurent, J.F. Journal of Power Sources. 1982, 8, 229-255.
- ↑ 4.0 4.1 4.2 4.3 Jeevanandam, P.; Koltypin, Y.; Gedanken, A. Am. Chem. Soc. Nano Letters. 2001, 1, 263-266.
- ↑ 5.0 5.1 Shukla, A.K.; Kumar, V.G.; Munichandriah, N. J. Electrochem. Soc.1994, 141, 2956-2959.
- ↑ Marcopoulos, T.; Economou, M. American Mineralogist, 1980, 66, 1020-1021.
- ↑ Livingston, A. and Bish, D. L. (March 1982) "On the new mineral theophrastite, a nickel hydroxide, from Unst, Shetland, Scotland". Mineralogical Magazine. 6 No. 338.
- ↑ Ovshinsky, S.R.; Fetcenko, M.A.; Ross, J. Science. 1993, 260, 176-181.
- ↑ Jiang, M.; Villagomez, R.; Vo, A.; Spears, L.G.; Electroanalysis. 2010, 23, 469-480.
- ↑ Fu, J.; Hu, Z.; Xie, L.; Jin, X.; Xie, Y.; Wang, Y.; Zhang, Z.; Yang, Y.; Wu, H. Int. J. Electrochem. Soc.2009, 4, 1052-1062.
- ↑ Fletcher, G.G.; Rossetto, F.E.; Turnbull, J.D.; Nieboer, E.Environmental Health Perspectives. 1994, 102, 69-74.