Nickel(II) hydroxide

Nickel(II) hydroxide is the inorganic compound with the formula Ni(OH)₂. It is a lime-green solid that dissolves with decomposition in ammonia and amines and is attacked by acids. It is electroactive, being converted to the Ni(III) oxy-hydroxide, leading to widespread applications in rechargeable batteries.^[6]

Nickel(II) hydroxide

Names
IUPAC name Nickel(II) hydroxide
Other names Nickel hydroxide, Theophrastite
Identifiers
CAS Number	12054-48-7 Y 36897-37-7 (monohydrate) N
3D model (JSmol)	Interactive image
ChemSpider	55452 Y
ECHA InfoCard	100.031.813
EC Number	235-008-5
PubChem CID	61534
RTECS number	QR648000
UNII	L8UW92NW6J Y
CompTox Dashboard (EPA)	DTXSID90274011
InChI InChI=1S/Ni.2H2O/h;2*1H2/q+2;;/p-2 Y Key: BFDHFSHZJLFAMC-UHFFFAOYSA-L Y InChI=1/Ni.2H2O/h;2*1H2/q+2;;/p-2 Key: BFDHFSHZJLFAMC-NUQVWONBAJ
SMILES [Ni+2].[OH-].[OH-]
Properties
Chemical formula	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)
Solubility in water	0.0015 g/L[1]
Solubility product (Ksp)	5.48×10−16[2]
Magnetic susceptibility (χ)	+4500.0·10−6 cm3/mol
Structure[3]
Crystal structure	hexagonal, hP3
Space group	P3m1, No. 164
Lattice constant	a = 0.3117 nm, b = 0.3117 nm, c = 0.4595 nm α = 90°, β = 90°, γ = 120°
Thermochemistry
Std molar entropy (S⦵298)	79 J·mol−1·K−1[4]
Std enthalpy of formation (ΔfH⦵298)	−538 kJ·mol−1[4]
Hazards
GHS labelling:[5]
Pictograms
Signal word	Danger
Hazard statements	H302, H315, H317, H332, H334, H341, H350, H360, H372
Precautionary statements	P201, P260, P280, P284, P405, P501
Lethal dose or concentration (LD, LC):
LD50 (median dose)	1515 mg/kg (oral, rat)
Safety data sheet (SDS)	External SDS
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). N verify (what is YN ?) Infobox references

The test tube in the middle contains a precipitate of nickel(II) hydroxide

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.^[7][8] The β form adopts a hexagonal close-packed structure of Ni²⁺ and OH⁻ ions.^[7][8] In the presence of water, the α polymorph typically recrystallizes to the β form.^[7][9] 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.^[7]

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.^[10] A nickel-magnesium variant of the mineral, (Ni,Mg)(OH)₂ had been previously discovered at Hagdale on the island of Unst in Scotland.^[11]

Reactions

Nickel(II) hydroxide is frequently used in electrical car batteries.^[8] 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).^[12][13]

Reaction 1 Ni(OH)₂ + OH⁻ → NiO(OH) + H₂O + e⁻

Reaction 2 M + H₂O + e⁻ → MH + OH⁻

Net Reaction (in H₂O) Ni(OH)₂ + M → NiOOH + MH

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.^[9]

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 Ni₃O₂(OH)₄.^[14]

Toxicity

The Ni²⁺ ion is a carcinogen when inhaled.

See also

• List of minerals named after people
• Nickel–cadmium battery
• Nickel–hydrogen battery
• Nickel–metal hydride battery
• Nickel–iron battery

References

1. CRC Handbook of Chemistry and Physics (84 ed.). CRC press. 2003. pp. 4–71. ISBN 0849304849.
2. John Rumble (June 18, 2018). CRC Handbook of Chemistry and Physics (99 ed.). CRC Press. pp. 5–189. ISBN 978-1138561632.
3. Enoki, Toshiaki; Tsujikawa, Ikuji (1975). "Magnetic Behaviours of a Random Magnet, Ni_pMg_(1-p)(OH₂)". Journal of the Physical Society of Japan. 39 (2): 317. Bibcode:1975JPSJ...39..317E. doi:10.1143/JPSJ.39.317.
4. Zumdahl, Steven S. (2009). Chemical Principles (6 ed.). Houghton Mifflin Company. p. A22. ISBN 978-0-618-94690-7.
5. "Nickel Hydroxide". American Elements. Retrieved 2018-08-30.
6. Chen, J.; Bradhurst, D.H.; Dou, S.X.; Liu, H.K. (1999). "Nickel Hydroxide as an Active Material for the Positive Electrode in Rechargeable Alkaline Batteries". Journal of the Electrochemical Society. 146 (10): 3606–3612. Bibcode:1999JElS..146.3606C. doi:10.1149/1.1392522. S2CID 33058220.
7. Oliva, P.; Leonardi, J.; Laurent, J.F. (1982). "Review of the structure and the electrochemistry of nickel hydroxides and oxy-hydroxides". Journal of Power Sources. 8 (2): 229–255. Bibcode:1982JPS.....8..229O. doi:10.1016/0378-7753(82)80057-8.
8. Jeevanandam, P.; Koltypin, Y.; Gedanken, A. (2001). "Synthesis of Nanosized α-Nickel Hydroxide by a Sonochemical Method". Nano Letters. 1 (5): 263–266. Bibcode:2001NanoL...1..263J. doi:10.1021/nl010003p.
9. Shukla, A.K.; Kumar, V.G.; Munichandriah, N. (1994). "Stabilized α-Ni(OH)₂ as Electrode Material for Alkaline Secondary Cells". Journal of the Electrochemical Society. 141 (11): 2956–2959. Bibcode:1994JElS..141.2956V. doi:10.1149/1.2059264.
10. Marcopoulos, T.; Economou, M. (1980). "Theophrastite, Ni(OH)₂, a new mineral from northern Greece" (PDF). American Mineralogist. 66: 1020–1021.
11. Livingston, A.; Bish, D. L. (1982). "On the new mineral theophrastite, a nickel hydroxide, from Unst, Shetland, Scotland" (PDF). Mineralogical Magazine. 46 (338): 1. Bibcode:1982MinM...46....1L. doi:10.1180/minmag.1982.046.338.01. S2CID 8381523.
12. Ovshinsky, S.R.; Fetcenko, M.A.; Ross, J. (1993). "A nickel metal hydride battery for electric vehicles". Science. 260 (5105): 176–181. Bibcode:1993Sci...260..176O. doi:10.1126/science.260.5105.176. PMID 17807176. S2CID 9523468.
13. Young, Kwo (2016). Nickel Metal Hydride Batteries. MDPI. doi:10.3390/books978-3-03842-303-4. ISBN 978-3-03842-303-4.
14. O. Glemser (1963). "Nickel (II) Hydroxide and Nickel (II,III) Hydroxide". In G. Brauer (ed.). Handbook of Preparative Inorganic Chemistry, 2nd Ed. Vol. 2. New York: Academic Press. p. 1549-1551.