Nickel(II) hydroxide

Nickel(II) hydroxide is the inorganic compound with the formula Ni(OH)2. It is an apple-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.[4]

Nickel(II) hydroxide
Names
IUPAC name
Nickel(II) hydroxide
Other names
Nickel hydroxide, Theophrastite
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.031.813
EC Number
  • 235-008-5
RTECS number
  • QR648000
UNII
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)
0.13 g/L
+4500.0·10−6 cm3/mol
Structure[1]
hexagonal, hP3
P3m1, No. 164
a = 0.3117 nm, b = 0.3117 nm, c = 0.4595 nm
α = 90°, β = 90°, γ = 120°
Thermochemistry
79 J·mol−1·K−1[2]
Std enthalpy of
formation (ΔfH⦵298)
 −538 kJ·mol−1[2]
Hazards
Safety data sheet External SDS
GHS pictograms [3]
GHS Signal word Danger[3]
GHS hazard statements
 H302, H332, H315, H334, H317, H341, H350, H360, H372[3]
P260, P284, P201, P280, P405, P501[3]
Lethal dose or concentration (LD, LC):
1515 mg/kg (oral, rat)
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.[5][6] The β form adopts a hexagonal close-packed structure of Ni2+ and OH− ions.[5][6] In the presence of water, the α polymorph typically recrystallizes to the β form.[5][7] 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.[5]

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.[8] A nickel-magnesium variant of the mineral, (Ni,Mg)(OH)2 had been previously discovered at Hagdale on the island of Unst in Scotland.[9]

Reactions

Nickel(II) hydroxide is frequently used in electrical car batteries.[6] 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).[10][11]

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.[7]

Synthesis

The synthesis entails treating aqueous solutions of nickel(II) salts with potassium hydroxide.[12]

Toxicity

The Ni2+ ion is a known carcinogen. 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.[4]

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See also
  • Nickel-cadmium battery
  • Nickel hydrogen battery
  • Nickel metal hydride battery
  • Nickel-iron battery

References
  1. Enoki, Toshiaki; Tsujikawa, Ikuji (1975). "Magnetic Behaviours of a Random Magnet, NipMg(1-p)(OH2)". Journal of the Physical Society of Japan. 39 (2): 317. doi:10.1143/JPSJ.39.317.
  2. Zumdahl, Steven S. (2009). Chemical Principles 6th Ed. Houghton Mifflin Company. p. A22. ISBN 978-0-618-94690-7.
  3. "Nickel Hydroxide". American Elements. Retrieved 2018-08-30.
  4. 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". J. Electrochem. Soc. 146 (10): 3606–3612. doi:10.1149/1.1392522.
  5. 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. doi:10.1016/0378-7753(82)80057-8.
  6. Jeevanandam, P.; Koltypin, Y.; Gedanken, A. (2001). "Synthesis of Nanosized α-Nickel Hydroxide by a Sonochemical Method". Nano Letters. 1 (5): 263–266. doi:10.1021/nl010003p.
  7. Shukla, A.K.; Kumar, V.G.; Munichandriah, N. (1994). "Stabilized α-Ni(OH)2 as Electrode Material for Alkaline Secondary Cells". J. Electrochem. Soc. 141 (11): 2956–2959. doi:10.1149/1.2059264.
  8. Marcopoulos, T.; Economou, M. (1980). "Theophrastite, Ni(OH)2, a new mineral from northern Greece" (PDF). American Mineralogist. 66: 1020–1021.
  9. Livingston, A.; Bish, D. L. (1982). "On the new mineral theophrastite, a nickel hydroxide, from Unst, Shetland, Scotland" (PDF). Mineralogical Magazine. 46 (338): 1. doi:10.1180/minmag.1982.046.338.01.
  10. Ovshinsky, S.R.; Fetcenko, M.A.; Ross, J. (1993). "A nickel metal hydride battery for electric vehicles". Science. 260 (5105): 176–181. doi:10.1126/science.260.5105.176. PMID 17807176.
  11. Young, Kwo (2016). Nickel Metal Hydride Batteries. MDPI. doi:10.3390/books978-3-03842-303-4. ISBN 978-3-03842-303-4.
  12. Glemser, O. (1963) "Nickel(II) Hydroxide" in ""Handbook of Preparative Inorganic Chemistry, 2nd ed. G. Brauer (ed.), Academic Press, NY. Vol. 1. p. 1549.
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