Nickel(II) Oxide
Properties
| State | Solid |
| Color | Green (fine powder) to black (sintered) |
| Solubility | Insoluble in water; soluble in acids and ammonia |
| Melting Point | 1955 °C |
About Nickel(II) Oxide
Nickel(II) oxide is a deep-green-to-black solid (formula NiO, molar mass 74.692 g/mol) that crystallizes in the rock-salt structure — the same NaCl lattice you draw in freshman chem — with octahedral Ni²⁺ surrounded by six O²⁻ neighbors. It's also the textbook Mott insulator: simple band theory says the partially filled 3d band should make NiO a metal, but strong on-site Coulomb repulsion (the Hubbard U, around 8 eV here) splits the band into lower and upper Hubbard bands separated by roughly a 4 eV gap, so NiO is actually a wide-gap insulator. That correlation physics is why NiO shows up in every condensed-matter textbook. It's antiferromagnetic below a Néel temperature of 523 K — one of the highest among binary oxides — with the spins ordering in the [111] planes. Industrially, NiO is the gateway to most nickel-based battery cathodes: it's the precursor for LiNiO2 and the modern NMC family (LiNi1-x-yMnxCoyO2), where high-nickel formulations like NMC-811 deliver over 200 mAh/g and dominate EV battery packs from Tesla to BYD. NiO also serves as a steam-reforming catalyst for methane-to-syngas conversion, a green pigment in ceramic glazes, and a p-type hole-transport layer in perovskite solar cells.
Where you'll encounter it
If you've ever held a Tesla battery module or a Chevy Bolt cell in your hands, the cathode powder inside started its life as NiO — most commercial NMC and NCA syntheses begin with co-precipitating Ni(OH)2 from sulfate solution, calcining it to NiO under air, then lithiating with Li2CO3 at 750–900°C to grow the layered oxide cathode. In a materials-characterization lab, NiO is the standard antiferromagnetic reference for setting the exchange bias on spin-valve sensors — every hard-disk read head built between 1997 and roughly 2010 used a NiO or Ni-Mn pinning layer. In a high-school chemistry demonstration, finely divided NiO is the green dust that turns the kiln glaze on stoneware pots that color you see on rustic dinnerware comes from a few percent NiO in the glaze recipe.
Common Uses
- Cathode precursor for LiNiO2, NMC-811, and NCA lithium-ion battery materials in EV packs
- Positive electrode active material in nickel-cadmium and nickel-metal-hydride rechargeable batteries
- Industrial catalyst for steam reforming methane to syngas at 700-1000°C in fertilizer and methanol plants
- Hydrogenation catalyst for unsaturated fats in food processing and fine-chemical synthesis
- Green pigment in stoneware glazes and decorative ceramic enamels
- Hole-transport layer in inverted-architecture perovskite solar cells
- Reference antiferromagnet for exchange-bias setting in spin-valve magnetic sensors
Safety Information
GHS classifications: H351 (suspected carcinogen) and H372 (causes damage to organs through prolonged or repeated exposure - respiratory tract). IARC Group 1 carcinogen (nickel compounds, inhalation). OSHA PEL is 1 mg/m3 as Ni for insoluble nickel compounds (8-hour TWA); ACGIH TLV is 0.2 mg/m3. NiO is poorly absorbed when ingested but the inhalation hazard is serious — fine particles deposit deep in the lung and clear slowly. Strong skin sensitizer. Handle dust in a fume hood or with PAPR-grade respiratory protection; never dry-grind without ventilation. Calcination operations require local exhaust. Spent battery cathode containing NiO must be processed through licensed e-waste recyclers, not landfilled.
This safety summary is for educational reference only and may not be complete. It is not a substitute for Safety Data Sheets (SDS), medical advice, or professional chemical safety guidance. Always consult appropriate SDS and qualified professionals before handling chemicals.