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). Occupational exposure limits for insoluble nickel compounds are expressed as elemental Ni and are set very low. 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. We deliberately do not publish occupational exposure limits or other regulatory thresholds: those values are revised over time and differ between jurisdictions, so the only correct source is the current SDS and the regulations that apply where you work.