Nickel oxide Class of chemical compounds Nickel oxide may refer to: Nickel(II) oxide, NiO, green, well-characterised oxide Nickel(III) oxide, Ni2O3, black, not well-characterised oxide Nickel(IV) oxide Oxonickelates Index of chemical compounds with the same nameThis set index article lists chemical compounds articles associated with the same name.If an internal link led you here, you may wish to change the link to point directly to the intended article.