Adsorption of oxygen on high area nickel oxide. Part 1.—Structure and properties of the oxide

Abstract

Nickel oxide with a area of approximately 100 m² g^–1 has been prepared by low temperature decomposition of Ni(OH)₂. Under vacuum, it is yellow-green in colour but blackens on exposure to oxygen at room temperature with no measurable change in surface area. This colour change can be reversed by heating in vacuum at 200°C. The density of the black oxide is 6.0±0.3 Mg m^–3, more than 10 % less than that for bulk low area oxide. The oxide is still paramagnetic at 77 K and this suggests a particle size of less than 80 Å. Electron microscopy and diffraction establish that the oxide consists of very thin (20 Å in some cases) flakes that have the overall morphology of the parent hydroxide platelets (maximum width between 200 and 2 000 Å) and an orientation of (111) planes parallel to the surface. The flakes contain many irregularly shaped channels about 20 Å apart which separate domains of oxide generally without misorientation across the channel.