Nickel oxide is a green, crystalline solid, which is produced through the action of nickel and oxygen. It is used for a wide variety of applications, from colorant for stained glass, to enamel, to ceramics, to fuel cells. It is also a component of the secondary battery, and it is a precursor for many nickel salts.
NiO is non-graphitizable, and it is generally non-stoichiometric. The nickel:oxide ratio is often deviated from a value of one to one. Consequently, the oxidation rate of the solid is characterized by a large difference.
Depending on the type of single crystal, the oxide film can have different textures. This is a result of the presence of special grain boundaries. These grain boundaries are defined by the fact that they have misorientation axes that are close to the normal to the (100) plane. There are three types of grain boundaries: high-angle, low-angle, and arbitrary.
During the oxidation process, the nickel ions occupy the +2 oxidation state. Oxygen ions exist in the -2 oxidation state. In the +2 oxidation state, there are four nickel ions, one oxygen ion, and two nitrogen ions. Upon oxidation, the total positive charge on cations is equal to the total negative charge on anions.
Several investigations have been done to study the effect of foreign cations on nickel active materials. Some of these studies were performed in XPS. Using this technique, the oxidation state can be determined. XPS is useful for analyzing the chemical environment and for identifying functional groups.