2NiOOH

2NiOOH is the chemical formula representing two units of nickel oxyhydroxide. Nickel oxyhydroxide (NiOOH) is a layered oxide–hydroxide that forms when nickel(II) hydroxide is oxidized in alkaline solutions. In practice NiOOH is described as NiOOH·xH2O and exists in α- and β- polymorphs, with nickel in the +3 oxidation state coordinated by octahedrally arranged oxygens and bridging hydroxide groups. The material is typically hydrous and can be crystalline or poorly crystalline, with its exact structure depending on synthesis conditions. NiOOH is commonly prepared by electrochemical oxidation of Ni(OH)2 in alkaline electrolytes or by chemical oxidation with strong oxidants.

In energy storage, NiOOH is the active positive electrode material in nickel-based rechargeable batteries. The redox couple NiOOH/Ni(OH)2 mediates charge transfer in alkaline solutions, described by NiOOH + H2O + e− ⇌ Ni(OH)2 + OH−. The material can exist as α- or β-NiOOH–type layers, and hydration influences conductivity and cycling stability. In discussions of reaction stoichiometry, 2NiOOH appears simply as two formula units of NiOOH and does not designate a distinct, separately characterized compound; it more often arises in balanced equations or theoretical considerations rather than as a separate solid with its own properties.

Safety: nickel oxyhydroxide and related nickel compounds require standard chemical hygiene; handling can pose risks of irritation and nickel exposure.