- Cobalt(II) hydroxide, with the chemical formula Co(OH)₂, is an inorganic compound consisting of divalent cobalt ions (Co²⁺) coordinated with hydroxide ions (OH⁻).
- It typically appears as a pink to red or greenish solid, depending on the method of preparation and exposure to air. This compound is moderately stable under normal conditions but readily undergoes oxidation in the presence of oxygen or air, forming higher oxidation state cobalt compounds such as cobalt(III) hydroxide or cobalt(II,III) oxide (Co₃O₄).
- Cobalt(II) hydroxide can be synthesized through the precipitation reaction between a soluble cobalt(II) salt (like cobalt(II) sulfate or cobalt(II) chloride) and a strong base such as sodium hydroxide. The resulting precipitate is typically gelatinous and pink in freshly prepared form, but upon exposure to air, it tends to darken as it oxidizes, often turning green or black depending on the extent of oxidation and drying conditions.
- Chemically, Co(OH)₂ is sparingly soluble in water, making it a weak base. However, in acidic environments, it dissolves readily to form cobalt(II) salts, and under strongly alkaline conditions, it may form soluble cobaltate complexes. Its relatively low solubility and redox-active nature make it a useful intermediate in various chemical processes.
- Cobalt(II) hydroxide finds applications primarily in electrochemical and battery technologies. It is investigated as an active material for electrodes in rechargeable batteries, including nickel-cadmium (NiCd), nickel-metal hydride (NiMH), and alkaline secondary batteries. It also has potential in supercapacitors due to its favorable electrochemical properties. Its ability to undergo redox transitions between Co²⁺ and Co³⁺ during charge and discharge cycles makes it a candidate for energy storage systems.
- Additionally, Co(OH)₂ is used as a precursor in the production of cobalt oxides and other cobalt compounds. It may also be employed as a catalyst or catalyst support in various chemical reactions, particularly in oxidation or hydrogenation processes. In some cases, it is also explored for its potential in ceramics and pigment production, although it is less common in these roles than cobalt oxides.
- From a safety perspective, cobalt(II) hydroxide, like other cobalt compounds, must be handled with care. It may cause skin or respiratory irritation, and chronic exposure can pose systemic health risks, including possible carcinogenicity. Personal protective equipment (PPE) and proper laboratory practices are essential when working with this material.
