NiOH2

Nickel(II) hydroxide, with the chemical formula Ni(OH)2, is an inorganic compound. It appears as a pale green solid and is practically insoluble in water. Nickel(II) hydroxide is a key component in the cathode of nickel-cadmium (NiCd) and nickel-metal hydride (NiMH) rechargeable batteries. In these batteries, it undergoes reversible electrochemical reactions, allowing for charge and discharge cycles.

The preparation of nickel(II) hydroxide typically involves the precipitation of nickel(II) salts with a base, such as sodium hydroxide. For instance, reacting nickel(II) sulfate with sodium hydroxide yields nickel(II) hydroxide and sodium sulfate. This precipitation process is often carried out in aqueous solutions.

Ni(OH)2 exists in different crystalline forms, including alpha and beta phases, which can influence its electrochemical properties. The alpha phase is generally more reactive and is often used in battery applications. The beta phase is more stable.

Beyond its prominent role in batteries, nickel(II) hydroxide is also used as a catalyst in certain chemical reactions. It can also be a precursor for the synthesis of other nickel compounds. Its properties make it a valuable material in various industrial and technological applications, particularly in energy storage.