CoOOH

CoOOH, also written cobalt oxyhydroxide, is a compound with the formula CoOOH. In many contexts it is described as cobalt(III) oxyhydroxide, a cobalt oxide–hydroxide species that forms under oxidizing conditions in basic media. It occurs as a pale brown solid and is often generated as an active phase in cobalt-based electrocatalysts.

Structure: CoOOH is related to layered transition metal oxyhydroxides. It consists of edge- and corner-sharing CoO6 octahedra arranged in sheets, with oxide and hydroxide groups linking the layers. The material can exist in multiple polymorphs, commonly labeled alpha-CoOOH and beta-CoOOH, with differences in interlayer spacing and water content. The presence of interlayer anions or water molecules can influence its conductivity and catalytic properties.

Preparation: CoOOH is typically prepared by electrochemical oxidation of Co(OH)2 or cobalt oxide precursors in alkaline solutions, which converts Co2+ to Co3+ and introduces oxide/hydroxide groups. It can also be synthesized via hydrothermal or chemical routes followed by oxidation.

Applications: A major use is as an active catalyst for the oxygen evolution reaction (OER) in alkaline water electrolysis. CoOOH and its hydrated derivatives are among cobalt-based electrocatalysts that operate in basic media. It also appears as an electrochemically active phase in rechargeable alkaline batteries and supercapacitors, and under redox cycling it can interconvert with other cobalt oxide/hydroxide phases.

Properties and safety: CoOOH is relatively insoluble in water and stable under alkaline conditions, but can transform to Co3O4 or Co(OH)3 under certain temperatures or reducing conditions. Cobalt compounds pose health and environmental hazards; appropriate handling and disposal are required.