Overview

Cobalt(II,III) oxide is a stable inorganic compound with the empirical formula Co3O4. It is a mixed‑valence oxide that contains both Co2+ and Co3+ species in a single lattice and commonly appears as a black or dark brown crystalline powder. For basic reference information see this source.

Structure and physical properties

Co3O4 adopts the normal spinel crystal structure: divalent cobalt ions occupy tetrahedral sites while trivalent cobalt ions occupy octahedral sites in an oxide framework. The material is insoluble in water but reacts with mineral acids to give soluble cobalt salts. It is electrically semiconducting and shows magnetic behavior characteristic of mixed‑valence transition metal oxides; further technical details are available at more details.

Synthesis and chemical behavior

The oxide can be prepared by controlled oxidation of cobalt(II) compounds or by thermal treatment of cobalt hydroxides in air. On heating or under reducing conditions it can be converted to other cobalt oxides such as CoO. Chemically it participates in redox reactions and serves as a precursor to many cobalt coordination compounds; synthesis notes are summarized at synthesis reference.

Uses and applications

  • Catalysis: employed in oxidation and oxygen‑evolution research and as a heterogeneous catalyst support.
  • Energy materials: studied for lithium‑ion or sodium‑ion battery anodes and supercapacitor electrodes.
  • Sensors and magnetic materials: used in gas sensing layers and in magnetic devices.
  • Pigments and precursors: a feedstock for other cobalt compounds and traditional ceramic colorants.

Applied examples and patents can be consulted via technical summaries such as application overview.

History, occurrence and safety

Cobalt minerals and oxides have been used historically to color glass and ceramics; Co3O4 is one of the common oxide forms encountered in laboratory and industrial settings. Like other cobalt compounds, specimens should be handled with care: dusts and soluble salts can be harmful if inhaled or ingested and appropriate protective measures are recommended. Regulatory and safety guidance can be found at safety information.