CoOx

CoOx is a general term for cobalt oxide materials with variable oxygen content and oxidation states. It encompasses well-defined stoichiometric oxides such as cobalt(II) oxide (CoO) and cobalt(II,III) oxide (Co3O4), as well as non-stoichiometric or defect-rich variants whose exact composition can deviate from ideal formulas. The term is common in catalysis and materials science to describe cobalt oxide phases whose properties are influenced by oxygen vacancies, surface hydroxyls, and mixed valence states.

In terms of structure, CoO crystallizes in a rock-salt lattice, while Co3O4 has a spinel structure with Co2+ occupying tetrahedral sites and Co3+ occupying octahedral sites. Non-stoichiometric CoOx often features defects and surface disorder that yield a range of cobalt oxidation states, typically between +2 and +3, contributing to changes in electronic structure and redox behavior.

Synthesis methods vary and include precipitation of cobalt salts followed by calcination in air or oxygen, as well as hydrothermal, solvothermal, and controlled reduction or oxidation processes. The processing atmosphere, temperature, and presence of supports or dopants determine the phase composition, particle size, and porosity, all of which influence catalytic and electrochemical performance.

Applications of CoOx materials span catalysis and energy storage. They are active in oxidation reactions, including CO and volatile organic compound oxidation, and serve as electrocatalysts for oxygen evolution and reduction in alkaline media. CoOx phases are also used as precursors to porous cobalt oxides and as components in battery and supercapacitor electrodes, where redox flexibility and conductivity are important. Characterization typically involves XRD for phase identification, XPS for oxidation states, electron microscopy for morphology, and surface-area analysis.