Increasing gas sensitivity of Co3O4 octahedra by tuning Co-Co3O4 (111) surface structure and sensing mechanism of 3-coordinated Co atom as an active center.

Co₃O₄ octahedrons enclosed by {111} facets were synthesized using Cl⁻ ions as a crystal facet control agent. The Co₃O₄ octahedrons show higher responses than Co₃O₄ commercial particles to ethanol, methanol, acetone and triethylamine, and the responses are further enhanced by increasing the numbers of 3-coordinated Co atoms (Co_3c) with one dangling bond at Co–Co₃O₄ (111) plane by eliminating surface Cl⁻ ions and OH groups. Accordingly, we deem that the Co_3c atom at (111) plane acts as an active center for sensing reaction and present an atomic and molecular level sensing mechanism. The Co_3c atoms can produce free electrons, absorb O₂ molecules and catalyze the gas-sensing reactions. The surface engineering may be used to bolster gas-sensing properties of other metallic oxides. The concept of Co_3c atom as an active center will contribute to understand the true nature of the gas sensing and provide guidance on designing highly performance sensing materials. [ABSTRACT FROM AUTHOR]