Increasing gas sensitivity of Co 3 O 4 octahedra by tuning Co-Co 3 O 4 (111) surface structure and sensing mechanism of 3-coordinated Co atom as an active center

Co 3 O 4 octahedrons enclosed by {111} facets were synthesized using Cl − ions as a crystal facet control agent. The Co 3 O 4 octahedrons show higher responses than Co 3 O 4 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–Co 3 O 4 (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 O 2 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.