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 (Co3c) with one dangling bond at Co–Co3O4 (111) plane by eliminating surface Cl− ions and OH groups. Accordingly, we deem that the Co3c atom at (111) plane acts as an active center for sensing reaction and present an atomic and molecular level sensing mechanism. The Co3c 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 Co3c 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.