Nanowire-Assembled Hierarchical ZnCo2O4 Microstructure Integrated with a Low-Power Microheater for Highly Sensitive Formaldehyde Detection.

Nanowire-assembled 3D hierarchical ZnCo2O4 microstructure is synthesized by a facile hydrothermal route and a subsequent annealing process. In comparison to simple nanowires, the resulting dandelion-like structure yields more open spaces between nanowires, which allow for better gas diffusion and provide more active sites for gas adsorption while maintaining good electrical conductivity. The hierarchical ZnCo2O4 microstructure is integrated on a low-power microheater platform without using binders or conductive additives. The hierarchical structure of the ZnCo2O4 sensing material provides reliable electrical connection across the sensing electrodes. The resulting sensor exhibits an ultralow detection limit of 3 ppb toward formaldehyde with fast response and recovery as well as good selectivity to CO, H2, and hydrocarbons such as n-pentane, propane, and CH4. The sensor only consumes ∼5.7 mW for continuous operation at 300 °C with good long-term stability. The excellent sensing performance of this hierarchical structure based sensor suggests the advantages of combining such structures with microfabricated heaters for practical low-power sensing applications.