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

Abstract

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.