Fast-response ionogel humidity sensor for real-time monitoring of breathing rate

Abstract

Ionogel-based chemoresistive humidity sensors have been successfully fabricated through ionothermal assembly of ionic liquids into a silica network. Our results demonstrated that ionogel sensors with different types of anions (Br⁻, BF₄⁻, and PF₆⁻) exhibited good humidity sensitivity, low humidity hysteresis, and good reproducibility. In particular, the response and recovery times of the SiO₂/[Bmim]Br-based sensor reached 3 s and 10 s, respectively, which were considerably shorter than those of other SiO₂-based humidity sensors. The improved sensitivity characteristics of SiO₂/[Bmim]Br can be attributed to its high conductivity and hydrophilicity, resulting in fast ion transfer using Br⁻ and H₃O⁺ as charge carriers under humid conditions. Furthermore, this ionogel sensor showed fast and substantial changes in impedance with changing humidity for real-time monitoring of human breath. These findings are expected to provide opportunities for the design and fabrication of high-performance sensors for online humidity monitoring.