High-Performance Humidity Sensor Based on Ion–Electron Synergistic Composite Gel

Accurate humidity monitoring is crucial in numerous application fields, and developing humidity sensors that combine high sensitivity, fast response, wide-range detection, and long-term stability is of great significance. This work constructs a composite gel humidity-sensitive material (SCR&Br) with a semi-interpenetrating conductive network by introducing cellulose nanocrystals/reduced graphene oxide (CNCs/rGO) nanohybrid material with 1-ethyl-3-methylimidazolium bromide (EMIMBr) into a sodium alginate (SA) matrix. Based on the synergistic effect of organic and inorganic components, the material synergizes the porous hydrophilic characteristics of the organic phase with the electronic/ionic conductivity of the inorganic component to construct a gel-based sensing network for ion–electron cooperative transport. Further adopting the electrohydrodynamic (EHD) printing method to achieve controlled molding of the moisture-sensitive coatings, combined with the freeze-drying process, the porous SCR&Br humidity sensor was fabricated. By adjusting the proportions of each component, the fabricated SCR&Br sensor exhibits low humidity hysteresis (≤4.6%), fast response (∼6 s), and speed recovery (∼48 s), as well as good long-term stability (≥67 days) within the 11–95% relative humidity (RH) range. Such sensors are scalable and suitable for daily environmental humidity detection, indicating that high-performance humidity sensors based on low-cost organic–inorganic composite materials are emerging as effective candidates for environmental monitoring technologies.