Impact of Relative Humidity on the Response of Hollow Tin Dioxide Microsphere-Based Impedimetric Sensors

A primary obstacle to the widespread application of impedimetric gas sensors is their susceptibility to environmental factors, particularly humidity, which severely limits their performance and reliability at room temperature. In this study, hollow tin dioxide (SnO₂) microspheres were synthesized using a silica-templating method and systematically evaluated as room-temperature humidity sensors. The frequency-dependent response of the hollow SnO₂ sphere-based sensors was first investigated from 0.1 Hz to 200 kHz across a 0-82% relative humidity (RH) range, which identified optimal performance in the low-frequency region (0.1-10 Hz). Based on this finding, a detailed characterization was conducted at 10 Hz. At this frequency, the sensors demonstrated a sensitivity of 7.1 × 10^-2 dec·(%RH^-1), a limit of detection (LoD) of 17%, response/recovery times of 50/120 s, and R ² = 0.99 for the log-linear model. The performance of hollow SnO₂ is attributed to a combination of the porous morphology with accessible inner and outer surface active sites and the favorable tetragonal rutile crystal phase. A dual sensing mechanism is proposed, governed by electronic effects from the surface adsorption of analyte gas molecules at low humidity and transitioning to being dominated by ionic conduction via the Grotthuss mechanism in physisorbed water layers at high humidity.