A Stable and Fast-Response Multifunctional Humidity Sensor Based on a Polyanionic Liquid Containing Bromide Ions

Humidity sensors are widely utilized in meteorological research, industrial production, precision instrument maintenance, agriculture, health care, and other fields. However, the long response time and low sensitivity of current metal oxide and hybrid humidity sensors limit their practical applications. In this study, a humidity sensor was prepared using a simple drop-casting method with 2-hydroxy-2-methylpropiophenone (HOMPP) and 1-vinyl-3-butylimidazolium bromide (C9H15BrN2) as the humidity sensing materials. This approach offers advantages such as low cost, high chemisorption capacity, and excellent moisture-sensitive performance. The prepared humidity sensors demonstrate high sensitivity, good repeatability, excellent flexibility, low hysteresis, and response/recovery times of 6/12.5 s, respectively, over a wide relative humidity (RH) range (2–97%). Additionally, the sensor exhibits potential for various multifunctional applications, including humidity detection in daily life, respiratory monitoring, non-contact sensing, and flexible electronics applications.