Polymer-based humidity sensor with fast response and multiple functions

Polymer-based films characterized by hydrophilic functional groups and porous structures are commonly utilized in humidity sensing due to their low-cost, non-toxic, and biodegradability. Despite advancements in polymer-based humidity sensors achieving rapid response time around 200 ms, many commonly used sensors still exhibit slower response time, often in the range of several seconds. Additionally, the absence of self-powered capabilities significantly restricts their practical applications. Here, we propose a humidity sensor based on a mixed cellulose ester (MCE) polymer film, featuring self-powering capability and high-power density. Notably, the sensor exhibits a response time of 80 ms, surpassing the currently reported state-of-the-art sensors with the response/recovery time of 150 ms, respectively. Furthermore, we demonstrate its applications in health monitoring and non-contact sensing for rapid detections of humidity changes associated with blinking, breathing, and finger interactions, highlighting the potential of next-generation humidity sensors.