Ultra‐Sensitive and High‐Resolution Flexible Iontronic Humidity Sensor for Detecting Subtle Moisture Differences

Abstract Artificial skins are a class of flexible devices designed to mimic the functionalities of human skins, primarily for detecting physical stimuli, including pressure, temperature, and strain. However, the lack of specialized humidity receptors in the human skin has led to the overlooked role of humidity perception, despite its importance in human tactile perception. This study reports an iontronic humidity sensor that achieves exceptional sensitivity and an ultrahigh resolution of 0.01% relative humidity (RH), enabled by a porous structure of the material and iontronic sensing mechanism. Compared with the Grotthuss proton transport mechanism commonly employed in humidity sensing, the proposed sensor achieves sensitivity two orders of magnitude higher than previously reported results. Furthermore, when other humidity sensor presents long response‐recovery times from a few seconds to hundreds of seconds, our sensor exhibits short response and recovery times of 0.9 and 0.5 s, respectively. The sensor can be integrated in a ring and to detect minute humidity variations, enabling the differentiation of moisture on twenty different fabrics. This humidity sensor might be used in advanced wearable devices and the integration of precise humidity sensing capabilities in robotics.