Self-healable, recyclable, ultrastretchable, and high-performance NO₂ sensors based on an organohydrogel for room and sub-zero temperature and wireless operation

To date, development of high-performance, stretchable gas sensors operating at and below room temperature (RT) remains a challenge in terms of traditional sensing materials. Herein, we report on a high-performance NO₂ gas sensor based on a self-healable, recyclable, ultrastretchable, and stable polyvinyl alcohol–cellulose nanofibril double-network organohydrogel, which features ultrahigh sensitivity (372%/ppm), low limit of detection (2.23 ppb), relatively fast response and recovery time (41/144 s for 250 ppb NO₂), good selectivity against interfering gases (NH₃, CO₂, ethanol, and acetone), excellent reversibility, repeatability, and long-term stability at RT or even at −20°C. In particular, this sensor shows outstanding stability against large deformations and mechanical damages so that it works normally after rapid self-healing or remolding after undergoing mechanical damage without significant performance degradation, which has major advantages compared to state-of-the-art gas sensors. The high NO₂ sensitivity and selectivity are attributed to the selective redox reactions at the three-phase interface of gas, gel, and electrode, which is even boosted by applying tensile strain. With a specific electrical circuit design, a wireless NO₂ alarm system based on this sensor is created to enable continuous, real-time, and wireless NO₂ detection to avoid the risk of exposure to NO₂ higher than threshold concentrations.