Hydrogel-Based Self-Powered, Oxygen-Resistant, and Flexible Sensors for Ultrasensitive and Selective NO₂ Detection

Flexible nitrogen dioxide (NO₂) sensors hold great promise for timely protection of both the environment and human health. However, current NO₂ sensing technologies face the dilemma of substantial power consumption, susceptibility to oxygen interference, and insufficient wearing comfort, seriously hindering their practical applications. Herein, a self-powered, oxygen-resistant, and flexible NO₂ sensor with a cell structure is proposed based on dense polyacrylamide-calcium alginate hydrogel network and a heterogeneous metal electrode pair with similar electrode potentials. The resulting NO₂ sensor exhibits an ultrahigh sensitivity of 307.17% per ppm, an ultra-low detection limit of 2.86 ppb, and high selectivity relative to the strongest interfering gas (oxygen), originating from the tiny electromotive force provided by this self-powered sensor exclusively driving the reduction of NO₂. The superior NO₂ sensing performance of the sensor is synergistically attributed to the catalysis of the NO₂ reduction reaction by the employed Ag electrodes and the inhibition of NO₂ solubilization by the dense hydrogel networks. The incorporation of glycerol into the hydrogel further enhances the environmental tolerance and stability of the device. Thanks to these, remote and real-time alarms for trace NO₂ leaks are implemented in both aerobic and anaerobic environments by connecting the developed sensor to a self-designed wireless sensing system.