Hydrogel‐Based Self‐Powered, Oxygen‐Resistant, and Flexible Sensors for Ultrasensitive and Selective NO ₂ Detection

Abstract Flexible nitrogen dioxide (NO 2 ) sensors hold great promise for timely protection of both the environment and human health. However, current NO 2 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 NO 2 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 NO 2 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 NO 2 . The superior NO 2 sensing performance of the sensor is synergistically attributed to the catalysis of the NO 2 reduction reaction by the employed Ag electrodes and the inhibition of NO 2 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 NO 2 leaks are implemented in both aerobic and anaerobic environments by connecting the developed sensor to a self‐designed wireless sensing system.