Flexible resistive NO2 gas sensor of three-dimensional crumpled MXene Ti3C2Tx/ZnO spheres for room temperature application

MXene is a potential candidate of the sensing electrode for flexible gas sensing devices and has attracted considerable attention. However, two-dimensional (2D) MXene Ti3C2Tx nanosheet is liable to stack together and lose the high specific surface area, which limits its gas sensing performance. In this work, a room-temperature flexible NO2 sensor based on three-dimensional (3D) crumpled MXene sphere prepared by ultrasonic spray pyrolysis technology is developed. Then, the properties are further improved by designing 3D crumpled MXene sphere/ZnO composites sensitive electrode with high specific surface area and active sites. The selectivity of the flexible sensing device to NO2 is further highlighted, and the response signal to 100 ppm NO2 improves from 27.27 %-41.93 %, and the recovery characteristic substantially increases from similar to 30 % to similar to 100 %. The excellent NO2 sensing properties of 3D crumpled MXene sphere/ZnO are attributed to the high surface area, abundance of edges and defects caused by folding, and the formation of MXene/ZnO p-n heterojunction. This work has introduced an idea to improve MXene gas-sensing properties and helped us to further understand the sensing process between MXene and target gas.