A tubular flexible gas sensor fabricated by liquid-borne ultrasound for higher sensitivity and stability

Abstract

Further enhancement of sensitivity and stability of flexible gas sensors with a low cost will definitely widen their application range. In this work, a novel structure for flexible gas sensors is proposed and developed to significantly enhance the sensing performance, in which a sensing layer is coated on the inner wall of a flexible tube. To coat the sensing layer onto the inner wall, liquid-borne ultrasound is utilized, which not only makes the inner wall coating feasible at room temperature and normal pressure, but also has many green features such as low chemical reagent consumption. To the best of our knowledge, this is the first attempt to apply liquid-borne ultrasound in the coating process for flexible gas sensors. Tubular SnO2-rGO NH3 sensors fabricated by this method, have a measured LDL of 1 ppm, which is lower than the lowest one (5 ppm) of reported planar NH3 sensors with the same sensing material. The sensing response only decreases about 3.6 % for 1 ppm NH3 after 2000 loading-unloading cycles at 40 % strain and 0.5 Hz frequency. Apart from these merits, the inner wall sensing structure can protect the sensing layer from contaminants and touching. Thus, the flexible gas sensors developed in this work have very good mechanical stability.