High operating temperature and low response restrict the application of H2S sensors. Due to the strong chemical affinity of CuO to H2S and the large band gap and high stability of β-In2S3, CuO nanotube/In2S3 nanosheet p/n heterostructures have been delicately designed for binder-free gas sensors by a facile method consisting of sputtering, chemical etching, and annealing. A switching effect of H2S concentration on the response of CuO/In2S3 gas sensors has been observed. When exposed to low-concentration H2S (1-10 ppm), the response is less than 0.10 and dominated by the surface-type adsorption-desorption process between CuO and H2S. When exposed to high-concentration H2S, the sensor exhibits a superior response of 3511 toward 50 ppm H2S, considerable selectivity, and long-term stability at room temperature. This dramatically enhanced response can be explained by the transformed junction from the CuO/In2S3 heterojunction to the CuS/In2S3 Schottky junction. These results suggest that the binder-free ceramic tube-type CuO/In2S3 gas sensor with considerable performance will have promising potential for H2S gas detection. Moreover, this method provides an effective strategy to fabricate other binder-free gas sensors.
Keywords: CuO nanotube; Schottky barrier; gas sensor; heterojunction; indium sulfide nanosheet; switching effect.