Improved response of H2S gas sensors with CuO nanoparticles on SnO2 film

In our earlier work enhanced H2S detection characteristics were observed in a novel sensor structure consisting of uniformly distributed CuO islands on SnO2 films. Ultra-thin CuO in the form of dotted islands on SnO2 film exhibited a high sensitivity (S = 7.3 x 10(3)) at a low operating temperature (150 degreesC), and a fast response speed of 14 s was obtained for H2S gas detection. In the initial study the CuO islands were large in diameter (0.6 mm) quite thick (10 rim) and were widely dispersed (1.2 mm apart). In the present work a systematic study on the catalyst CuO thickness and its distribution is reported and improved response and recovery are shown with chemically derived CuO nanoparticles. The main focus is towards trace-level (20 ppm) H2S gas detection and sensor response characteristics including sensitivity and response speed with varying distribution of CuO catalyst on SnO2 surface. The sensor operating temperature at which a maximum response is observed is found to decrease to a lower temperature of 130 degreesC with surface dispersed CuO nanoparticles. The response speed of the sensors to H2S gas becomes progressively faster when the CuO catalyst is dispersed as nanoparticles or as dotted islands onto the SnO2 film surface. With the SnO2-CuO-nano sensor, a high sensitivity of 2 x 10(3) at a low operating temperature of 130 degreesC is obtained with a fast response speed of 16 seconds for 20 ppm of H2S gas and a recovery time of 61 seconds is measured. Enhanced catalytic activity is observed due to the presence of CuO nanoparticles and their spatial distribution allows for, an effective removal of adsorbed oxygen from the uncovered SnO2 surface. Dissociated hydrogen available from the CuO-H2S interaction spills over and is found to be primarily responsible for the observed fast response characteristics.