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 × 10³) at a low operating temperature (150°C), 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 nm) 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°C 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 × 10³ at a low operating temperature of 130°C is obtained with a fast response speed of 16 seconds for 20 ppm of HS 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.