Room-temperature operable Cu-doped ZnO/TiO2 film gas sensor integrated with electrochromic visualization for NO detection

초록

In this study, a Cu-doped ZnO/TiO2 film capable of detecting NO gas at room temperature of 25 degrees C was fabricated using a dry deposition process, the nanoparticle deposition system (NPDS). Cu-doped ZnO nanopowders were synthesized via the wet impregnation method and mixed with TiO2 to improve their adhesion to the substrate. The fabricated Cu-doped ZnO/TiO2 film exhibited responses of 19.60 % to 240 ppm NO gas and 6.91 % to 10 ppm NO gas at 25 degrees C. Gas-sensing performances were compared with those of an undoped ZnO/TiO2 film. The Cu-doped ZnO/TiO2 film demonstrated 3.2 times higher response at 50 degrees C and 8.3 times higher response at 200 degrees C than the undoped film. Notably, while the undoped ZnO/TiO2 film did not respond at 25 degrees C, the Cu-doped ZnO/TiO2 film maintained stable sensing capability under the same conditions. These results indicate that Cu doping induces electron redistribution near oxygen vacancy sites in ZnO, enhancing reactivity at 50 degrees C and enabling NO gas ionization even at 25 degrees C, thus playing a critical role in ensuring stable operation at low temperatures. Furthermore, the room temperature-operable Cu-doped ZnO/TiO2 sensor was integrated with a viologen-based electrochromic device controlled by an Arduino, enabling a visual gas-sensing system that displayed real-time color changes in response to gas exposure. In conclusion, Cu-doped ZnO nanopowders synthesized via wet impregnation were successfully deposited onto substrates using NPDS. Cu doping was found to be essential at 25 degrees C operation and improved sensing reactivity.

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