Co3O4 sensors with a nanoscale TiO2 or SnO2 catalytic overlayer were prepared by screen-printing of Co3O4 yolk-shell spheres and subsequent e-beam evaporation of TiO2 and SnO2. The Co3O4 sensors with 5 nm thick TiO2 and SnO2 overlayers showed high responses (resistance ratios) to 5 ppm xylene (14.5 and 28.8) and toluene (11.7 and 16.2) at 250 °C with negligible responses to interference gases such as ethanol, HCHO, CO, and benzene. In contrast, the pure Co3O4 sensor did not show remarkable selectivity toward any specific gas. The response and selectivity to methylbenzenes and ethanol could be systematically controlled by selecting the catalytic overlayer material, varying the overlayer thickness, and tuning the sensing temperature. The significant enhancement of the selectivity for xylene and toluene was attributed to the reforming of less reactive methylbenzenes into more reactive and smaller species and oxidative filtering of other interference gases, including ubiquitous ethanol. The concurrent control of the gas reforming and oxidative filtering processes using a nanoscale overlayer of catalytic oxides provides a new, general, and powerful tool for designing highly selective and sensitive oxide semiconductor gas sensors.
Bibliographical noteFunding Information:
This work is supported by the Deanship of Scientific Research (DSR), King Abdulaziz University (KAU), under grant No. 2-135-36-HiCi, a National Research Foundation of Korea (NRF) grant funded by the Korea Government (MEST) (No. 2016R1A2A1A05005331), and Development of intelligent ceramic electrode/catalyst for Pt reducing in exhaust gas sensor by nonstoichiometric oxide material (No. 10062222) funded by Korea Government (MOTIE). The authors, therefore, acknowledge the technical and financial support of KAU, MEST, and MOTIE.
© 2017 American Chemical Society.
- catalytic overlayer
- gas filtering
- gas reforming
- gas selectivity
- gas sensor
ASJC Scopus subject areas
- General Materials Science