CO sensor elements were fabricated by connecting two cerium oxide (ceria) thick films with and without Pt/alumina catalyst. The resistance of the thick films and the output voltage of the connected sensor elementwere investigated by changing the particle size of the cerium oxide thick films. The cerium oxide thick film sintered at 950 °C, which had a particle size of 50 nm, displayed better response for CO gas and lower resistance than those films sintered at 800 or 1000 °C. The resistance of the cerium oxide thick film sintered at 950 °C changed more quickly than those sintered at 800 or 1030 °C, when air including COwas introduced. The 90% response time of the cerium oxide thick film sintered at 950 °Cwas approximately 2 s. The connected sensor element with Pt/alumina catalyst fabricated in this study exhibited low response for combustible gases such as methane, ethane, propane, ethylene, and H2 at 450 °C, indicating that the connected sensor element has CO selectivity.
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