Improved Toluene Response of Mixed-Potential Type YSZ-Based Gas Sensors Using CeO2-Added Au Electrodes

YSZ-based potentiometric sensors employing thin CeO 2 -added Au sensing electrodes (SEs) were fabricated by using a spin-coating method, and effects of the CeO 2 addition on their toluene sensing properties were examined. The sensor response (Δ E ) to 50 ppm toluene of the sensors using 8 wt% CeO 2 -added Au SEs tended to decrease with an increase in the number of spin-coating cycles ( x : 5, 10, 15; i.e., the thickness of SEs). However, Δ E of the sensors using 24 wt% CeO 2 -added Au SEs showed an opposite behavior to what was observed for 8 wt% CeO 2 -added Au SEs. The sensor using the thickest SE ( x : 15) showed the largest Δ E (e.g., ca. 212 mV for 50 ppm toluene) at 450 °C among all the sensors examined and responded even to 0.5 ppm toluene. Δ E exponentially increased with an increase in logarithmic toluene concentration in the range higher than 10 ppm. These obtained results indicate that electrochemical toluene oxidation proceeds at triple-phase boundaries in SE with gas (Au/CeO 2 /gas) in addition to conventional TPBs (SE/YSZ/gas) in addition to the conventional interface at SE/YSZ/gas, because CeO 2 is a mixed ionic and electronic conductor. The electrochemical reactions at TPBs of the sensor were also discussed on the basis of the I – E characteristics and the electrochemical impedance properties.