Impedance-metric Pt/YSZ/Au–Ga2O3 sensor for CO detection at high temperature

An electrochemical Pt/YSZ/Au–Ga2O3 sensor cell with the sensing electrode of Au-doped Ga2O3 has been fabricated to detect carbon monoxide at high temperature. It has been found that the electrochemical impedance spectroscopy is a sensitive technique for quantitative characterization of the response of the yttria-stabilized zirconia (YSZ) electrolyte sensor to CO gas. The total impedance of the sensor cell arises from the combined contribution of the Ohmic contact resistance, the electrolyte impedance and the interfacial impedance between the electrolyte and the sensing electrode. Only the interfacial impedance is sensitive to the presence of the CO gas, which is induced by an electrochemical oxidation of CO. Our experiments demonstrate that the impedance could be used as a sensing signal. The impedance value at 0.42 Hz is strongly dependent upon the CO concentration from 100 to 800 ppm at 550 °C. And the 90% response and 90% recovery time to 800 ppm CO were around 10 s.