A novel miniaturized oxygen sensor with solid-state ceria–zirconia reference

Development of a novel oxygen sensor with a solid-state reference is reported. Unlike conventional oxygen sensors used in monitoring exhaust gas emissions, in which one side of the sensor must be directly exposed to the air reference, the oxygen sensor presented here employs a solid solution of 25 mol% zirconia in ceria as the reference. The sensor consists of yttria-stabilized-zirconia (YSZ) electrolyte and ceria–zirconia reference layers with platinum coating as electrodes. Tests have been performed with two simulated gases mixture of (91.6% He, 8.4% CO) and (93.8% He, 6% CO, 0.2% C2H6) at operating temperatures of 300, 325, 350, 400 and 450 °C. For the He/CO gas mixture, a sharp transition occurs at the stoichiometric value. For the He/CO/C2H6 gas mixture, hysteresis was observed at temperatures 300 and 325 °C, while at higher temperatures a sharp step on the rich side (λ=0.92) was seen. Unlike conventional sensors, where the developed voltage varies between 1000 and 100 mV, the present sensor exhibits a sharp variation in the voltage, from 350 to −80 mV, an anomalous and interesting behavior not observed in air-referenced structures. The oxygen sensor can be miniaturized, yielding a low-cost sensor with a fast response, especially during cold start.