A PLANAR-TYPE SENSOR FOR DETECTION OF OXIDIZING AND REDUCING GASES

A wide-range air-to-fuel (A/F) ratio sensor has been constructed with a planar structure using a single yttria-stabilized-zirconia (YSZ) electrolyte layer shared by electrochemical oxygen storage, pumping, and reference cells. The plasma-spray method is used to deposit porous YSZ electrolyte on sputtered Pt electrodes. The sensor is tested in a controlled test gas containing oxygen, carbon monoxide, and nitrogen and in propane burner exhaust gas. The limiting current of the sensor can be used to determine the A/F ratio in both lean and rich mixtures. The characteristic current versus voltage behavior of the wide-range A/F ratio sensor is elucidated by an analytical model describing the sensor operation. The sensor can also be used to measure the concentrations of H2O vapor and CO2, because the decomposition of these gases produces a second gas-diffusion-limited region. Because NO decomposes at a similar voltage to oxygen, it is necessary to measure the oxygen concentration independently to operate as a NO sensor.