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) ele ctrolyte 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 con trolled 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 senso r operation. The sensor can also be used to measure the concentrations of H2O vapor and CO2, because the decomposition of these gases produc es a second gas-diffusion-limited region. Because NO decomposes at a s imilar voltage to oxygen, it is necessary to measure the oxygen concen tration independently to operate as a NO sensor.