Investigation Of Limiting Current Oxygen Sensors With Mic As Dense Diffusion Layer

Exhaust pollution from automobile is becoming worse and worse, while laws and regulations to control exhaust pollution are becoming more and more strict. Scientists research an oxygen sensor which controls and monitors the phenomenon of discharging poisonous gas by combining with 3-way catalysis system. Limiting current oxygen sensor receives much attention lately as it has fast response and high sensitive characteristics, and does not need any reference gas.Effect of Li2O additive on phase structure, density and electric properties of Ce0.8Gd0.2O1.9 were investigated, YST / CGO dual-phase composite Mixed Conductor (MIC) dense diffusion layer materials were prepared. Limiting current oxygen sensor using YSZ and CGO as electrolyte and LSC and YST / CGO as dense diffusion barrier were constructed by screen printing technique and co-pressing and co-sintering, respectively. The crystalline phase, microstructure and electrical conductivity of materials were investigated by XRD, SEM and EIS, respectively. Sensor's microstructures were analyzed by SEM. The relations between voltage and oxygen concentration of limiting current were investigated by dynamic scan.When doped with 3 mol% Li, the bulk density of CGO sintered at 1450℃was the same as that of pure CGO sintered at 1600℃, the sintering temperature reduced by150℃from 1600℃without aids. After adding 3 mol% Li, the major phase of the sample was fluorite structure for single-phase CGO when sintering at 1450℃, the average grain size was about 5μm , the electrical conductivity reached 100 (S.cm) at 800℃with the highest level, the activation energy was only 0.77eV.The bulk density of YST / CGO samples sintered at 1600℃was more than 90%. The two-phase of YST/CGO1 and YST/CGO2 had an obvious difference in color, the grain was clear. Sintered sample of each component was still single-phase structure for none reaction occurred. The electrical conductivity of the sample decreased with the proportion of YST increased. YST/CGO1 had the maximal electrical conductivity about 10-1 (S.cm), the activation energy was 1.01eV.The oxygen sensors, with YST/CGO1 and YST/CGO2 as diffusion layers, respectively, both got stable current plateaus in oxygen concentration from 300ppm to 800ppm when temperature was from 600~700℃and voltage was 0.5~1.1V. There was a excellent linear relationship between limiting current and oxygen concentration,and the correlation coefficient was above 0.99.Thick film LSC as dense diffusion layer based limiting current oxygen sensors prepared by screen printing technology on YSZ solid electrolyte. SEM results indicated that the LSC film thickness was about 30μm. The limiting current increased almost linearly with increased oxygen concentration in the range of 7000~105000ppm under 650~800℃. The sensor displayed a good oxygen sensitive performance.