Investigation Of CeO₂-based Limiting Current Oxygen Sensor

Sm doped CeO2(Ce0.8Sm0.2O1.9, SDC) solid electrolyte, La0.8Sr0.2Co0.2Fe0.8O3-δ(LSCF),LaNi0.6Fe0.4O3-δ(LNF) using as dense diffusion barrier, and BaZr0.1Ce0.7Y0.1Yb0.1O3-δ(BZCYYb) as electron block respectively were prepared though the sol-gel method. Thephase compositions of which were characterized by X-ray power diffraction(XRD).A type of limiting current oxygen sensor with LSCF and LNF as diffusion layer,BZCYYb as electron block material, and SDC as solid electrolyte were fabricated byco-pressing and co-sintering and screen printing technique, respectively. Themicrostructures and the electrode interface resistance of the oxygen sensor wereinvestigated by the use of SEM and EIS respectively. The relations between voltage andoxygen concentration of limiting current oxygen sensor were investigated by dynamicscan.The result of XRD showed that SDC-carbonate composite electrolyte, which wasdoped with5wt%Li2CO3and Na2CO3(nLi:nNa=62:38), formed a sigle phase with cubicfluorite structure sintered at680℃. The sintering temperature of the SDC-carbonatecomposite electrolyte can be reduced about350℃so as to achieve co-pressing andco-sintering at1250℃for electrolyte and LNF barrier material.The oxygen sensor which fabricated by co-pressing and co-sintering, with LNF asdense diffusion layer and SDC as electrolyte material, both got stable current plateaus inoxygen concentration in3.51%-20%when temperature was in550℃-750℃. There was agood linear relationship between limiting current and oxygen concentration. The limitingcurrent increased with increasing temperature under condition of oxygen concentrationunchanged. The EIS showed that the resistance of solid electrolyte and oxygen sensordecreased with increasing temperature.The EIS of the oxygen sensor which fabricated by co-pressing and co-sintering withBZCYYb, SDC and LNF, showed that the resistance of oxygen sensor also decreased withincreasing temperature, and the value of resistance was bigger than the sensor’s without BZCYYb. The limiting current platform appeared in different oxygen concentrations whenvoltage was0.8V-1.7V and temperature was550℃-750℃. The current maximum valuereduced obviously after introducing of electron block material. The limiting currentlinearly increased with the oxygen volume fraction. In addition, the result of oxygensensitivity test indicated that the current maximun value decreased with the increasingthickness of electron block material, but the voltage platform interval became broaden.The thick film type oxygen sensor with LSCF as diffusion layer, also got stablecurrent plateaus in oxygen concentration from11%to20%at700℃. The currentmaximum value reached12mA, and as well as there was a linear relationship betweenlimiting current and oxygen concentration. The sensor displayed a good oxygen sensitiveperformance.