Amperometric NO₂Sensors Based On Lanthanum Silicates

The solid electrolyte type NO2sensors with fast response, high sensitivity and goodselectivity, especially excellent durability at elevated temperatures, have the widespreadprospect of application. The apatite-type lanthanum silicate is an excellent solidelectrolyte. The infuence of doping with metal cations at Si site on the properties ofLa10Si6O27was discussed. And the lanthanum silicates were used as electrolyte for theamperometric-type NO2sensors. The sensitive electrodes of nano-particles CuO andCuO/Ag were in situ prepared by wet chemical impregnation technology. The compositionand microstructure of the sensing electrodes were characterized by XRD, SEM and EDX,respectively. The sensing performances were also investigated.The lanthanum silicates of doping with various metal cations La10Si5MO27-δ(M=Al,Mg, Nb, Sn, Zr, W, Si) were synthesized via the high-temperature solid state process. Thetotal conductivity was improved when Al3+, Mg2+, Nb5+were doped at Si site. The bestconductivity was4.02×10-2S·cm-1at800oC on La10Si5AlO26.5. The total electricalconductivity of La10Si5MO27-δwas almost independent of oxygen partial pressure, whichindicated that the conduction ion was pure oxide-ion.An amperometric-type NO2sensor which is based on La10Si5NbO27.5electrolyte andnano-structured CuO sensing electrode was fabricated. The effects of different CuOloading on the sensing properties were also investigated. The sensor with7.8wt.%CuOloading exhibited best sensing performance. The response of current was almost linear toNO2concentration in the range of25~500ppm at600~800oC.An amperometric-type NO2sensor based on La10Si5AlO26.5electrolyte and nano-structured CuO/Ag sensing electrode was fabricated. With the Ag loading level increased,the sensitivity of the sensor increased remarkably and the best performance was observedat the CuO/Ag molar ratio of1:0.5. The sensor showed good response to NO2and theresponse of current was linear to NO2concentration at550~700oC. In additon sensors forO2, H2, CH4, CO2, NH3and acetone has good anti-interference ability.