Preparation and Performance of Pt/YSZ Pump Electrode for Amperometric NO_x Sensor
|School||Huazhong University of Science and Technology|
|Keywords||NO_X Sensor Amperometric Pt/YSZ Co-firing TPB ResponseCharacteristics|
NOX（Mainly includes NO and NO2） is the chief pollutant which leads to acid rainand photochemical smog. Most of NOXcomes from automobile exhaust. With theincreasing of consciousness for Environmental protection, various countries arere-enacted the strict automobile exhaust emission standards, and the regulation for NOXemissions has been stricter. Therefore, it is imperative to develop and optimize NOXsensor. Amperometric NOXsensor based on YSZ electrolyte is currently the onlycommercial product which limits to the low of measurement precision and slow ofresponse speed. Therefore, how to optimize its performance has become a researchhotspot.Using Pt, YSZ, glass material and metal oxide as raw materials, NOXsensor Pt/YSZelectrode slurries were fabricated. The effects of glass material on the co-firing matchingability of Pt/YSZ electrode and YSZ electrolyte were investigated. Oxygen pumpinglayer was prepared using YSZ as electrolyte and Pt/YSZ as electrode material. Theeffects of co-firing temperature and the YSZ addition amount on characteristic of Pt/YSZelectrode were analyzed in test gas of10vol%oxygen, while response characteristics ofPt/YSZ electrode were analyzed in different atmosphere.The effects of glass material on the co-firing matching ability of Pt/YSZ electrodeand YSZ electrolyte were analyzed. The results showed that it was beneficial to thecombination of Pt/YSZ electrode and YSZ electrolyte. The electrode which added glassmaterial was well combined with the YSZ electrolyte, however, the electrode which didnot add glass showed serious desquamate and stratification when co-firing with YSZelectrolyteThe effects of co-firing temperature on characteristic of Pt/YSZ electrode wereanalyzed. The results revealed that when the co-firing temperature increased, the pumpcurrent increased at first and then decreased, in contrast of the interface resistance. The electrode co-firing at1400℃had the longest of triple phase boundary and bestelectrode action; The activation energy of the electrode reactions on the Pt/YSZelectrodes decreased as the co-firing temperature increased.The effects of YSZ addition amount on characteristic of Pt/YSZ electrode wereanalyzed. The results revealed that the length of TPB increased at first and then decreasedwith the increase of the YSZ addition amount, in contrast of the interface resistance. Thelargest catalytic activity was achieved by adding20vol%YSZ into Pt slurry.Special attentions were paid on the response characteristics of pump oxygenelectrode on different atmosphere. The results showed that when the working temperaturewas fixed, the current density increased in a linear way with the increasing of the contentof rich-oxygen; The current density increased with the concentration of NO by index andthe base gas （10vol%O2） did not affect the response characteristic; The current densityincreased at first and then decreased when the reducing gases increased. The testingresults of the interface resistance were consistent with the pump current. When theconcentration of oxygen was fixed, pump current was an exponential function of workingtemperature and the concentration of oxygen did not affect the electrode activationenergy.