The Research On The Structure And Material Of Sensing Electrode For YSZ-based Mixed Potential NO₂ Sensor

Based on this fact of increasingly severe NO_x pollution,legeslations and technologies have been introduced to restrict NO_x emissions worldwide.As the most widely used DeNO_x technology,Selective Catalytic Reduction?SCR?requires sensors to monitor NO_x concentrations in real-time.The mixed-potential NO_x sensor based on YSZ electrolyte has become a research hotspot with high sensitivity,good stability and simple structure.The main disadvantage of the potential type sensor is that the response to NO and NO₂ are opposite,which causes interference to the detection result.How to solve the NO/NO₂interference while ensuring high sensitivity to simplify the structure and process is a problem worth discussing.In the sensor,the sensing electrode?SE?plays an important role in gas adsorption and electrochemical reaction.The sensing characteristics of the sensor are determined by material and structure of the SE.The work attempts to solve the above problem from the structure optimization and material selection of sensing electrode.Firstly,sensors based on YSZ electrolyte and Co₃O₄ sensing material was prepared.By adjusting the sintering temperature and controlling the area and position of the Pt layer in sensing electrode,the effects of the micro-morphology and the macro-configuration of the sensing electrode on the sensor response were studied.The 700°C sintered sensor showed the maximum responses to NO₂ at 350-450°C.When the Pt layer was on the top of the Co₃O₄layer,the increase of the Pt area would result in a decrease in the overall catalytic performance of the electrode,thereby weakening the response.However,while the Pt layer was under the Co₃O₄ layer,the larger the Pt layer is,the more effective catalytic sites would be facilitated,contributing to the promotion in response.The sensor with sensing materials on a large Pt layer showed high response and good long-term stability and cycling stability.Subsequently,the paper selected the highly sensitive material,spinel NiFe₂O₄ to improve sensitivity and selectivity.The sensor based on YSZ electrolyte and NiFe₂O₄ sensitive electrode was prepared and tested.The sensor showed highest sensitibity to NO₂,up to 82.8mV/decade,at 450°C.Besides,it exhibited excellent cycling stability,but its anti-oxygen interference ability was rather poor,and selectivity need to be further improved.In addition,EIS was used to explain the sensitive mechanism of the sensor from the electrochemical point of view,indicating that the mixed potential response was related to the change of the electrolyte/electrode interface resistance caused by the electrochemical reaction.Mullite SmMn₂O₅ is a highly efficient NO oxidation catalyst.The paper attempts to use SmMn₂O₅ as sensing material to convert NO to NO₂ in order to solve the problem of mutual interference between them.The nano SmMn₂O₅ powder was synthesized by coprecipitation method derived by nonionic surfactant,followed by screen printing and sintering at 900°C to prepare the sensing electrode.The electrode exhibited responses to NO and NO₂ in the same direction,and high sensitivity,cycling stability and selectivity.The maximum sensitivity of NO and NO₂ is 83.23,124.45 mV/decade,respectively,which provides a solution to the problem of NO and NO₂ signal interference.