The Research On Mn/Zn_xCo_1-xFe₂O₄ Sensing Materials For YSZ-Based Potentiometric NH₃ Sensors

There's a variety of poisonous and harmful gases in the automobile exhaust,NO _x?NO_x,NO and NO₂?are the most harmful gases among them.The selective catalytic reduction?SCR?closed loop control system is used to clear the exhaust gases,through the injection of urea in tail gas,urea thermal-decomposes to ammonia and reacts with NO_x.So high-performance ammonia sensor,with anti-interference of NO_x,is needed to monitor NH₃ concentrations downstream of the SCR catalysts and avoid the ammonia leakage due to overdosing.In all kinds of NH₃ sensors,mixed-potential NH₃sensors with its characteristics of simple structure,sensitive response,high temperature resistant,become the research hotspot.And its main influence factor is the sensitive electrode material.Ferrite AFe₂O₄ with its great chemical stability and superior catalytic properties causes much attention.So this article take CoFe₂O₄ as sensitive electrode material,by changing the calcination method of the electrode material and electrode sintering way to change the electrode morphology,which affects the number and location of the three-phase interface on the electrode.On the basis of CoFe₂O₄ materials,this study attempts to doping Mn element,and try to change the electrode performance by changing the electrode material components,to explore how the Mn content affect the electrode sensing properties.Similarly,in order to further improve the sensitivity and selectivity of the elect rodes,in this paper we doped Zn element in the same way of Mn,to study the of Zn content and electrode sensing properties.The CoFe₂O₄ powder was prepared by the sol-gel method.Co-sintering of electrode and electrolyte has been realized.The co-sintered sensor,with a porous three dimensional network structure electrode and great adhesion with electrolyte,exhibits the largest response?about 81 mV for 320 ppm NH₃?and the highest NH₃sensitivity?55 mV/decade?with the response time and recovery time?12–14 s?at450^?,it also shows satisfying NH₃ selectivity compared with NO_x?sensitivity to NO and NO₂ are 11 and 12 mV/decade respectively?,and O₂ has few influence on the sensor responses.Mn_x Co_1-xFe₂O₄ powders were made by the sol-gel method similarily.With the increase of Mn content,the sensitivity to NH₃ of Mn_x Co_1-xFe₂O₄ electrode increase first and then decrease.Among them,the response potential of electrode Mn_0.2Co_0.8Fe₂O₄ is the highest,reach to 58 mV at 500? for 320 ppm NH₃,and its sensitivity is 42.5 mV/decades.The best working temperature of electrode Mn_0.2Co_0.8Fe₂O₄ is 500?.And it has good selectivity to CO and CH₄,but its response to NO and NO₂ cannot be ignored.In the same way,along with the increase of the content of Zn,the NH₃sensitivity of Zn_xCo_1-xFe₂O₄ electrode peak at Zn_0.2Co_0.8Fe₂O₄ and then decrease,at500? for 320 ppm NH₃,its response voltage is 73 mV,and the sensitivity value is49.1 mV/decades.The best working temperature is also at 500?.The response of the electrode Zn_0.2Co_0.8Fe₂O₄ to 160 ppm NH₃,NO and NO₂,CH₄ and CO is respectively 63,14,11,6,3 mV,compared with the electrode Mn_0.2Co_0.8Fe₂O₄,its selectivity has improved significantly.