NO₂ Gas Mixed-potential Sensor Based On Different Solid Electrolyte Materials

Due to the degradation in environment worldwidely,especially the harms resulting from air pollution,people pay much more attention to environmental issues than ever before in the history.Among the major polluting gases such as vehicle exhaust and industrial exhaust gases,NO_x accounts for a large proportion,having given rise to various disasters such as acid rain and photochemical smog.The current quantitative analysis of NO_x gas,including chemiluminescence method,spectrophotometry method and Saltzman method,etc.,is by means of collecting sample gas and bringing back to laboratory for instrumentally detecting.Since the composition in target gas changes dynamically,such lab-based analyzing results are actually time-delayed.Meanwhile,they have other disadvantages of low efficiency and high cost,although they may provide accurate quantitative volume.The solid electrolyte gas sensor has been recognized one of the best way to detect low concentration NO_x gas real-time,for its excellent gas sensing performance and economic benefits.In this paper,three different solid electrolyte material substrates,GDC,YSZ and NASICON,were prepared by casting and die pressing.With combination of sensitive electrode materials such as P25 and WO3,three electromotive force type NO₂ gas sensors were developed.A series of tests were carried out on the performance of the sensor,such as response sensitivity,response time,stability,repeatability,and selectivity.The results show that the response values ?V of three sensors having linear relationships with the logarithm of the NO₂ gas concentration,which is well consistent with the working mechanism of hybrid electromotive force unit.The influence of the operating temperature is analyzed for the YSZ solid electrolyte-based sensor,revealing that the operating temperature has a greater influence on the response value and response time.In particular,the NASICON electrolyte mixed potential NO₂ gas sensor,which was firstly developed by using a positive temperature coefficient ceramic material?PTC?as the heating source to attain self-constant temperature for sensor working,achieved good response of 84.60 m V/decade against the NO₂ gas concentration ranging from as low as 5ppm to 150 ppm at the highest,in addition to other advantages in feasibility and stability as well,which are considered necessary performances for a high grade gas sensor.Such a simple heating mechanism will definitely provide a new solution for portable and low cost sensors for various gases detections.