Potentiometric Response Of Mixed-Conducting Perovskite Oxide Electrodes To Typical Hazardous Gases

Flammable and explosive,toxic and harmful gases are a great threat to human survival,and the gas sensor can convert the concentration of these gases into electrical signals such as voltage and resistance,so as to achieve the purpose of leakage warning.At present,gas sensors play an extremely important role in medical diagnosis,mineral monitoring,security monitoring and other fields.In this paper,a solid electrolyte based gas sensor for detecting hydrogen(H2),hydrogen sulfide(H2S),volatile organic compounds(VOCs)and early cable pyrolysis gas was prepared by using gadolinium doped cerium oxide(GDC)as a substrate and mixed conductive perovskite oxide as a sensitive electrode,so as to achieve high performance detection of specific gases and study their action mechanism.The sensitive electrode materials studied all exhibit unconventional positive response polarity.This study verifies the reaction mechanism of this positive response from multiple perspectives,providing new insights into the mechanism of electrochemical gas sensing,and paving the way for the development of low-cost high-performance gas sensors.The main contents of this paper are as follows:(1)Using mixed conductive perovskite structure oxide(SFT)as the sensitive electrode material,a flat-plate H2 sensor(SFT/GDC/Pt)based on GDC solid electrolyte was fabricated.The gas sensitive properties of the sensor were systematically tested and compared with those of traditional perovskite electrode material(LSCF).The sensors SFT/GDC/Pt and LSCF/GDC/Pt show good response performance,selectivity and long-term stability to H2.It is worth mentioning that the response direction of the sensor SFT/GDC/Pt to H2 shows an opposite trend to the traditional perovskite material LSCF,which verifies that the LSCF/GDC/Pt conforms to the mixed potential theory,and the positive polar response of the sensor SFT/GDC/Pt may be based on a new gas-sensing mechanism.(2)The excellent sensing performance of mixed conductive perovskite oxide SFT and the unconventional gas-sensitive mechanism of positive polarity response are demonstrated,which can be used to enhance and optimize various sensor properties.The typical hybrid conductor material SFT shows excellent hydrogen sensitivity,selectivity,moisture resistance and long-term stability.In collaboration with LSCF materials,a hydrogen sensor with reverse-responsive bioxide electrodes was designed to provide 1.5～2.0 times greater response,sensitivity,and selectivity than conventional sensors,with a LOD of 16 ppb.At 500℃,the response values of SFT/GDC/LSCF sensor to 100 ppm and 1000 ppm hydrogen are 67.8 mV and 166.1 mV,respectively.Unlike conventional theory,the unconventional response direction of SFT is attributed to chemically induced surface electrostatic effects,and similar positive polarity responses have been observed in various mixed conducting perovskite oxides.(3)The gas sensitive properties of SSC/GDC/Pt flat type H2S sensor were designed and tested,and the response mechanism of SSC/GDC/PT was explained by relevant characterization methods.The sensor’s response to 5 ppm H2S at 400℃reached a value of 35.1 mV,and the detection limit of the actual test can be extended to the low concentration range below 0.5 ppm,calculating LOD as low as 8.6 ppb.At the same time,the sensor also shows good selectivity,long-term stability and repeatability.(4)A mixed-conducting perovskite oxide BSCF was synthesized and applied to the detection of dangerous gases.At the same time,the gas sensitive mechanism of the material was studied.BSCF/GDC/Pt plate type dangerous gas sensor was designed and manufactured,and its gas sensitivity to H2S,VOCs and other gases was investigated.The experimental results show that the BSCF/GDC/Pt sensor can quickly and accurately detect low concentration H2S(≤ 0.5ppm),and the DOP(95.3 ppt)response value of the bubble intake air at room temperature(25℃)at 400℃reaches 195.2 mV,and has excellent stability and repeatability.Next,the sensor is used to test the gas sensitivity performance of early cable pyrolysis gas of six brands of cables at home and abroad,and the detection effect is good,and the early detection and warning of cable fire is realized.