Enhanced sensing performance of the amperometric NO2 sensor by use of a mixed conductive porous layer

Abstract

A novel amperometric NO2 sensor was fabricated using a nanostructured La0.8Sr0.2MnO3-δ (nano-LSM) sensing electrode (SE) and a Ce0.8Gd0.2O1.9 (CGO) electrolyte. The focus of this study was to extend the electrochemical active site at the three-phase boundary (TPB) and reduce the interfacial resistance by introducing a hybrid ion/electron conducting porous layer (CGO +LSM) between the SE and the electrolyte. By adjusting the amount of LSM, the effects of the LSM/CGO ratio on the microstructure and sensitivity of the sensor were investigated. The results showed that the addition of LSM did not change the porous structure of the CGO porous skeleton, but the number of pores decreased with the increase of LSM addition, while the size of pores increased with increasing the amount of LSM added. The nano-LSM was prepared in-situ into the porous skeleton by the impregnation technology, which was highly dispersed in the porous skeleton, having reached the bottom of the porous layer with a particle size of less than 100 nm. The sensor with a mixed conductor as the porous layer effectively improved the sensitivity of the sensor. Analysis by electrochemical impedance spectroscopy (EIS) and the distribution of relaxation techniques (DRT) demonstrated that the addition of the electronic conductor LSM into the CGO porous layer significantly reduced the diffusion resistance of the sensor and enhanced the oxygen exchange performance, thus improving the response performance of the sensor. The sensor with 30wt% LSM/CGO porous layer had good reproducibility and excellent stability. The sensor had good anti-interference performance against co-existing CH4, CO2, H2, NO, and NH3, with good linearity between sensor response values and NO2 concentrations over different O2 concentrations and relative humidity (RH).