A novel impedancemetric NO2 sensor based on nano-structured La0.75Sr0.25Cr0.5Mn0.5O3−δ prepared by impregnating method

An impedancemetric NO2 sensor was fabricated using nano-structured La0.75Sr0.25Cr0.5Mn0.5O3−δ (LSCM) as sensing electrode and Ce0.9Gd0.1O1.95 (CGO) as electrolyte with bilayer structure including both a dense layer and a porous layer. The LSCM particles were prepared in the porous CGO layer by impregnating method. The composition and microstructure of materials were characterized by XRD and SEM, respectively. The properties of the sensor were studied using electrochemical impedance spectroscopy in the temperature range of 400–600 °C. An equivalent-circuit model was used to extract fitting parameters from the impedance spectra for a preliminary analysis of NO2 sensing mechanism. The results showed that the LSCM particles with 100–200 nm in diameter were dispersed throughout the porous CGO layer. The decrease of impedance semicircle in low frequency with increase of NO2 concentration was associated with the changes of low-frequency resistive component. The response signals ((|Z|base − |Z|sample)/|Z|base) of the sensor at 0.1 Hz were found to vary almost linearly with the NO2 concentrations from 0 to 400 ppm. The sensor showed good response–recovery characteristics and reproducibility. The response signals of the sensor were slightly affected by coexistent O2 varying from 0 to 10 vol%.