Impedancemetric-type NO2 sensor based on non-stoichiometric perovskite type sensing electrode using multiple response signals

Abstract

Perovskite-type oxides have received considerable attention as sensing electrode (SE) for solid electrolyte type sensors because of their exceptional sensing performance and compositional flexibility. Herein, non-stoichiometric perovskite oxides (La0.75Sr0.25)xCrO3-δ (x = 0.95, 1.0, 1.05) with nano-structure were prepared in porous YSZ backbone by impregnation method as SE for impedancemetric-type NO2 sensor. Because of the non-stoichiometry of SE, the NO2 adsorption capacity and electrochemical activity of SE are effectively enhanced. Consequently, the sensors based on non-stoichiometric SEs exhibit noticeably improved sensitivity to NO2. Meanwhile, instead of module value (|Z|) as response signal in traditional impedancemetric-type NO2 sensor, various parameters including resistive component (Z′), capacitive reactance (Z″), |Z| and phase angle (Θ) extracted from impedance spectra were explored as the response signals for the present sensor. The sensors using all the extracted signals show excellent sensing performances in NO2 concentration range of 100−700 ppm. Compared with sensor using Z′ or |Z| response, the sensor using Z″ and Θ response can operate at higher frequencies and shows much better selectivity against CH4, CO2 and H2. Using Z″ as the response signal, the sensor exhibits a higher sensitivity to NO2 than that with other parameter as signal, because the response ΔZ′′ values vary linearly with respect to NO2 concentrations instead of logarithmic relation.