Influence of sintering temperature on the physical, electrochemical and sensing properties of α-Fe2O3-SnO2 nanocomposite sensing electrode for a mixed-potential type NOx sensor

The Influence of sintering temperature on the physical, electrochemical and sensing properties of alpha-Fe2O3-SnO2 nanocomposite sensing electrode for a mixed-potential type NOx sensor is investigated. The alpha-Fe2O3-SnO2 nanocomposite was synthesized by a solution combustion route and sintered at temperatures 900, 1000, 1100 and 1200 degrees C to form the sensing electrodes of a stabilized-zirconia based mixed-potential type NOx sensor. The influence of sintering temperatures on the physical properties was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and N-2 adsorption-desorption isotherm measurements. The gas sensing measurements were conducted at an operating temperature of 650 degrees C. A systematic increase in the response/recovery times was observed with an increase in the sintering temperature from 900 to 1200 degrees C. An optimum microstructure with a low surface area and large pore size leading to high electrochemical reactions at the interface and low heterogenous gas-phase decomposition of NO2 resulted in the maximum response magnitude (Delta V) and sensitivity for the electrode sintered at 1000 degrees C. Furthermore, the effect of sintering temperature on the electrochemical activity of the sensing electrode and its co-relation with the sensing properties was studied by dc polarization curve measurement. Moreover, the microstructure, sensing response, sensitivity, dynamics and O-2 conc. dependence of the presented mixed-potential type NOx sensor is critically dependent upon the sintering temperature of the sensing electrodes.