Effects of sintering temperature on sensing properties of WO₃ and Ag-WO₃ electrode for NO₂ sensor

Pure WO₃ and Ag-WO₃ (mixed solid solutions Ag with WO₃) have been successfully synthesized by sol-gel method and the influences of calcination temperature on the particle size, morphology of the WO₃ and Ag-WO₃ nanoparticles were investigated. Powder X-ray diffraction results show that the hexagonal to monoclinic phase transition occurs at calcination temperature varying from 300°C to 500°C. SEM images show that calcination temperature plays an important role in controlling the particle size and morphology of the as-prepared WO₃ and Ag-WO₃ nanoparticles. The NO₂ gas sensing properties of the sensors based on WO₃ and Ag-WO₃ nanoparticles calcined at different temperatures were investigated and the experimental results exhibit that the gas sensing properties of the Ag-WO₃ sensors were superior to those of the pure WO₃. Especially, the sensor based on Ag-WO₃ calcined at 500°C possessed larger response, better selectivity, faster response/recovery and better longer-term stability to NO₂ than the others at relatively low operating temperature (150°C).