Microstructure evolution and gas sensitivities of Pd-doped SnO2-based sensor prepared by three different catalyst-addition processes

We have investigated three ways of impregnating PdO on an SnO2 gas sensor to achieve a simple and reliable sensor-fabrication process. These impregnating processes are: (1) coprecipitation of SnO2 and Pd compounds in the solution; (2) addition of PdCl2 to SnO2 gel, followed by precipitation; and (3) infiltration of PdCl2 into calcined SnO2 powder. Processes (1) and (2) introduce Pd into SnO2 particles before particle growth is completed. The phase and microstructures of particles have been analysed by X-ray diffraction, scanning and transmission electron microscopes, and an energy-dispersing X-ray spectroscope. The presence of Pd in the process of SnO2 precipitation restrains the growth of SnO2 particles and enhances a uniform distribution of fine PdO powder on the SnO, grains. SnO2 gas sensors have been fabricated and tested for response to CH4, C2H6 and CO. Processes (1) and (2) show many possibilities of improving SnO2 gas-sensor sensitivity with a simplified fabrication process.