Effects of WO 3 electrode microstructure on NO 2 -sensing properties for a potentiometric sensor

Planar potentiometric NO 2 sensors based on 8YSZ (8 mol% Y 2 O 3 -doped ZrO 2 ) were prepared with WO 3 sensing electrode material. The various electrode microstructures prepared by different sintering temperatures were characterized by field emission scanning electron microscopy (SEM), and the microstructure influences on the sensors' performances were investigated. The sensor sintered at 800°C, with the most reaction sites, moderate adsorption sites and appropriate electrode thickness, exhibits the highest NO 2 voltage response. While the sensor sintered at 750°C exhibits the lowest NO 2 sensitivity because of the strongest gas-phase catalytic consumption in the WO 3 sensing electrode. Based on the results of SEM characterization and electrochemical impedance spectroscopy tests, the difference in NO 2 -sensing performance was attributed to different amounts of electrochemical reaction sites at three-phase boundary, adsorption sites and different degrees of gas-phase catalysis.