Preparation And Properties Of WO₃Gas Sensor

Science and technology is a double-edged sword. With the promoting of science and technology, the automobile industries develop rapidly. All kinds of cars appear in the streets in the world. The cars indeed bring great convenience to people’s life. However, environmental pollution inevitably produces, especially the atmospheric pollution. NOx gas emitted by automobile exhausts has bad effects on global environment and human beings. In order to reduce the emissions of NOx gas, a NOx gas sensor must be used to monitor the content of NOx gas, which making the car off-gas treatment system operated more effectively. Because of the harsh environment of the automobile exhausts, a mixed-potential NOx sensor based on YSZ has become a competitive candidate of detecting automobile exhaust. The mixed potential sensor has many advantages such as simple construction, fast response and strong sensitivity. Most importantly, the sensor is likely to replace the amperometric NOx sensor which has been put into use in cars for detecting the exhausts. Therefore, researchers spent much time and energy to research, develop and design the mixed potential NOx sensor. The author discussed the relationship between the morphologies of sensing electrode materials, explained the process of electrode reaction from the microscopic view. So this essay mainly consists of three parts:(1) Planar NOx sensor based on YSZ has been fabricated. Sensing electrode was commercial WO3, ball-milling WO3, WO3nanoplates and WO3nanoparticles, respectively. Reference electrode was Pt and PtY, respectively. The potential difference of sensors with different morphologies WO3sensing electrode was measured at different concentrations of NO gas, different temperatures. The results show that sensors with nano-WO3sensing electrode possess good sensing performance, especially the sensor with WO3nanoplates sensing electrode. And sensing performance of sensor with PtY reference electrode was better than sensor with Pt reference electrode. Moreover, the best operating temperature of sensor was500℃and550℃. In addition, the stability testing and the testing of interference from CO2, H2O were also performed. The results show that, compared with sensor with ball-milling WO3sensing electrode, sensor with WO3nanoplates sensing electrode possessed large sensitivity (500℃, sensitivity was52.2mv/decade), the stability of sensor and the ability of anti-interference gas were also superior to sensor with ball-milling WO3sensing electrode.(2) For sensor with ball-milling WO3sensing electrode and sensor with WO3nanoplates sensing electrode, the electrochemical impedance spectroscope measurements was performed at different concentrations of NO gas and different temperatures. The electrochemical impedance spectroscope shows that electrode reaction occurred at the TPB of YSZ-sensing electrode-gas was gradually enhance with increasing concentration of NO gas. The catalytic activity of the anodic reaction (reaction between NO and O2-) increased with increasing concentration of NO gas. Moreover, the catalytic activity of the anodic reaction for sensor with WO3nanoplates sensing electrode was higher than sensor with ball-milling WO3sensing electrode. In other words, the process of electrode reaction of sensor with WO3nanoplates sensing electrode was stronger than sensor with ball-milling WO3sensing electrode, which indicated that why the sensing performance of sensor with WO3nanoplates sensing electrode was better than sensor with ball-milling WO3sensing electrode.(3) The relationship between sensing electrode thickness and sensing properties was discussed. The results show that the thiner the sensing electrode, the larger the sensitivity.