Fundamental Research On Sensitivity And Selectivity Of SnO₂-based CO Sensor

The present aimed to increase the sensitivity and selectivity of SnO2. SnO2-based materials were prepared by sol-gel method. The thick films of SnO2-based materials were prepared by screen printing method. The composition, morphology and electrochemical property of the material were characterized by XRD, SEM and electrochemical workstation respectively. After all these, CO sensors were prepared. The main results and innovations were summarized as follows.Pd-loaded and Fe-doped SnO2was prepared by sol-gel method. The results showed that Pd-loaded and Fe-doped SnO2had the same crystal structure as pure SnO2, the crystalline degree was reduced with the increasing of doping amounts of Fe. In addition, when adding amounts were0.2mol%Pd and10mol%Fe, the composite had the highest sensitivity and selectivity to CO in range of200-3000ppm at350℃. At the same time, it was found that Fe doping contributed mainly to the improvement of the selectivity of CO against H2, and the further Pd loading enhanced the selectivity function of Fe. With further study on the Au loading, Pt loading and In doping, it was showed that both Au loading and In doping were helpful to improve the selectivity to CO while Pt loading was helpful to improve the selectivity to H2.Through the investigation of the response value of the SnO2sensor in N2, N2+O2and N2+O2+H2co-existed gas atmosphere, the effects of hydrogen and oxygen on the resistance value were investigated, and it was concluded that adsorbed oxygen mainly controlled the conduction of SnO2through forming a grain boundary barrier but not surface chemical reaction. With further research on the response value of SnO2to H2and CO under the background gas of N2in different temperatures, it turned out that the product of surface chemical reaction was OH" or CO32-but not H2O or CO2which can be obtained in air.In order to realize the precise quantification of gas concentration, the relationship between the gas concentration and the response value (R=1+kCn) was investigated. It turned out the n value is independent of the change of sintering temperature between600-800℃, the modification way (Pd-loading and Fe-doping) and the kinds of the target gas. However, the n value was mainly affected by the fabrication type and working temperature.In the end, base on the properties of Pd, Fe and Pt-modified SnO2, the selectivity to CO or H2and the detection of the mixed gas of CO and H2, the "Equation Set" was set up according to the response curve of the two sensors to the mixed gas, thus, we calculated the concentration of CO and H2by solving the "Equation Set". Contrast real values with calculated values of CO and H2concentration, the error margins were all less than5%, which indicates that this method is a promising candidate for enhancing the selectivity in two or more kinds of gases.