Study On CH₄ Detection Characteristics Of Pd²⁺ Doping SnO₂ Nanoparticle Gas Sensor

As the core equipment in the electrical power system, the power transformer can interrupt the power supply and causing huge economic losses. Nowadays, dissolved gas analysis becomes one of the most effective methods for detecting faults in oil-immersed power transformers. Methane gas(CH4) is one of the most important arc discharge characteristic gases dissolved in power transformer. The gas sensor technology is the key of online monitoring and analyzing gases dissolved in transformer oil. As the commonly used semiconductor gas sensor, Stannic oxide(SnO2) is early developed, the most widely used and sensitive to all types of fault characteristic gases; but also has the problems of high operating temperature, low sensitivity and cross sensitivity. When used for CH4 detection,we are funded by the National Natural Science Foundation of China(No. 51277185) and research for detection characteristics of two ways to(surface deposition doping & atomic substitution doping) carried out Pd2+-doped SnO2 nanomaterials gas sensor to the CH4 gas dissolved. We have build SnO2 gas sensors with two different types of nanostructures, and the measurements include analysis of the temperature and density characteristics, the minimum detectable concentration, response recovery characteristics, stability and selectivity of the sensors. Based on first principles density functional theory, using the generalized density approximation method, and calculated the adsorption energy of CH4 absorbed on two ways to doping Pd2+ in SnO2, the results prove that after doping Pd2+ in SnO2, the reveals higher sensitivity to CH4. The macroscopic and microscopic simulation analysis produced the following results:We researched the gas sensing performances of surface deposition doping Pd2+ in SnO2 nanomaterials to CH4 isstudied. The samples of pure SnO2 and SnO2 doping Pd2+ with value of 1.0 wt%~3.0 wt% are composed of nanopowders and their structure is rutile type. After Pd2+ doping SnO2, the aspect ratio of nanopowders increases while powder dispersion becomes weak. Thesensing behaviors of all the samples to CH4 were systematically investigated based onthe trace gas sensing test system.The test result shows that the Pd2+ doped SnO2 gassensors have more excellent sensing performances to CH4 compared to the pure SnO2 gas sensor, and 1.5 wt% is the optimum doping content. For the detection of CH4, thesensor based on 1.5 wt% Pd2+-doped SnO2 nanopowders shows lower optimum workingtemperature, higher response, better linearity, the lower detection limit and shorterresponse-recovery time. At the same time, the component has good selectivity to CH4, and can effectively distinguish between CH4 and C2H2, CO, H2.We researched the gas sensing performances of atomic substitution doping Pd2+ in SnO2 nanomaterials to CH4 is studied. The pure SnO2 and Pd2+-doped SnO2 with doping content of 1.0 at%~5.0 at% have the similar morphology of nanoparticles and keep the same rutile structure. As the doping content of Pd2+ increases, the average particle diameter of nanospheres gradually decreases while powder dispersion becomes weak. The sensing behaviors of all the samples to CH4 were systematically investigated based on the trace gas sensing test system. According to the experimental result, we can clearly know that the Pd2+-doped SnO2 gas sensors exhibit better sensing properties to CH4 than the undoped SnO2 gas sensor, and 3.0 at% is the best doping ratio. For the detection of CH4, the sensor based on 3.0 at% Pd2+-doped SnO2 nanoparticles has lower optimum working temperature, higher sensitivity, better linear response and lower detection limit. In addition, the component shows certain selectivity to CH4.We researched the gas sensing mechanism of two ways to doping Pd2+ in SnO2 sensor. Based on first principles theory, the models of SnO2(110) face with different material and CH4 adsorption were built. This result theoretically explained that after surface deposition doping Pd2+ in SnO2 Consequently, the band gap became even narrower than the Pd2+ atomic substitution doped ones. The interaction between SnO2 surface and adsorbed gas is more frequent after gas is adsorbed at Pd2+ site.After atomic substitution doping Pd2+ in SnO2 can impurities level near the top of valence band, and the conduction band of SnO2 moved towards the low energy end.The results offer a new idea for the study of applying composite SnO2-based gas sensor to on line detect the gases dissolved in transformer oil.