NiO-based Heterojunction Gas Sensor Array For SF₆ Decomposed Components Detection And Its Characteristics

Improving the insulation level of the rural low-voltage distribution network is an important measure to further promote the construction of"first-class distribution network",narrow the gap between urban and rural areas and ensure the safe and reliable operation of the rural power system.Sulfur hexafluoride（SF₆）decomposition component detection is an effective method to determine the early latent fault type and severity of SF₆ gas insulated equipment.Gas sensor detection technology is the research core of SF₆decomposition component detection,and gas sensor array technology is the direction of multi-component gases detection.Typical characteristic gases such as H₂S,SO₂ and SOF₂will inevitably exist in SF₆ gas insulated equipment under the action of different degrees of discharge fault and trace moisture and oxygen.The on-line evaluation of equipment insulation performance and operation status can be realized by detecting the type and concentration of characteristic gases.Nickel oxide（Ni O）has been widely used in experimental research and commercial application due to its own catalytic properties and multi-dimensional hierarchical structure.However,Ni O-based gas sensors still have some disadvantages,such as low responses and serious cross-sensitivity.In order to promote the basic research and application of Ni O-based gas sensor,it is imperative to realize the performance control of the sensor through morphology and structure modification.At the same time,the research of cross sensitivity suppression and multi-component gas quantitative detection through the construction of sensor array also needs to be explored.This paper relies on the project of the National Natural Science Foundation of China.In this paper,WO₃-Ni O and SnO₂-Ni O heterojunction gas sensing materials with multi-dimensional hierarchical structures were prepared to detect characteristic gases H₂S,SO₂and SOF_2.The morphology and structure of the synthesized sensing materials were characterized,and the potential gas sensing performance optimization mechanism of WO₃-Ni O and SnO₂-Ni O composite sensing materials was discussed from the perspective of microscopic characterization.The response characteristics of the gas sensors to SF₆decomposition components H₂S,SO₂ and SOF₂,were tested on the platform.Based on the beneficial morphology of hierarchical structure and the electron depletion layer theory of heterojunction,the gas sensing response mechanism and the modified sensitization mechanism of WO₃-Ni O and SnO₂-Ni O gas sensors were explained.Finally,based on the established generalized regression neural network model,the concentration prediction of multi-component gas H₂S,SO₂ and SOF₂ are realized.The main research work and conclusions are as follows:（1）The flower-like nanostructures of pure NiO and WO₃-Ni O composite were prepared by hydrothermal method.The successful introduction of WO₃ and its beneficial effects on flower-like structure were verified by XRD,EDS,SEM,TEM,XPS and BET analysis.Based on the gas sensing test platform,the gas sensing characteristics of SF₆decomposition components H₂S,SO₂ and SOF₂ were tested.The test results showed that the responses of WO₃-Ni O based gas sensor were 33.34,15.37 and 8.73,respectively,4.4,3.7 and 4.0 times of pure Ni O-based sensor.The study of sensitization mechanism shows that the more excellent gas sensing performance of WO₃ Ni O based gas sensor is due to its dense flower-like structure,which provides a large specific surface for gas molecular adsorption,and the efficient regulation of carrier concentration by heterojunction in the complex.（2）The smooth sphere of pure Ni O and needle-anchored sphere of SnO₂-Ni O composite were prepared by hydrothermal method.The successful introduction,uniform dispersion and close contact of needle-like SnO₂ with Ni O were proved by various morphologies and structural characterization methods.The results show that the responses of SnO₂-Ni O based gas sensor for detecting H₂S,SO₂ and SOF₂ is 4.31,9.42and 2.98 respectively,while the sensitivity of pure Ni O based gas sensor is only 2.29,3.17 and 1.16.At the same time,SnO₂-Ni O based gas sensor has a lower working temperature（230℃）,prominent linearity,excellent repeatability and stability.Further mechanism studies show that compared with pure Ni O-based gas sensors,the loose and rough surface morphology of needle-anchored SnO₂-Ni O sphere provides more active sites and residence time for the adsorption and diffusion of gas molecules.The regulation of heterojunction on the width of conductive channel and depletion layer are both the main reasons for the enhanced performance of the sensor.（3）Aiming at the cross-sensitivity of the sensor to three SF₆ decomposition components H₂S,SO₂ and SOF₂,a four-unit gas sensor array was designed using WO₃-Ni O,SnO₂-Ni O and two corresponding pure Ni O-based sensors.The responses sample database was established based on the gas sensing response results of the array to three characteristic gases,and the generalized regression model was established under the optimal smoothing factor of 0.1.At the same time,the prediction performance of the model is verified by testing samples.The results show that the average relative errors of H₂S,SO₂ and SOF₂ predicted by the model are 8.15%,8.90%and 8.32%,respectively.Compared with BP neural network,the model has higher prediction accuracy and realizes the suppression of cross-sensitivity phenomenon and effective prediction of SF₆decomposition gas concentration.