Preparation Of CeO₂-based Nanomaterials And Their Hydrogen Sensing Properties

H₂ has great application value as a high-efficiency clean energy.However,due to its flammable and explosive characteristics,there are risks in the process of production,storage,transportation,and use.In order to detect the leakage of H₂timely and effectively,the development of hydrogen sensor with highly sensitive,good selectivity and stability is imminent.Although CeO₂has problems such as low response to H2 and poor selectivity,this paper modified CeO₂by controlling the morphology and forming a heterojunction by compounding the second phase,and obtained CeO₂ nanomaterials with good response to H₂.At the same time,it also has a low optimal temperature,good selectivity and stability.And the study found that the abundant oxygen vacancies in CeO₂have a unique response mechanism to H₂in different detection atmospheres.This study is of great significance for the hydrogen sensing performance research of CeO₂-based materials.The main research contents are as follows:1.CeO₂ nanorods with a diameter of about 10 nm and CeO₂nanospheres with a diameter of less than 100 nm were synthesized,all of which have high purity and crystallinity.The gas sensing results show that CeO₂nanorods have lower optimal response temperature(100°C)and higher response,and the response value changes linearly with the concentration.The response values??for 1000 ppm and 4000 ppm H₂are 1.61 times and 1.72 times higher than CeO₂nanospheres,respectively.At the same time,CeO₂nanorods also have relatively short response/recovery time,good cyclability,excellent selectivity and long-term stability.The studies believe that CeO₂nanorods have the best hydrogen sensing performance not only because they have a larger specific surface area that can absorb more gas,but also because the small size effect of one-dimensional materials changes the way the material's carriers are transported.It not only makes the CeO₂nanorods covered by the depletion layer,which brings about a huge change in the resistance value,but also weakens the influence of the barrier at the grain boundary,directly affects the carrier transmission mode,and greatly improves the response value.2.In₂O₃ nanoparticles were loaded on CeO₂ nanorods by precipitation method to obtain the CeO₂@In₂O₃nanocomposites.In₂O₃was mainly uniformly supported on CeO₂nanorods in clusters.The composite In₂O₃adjusts the band gap of the material.The hydrogen sensing performance test shows that the optimal temperature of the composite material is unchanged.Among them,the 10 wt%CeO₂@In₂O₃sample has the highest response value,and the response values??to 1000 and 4000 ppm H₂are2.79 times and 2.43 times higher than the uncombined CeO₂,respectively.The response value changes linearly with the detection concentration.It also has enhanced H₂selectivity,good recyclability and long-term stability.On the one hand,it is due to the synergy between the metal oxides that make up the composite material.On the other hand,the n-n heterojunction adjusts the band gap,which not only adjusts the band gap,but also forms a depletion layer and an additional electron accumulation layer,resulting in moreO₂molecular adsorption,it also forms a"built-in electric field"to separate the charge carriers.The role of current carriers increases the density of charge carriers and improves the performance of the hydrogen sensor.3.We explored the hydrogen sensing properties of CeO₂in different atmospheres by taking CeO₂nanorods as the main research object.The XPS test results show that there are a lot of Ce in the+3 and+4 valence states on the surface of CeO₂,shows that there are a lot of oxygen vacancies on the surface of CeO₂.The analysis shows that CeO₂has a unique response mechanism to H₂;N₂has small effect on the resistance of CeO₂at low temperatures;the occurrence of atmosphere conversion(aerobic?anaerobic)has a huge impact on this unique response mechanism.At the same time,it is verified that CeO₂has a good response and excellent selectivity to H₂under anaerobic conditions.The analysis believes that oxygen vacancies play a key role in the unique response mechanism:VO¨and Ce Ce'will form(V_O¨Ce _Ce')^·.The paired clusters act as the“traps”of electrons,restricting the free transmission of electrons,causing the resistance to increase abnormally;when the test environment regainsO₂,O₂molecules quickly dissolve in the lattice of CeO₂,then the(V_O¨Ce _Ce')^·is separated,and electrons are released,which causes the resistance to drop to the lowest instantaneously.After that,O₂adsorbs on the CeO₂surface to form oxygen species,and the resistance resumes a steady upward trend.This basic research has important and pioneering significance for the follow-up in-depth exploration of CeO₂ hydrogen sensors.