Synthesis of V2O5-Co3O4 Nanoassemblied Spheres for Gas Sensing Applications

Under the development of high industrialization, the excess of greenhouse gases has caused a global climate crisis, and thermal power generation is one of the primary sources of greenhouse gas emissions. With the rising awareness of energy conservation and carbon reduction in major industrial countries in recent years, the energy transition has become an important issue. At present, hydrogen energy is a potential sustainable energy source. The most significant advantage of using hydrogen (H₂) fuel to generate electricity is that it significantly reduces carbon dioxide emissions. However, the combustion of H₂ will still form nitrogen dioxide (NO₂), and exposure to NO₂ will cause damage to the human respiratory tract, lungs, and kidney functions. To reduce the risk of hydrogen leakage, explosion, and nitrogen dioxide harm to the human body, developing highly-sensitive gas sensing materials for detecting hydrogen and nitrogen dioxide has become an essential goal with great forward-looking and industrial application potential.
In this study, vanadium pentoxide (V₂O₅) and cobalt tetroxide (Co₃O₄) nanoassemblies with different morphologies were respectively successfully synthesized by the polyol method at different reaction temperatures. The synthesized V₂O₅ nanoassemblies can exhibit high-performance H₂ sensing properties at room temperature without catalyst modification. The Co₃O₄ nanoassemblies showed the highest response to NO₂ at an operating temperature of 130 ^oC. In addition, in the later stage of Co₃O₄ synthesis, vanadium acetylacetonate V(acac)₃ was introduced to form Co₃O₄-V₂O₅ nano-mixed particles. Finally, a novel heterogeneous core-shell nanoassembly structure comprised a Co₃O₄ core and Co₃O₄- V₂O₅ mixed nanoparticle shell. When V₂O₅, an n-type oxide, is assembled with Co₃O₄, a p-type oxide, the formed p-n junction will result in a depletion region. The electrical charge increases when the target gases are adsorbed and desorbed, improving the sensing sensitivity. The specific surface area of the V₂O₅-modified Co₃O₄ nano-assembled spheres is 3.2 times that of the Co₃O₄ nano-assembled spheres. At 130 ^oC, the sensitivity to 400 ppm NO₂ increased from 247 % to 421 %. The gas-sensing responses of the synthesized nano-assemblies are all reproducible through cyclic measurements. Compared with CH₄, C₂H₆, C₃H₈, CO, NO gases, V₂O₅ and V₂O₅ modified Co₃O₄ nanoassembles showed excellent selectivity for H₂ and NO₂, respectively.