SnO₂/Co₃O₄ nanofibers using double jets electrospinning as low operating temperature gas sensor

SnO₂/Co₃O₄ nanofibers (NFs) are synthesized by using a homopolar electrospinning system with double jets of positive polarity electric fields. The morphology and structure of SnO₂/Co₃O₄ hetero-nanofibers are characterized by using field emission scanning electron microscope (FE-SEM), transmission electron microscope (TEM), x-ray diffraction (XRD), and x-ray photoelectron spectrometer (XPS). The analyses of SnO₂/Co₃O₄ NFs by EDS and HRTEM show that the cobalt and tin exist on one nanofiber, which is related to the homopolar electrospinning and the crystallization during sintering. As a typical n-type semiconductor, SnO₂ has the disadvantages of high optimal operating temperature and poor reproducibility. Comparing with SnO₂, the optimal operating temperature of SnO₂/Co₃O₄ NFs is reduced from 350℃ to 250℃, which may be related to the catalysis of Co₃O₄. The response of SnO₂/Co₃O₄ to 100-ppm ethanol at 250℃ is 50.9, 9 times higher than that of pure SnO₂, which may be attributed to the p-n heterojunction between the n-type SnO₂ crystalline grain and the p-type Co₃O₄ crystalline grain. The nanoscale p-n heterojunction promotes the electron migration and forms an interface barrier. The synergy effects between SnO₂ and Co₃O₄, the crystalline grain p-n heterojunction, the existence of nanofibers and the large specific surface area all jointly contribute to the improved gas sensing performance.