Hole-supply-rate-controlled methanol-gas-sensing reaction over p-type Co3O4/single-walled carbon nanotube hybrid structures

Co3O4/single-walled carbon nanotube (Co3O4/SWCNT) hybrid structures are fabricated, and their methanol sensing properties and related sensing principles are systematically investigated. A series of Co/SWCNT nanohybrid structures are deposited on silicon dioxide substrates by a co-arc discharge process and converted to Co3O4/SWCNT nanohybrid structures by subsequent methanol treatment and oxidation processes. The morphologies and structures of the nanohybrid composites are investigated by scanning electron microscopy, transmittance electron microscopy, X-ray diffraction, and Raman spectroscopy. The effect of the nanohybrid film thickness and the Co3O4: SWCNT ratio in the films on their physical and gas sensing properties are systematically examined. The best methanol-sensing performance is observed upon measurement at 300 °C for the material fabricated by deposition for 15 min and oxidized at 500 °C. The enhanced gas-sensing performance of the hybrid nanostructures is analyzed to prove that the high carrier supply rate from the transducer determines the reaction rate on the receptor surface (providing the receptor can accommodate the oxygen ionosorption). The hybrid sensor structures also exhibit low detection limit of 50 ppb, good selectivity, repeatability, and long-term stability, demonstrating their potential for practical application to methanol sensing. © 2020 Elsevier B.V.