While numerous types of gas sensors have been developed for various industries and applications such as automotive industry, environmental monitoring, and personal safety, nanoscale chemiresistive gas sensors have gained significant research interest due to several advantages such as high sensitivity, low power consumption, and portability. An essential component of these gas sensors is the sensing material where metal oxide semiconductor (MOS) materials are the most prevalent sensing material. Different nanostructures and types of MOS have been reported where 1-D nanostructured sensing materials (e.g., nanofibers, nanowires, nanorods, etc.) been the preferred materials type for gas sensor development due to the inherent geometrically higher surface-area-to-volume ratio. This contributes to increased ability adsorbing gas analytes and more significant modulation of electrical properties upon exposure to analytes due to the broader interaction zone over cross-section area. Among the MOS, tungsten trioxide is well known for the application in photocatalyst, photochromic, photoelectrodes, hydrogen production and most importantly gas sensors. WO3 has attracted much attention in gas sensing due to its high sensitivity toward various analytes, chemically and thermally stable at room temperature and controllable synthesis, which enabled WO3 being one of the most promising sensing materials in gas sensor. Therefore, electrospinning is the most suitable technique to synthesize 1-D structured WO3 because of the simple process, ease of controlling composition and morphology and high yield. As one of the top choices for sensing material, however, gas sensing performance (i.e., sensitivity and selectivity, etc.) of WO3 based gas sensor still required improvement. Hence, several strategies including diameter minimization, grain size and crystallinity control and noble metal doping/decoration have been employed in this work for the purpose of enhancing gas sensing performance.Based on a 2-factor design of experiments (DOE), diameters of synthesized WO3 nanofiber ranged from 23 to 209 nm. No remarkable enhancement of gas sensitivity observed from smaller diameter WO3 nanofibers, which could be ascribed to the dominating of grain size effect on gas sensing in polycrystal WO3 nanofibers. Pd and Au doped 50 nm WO3 nanofibers were synthesized as well of which morphology, composition and crystalline were confirmed via SEM, TEM and XRD analysis. As a result, 2-Au-WO3, 5-Au-WO3 and 1-Pd-WO3 exhibited significant sensing improvement toward ethanol and methane, acetone and toluene, respectively.
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