A novel nanostructured material composed of WS2/WO2.9/C membranes with free-standing and flexible feature, which were synthesized via a two-step heat treatment of ammonium tetrathiotungstate ((NH4)2WS4) and polyacrylonitrile (PAN) spin-coated onto graphite foils. These two precursors decompose at high temperature (850°C) forming WS2 and C species, while the introduction of trace amount of oxygen leads to the formation of WO2.9 nanowires. First, (NH4) 2WS4 and PAN were dissolved in N,N-dimethylformamide (DMF). The mixture was stirred until a homogeneous solution was formed. The precursor solution was then spin-coated onto a substrate. After drying under ambient conditions, the coated substrate was loaded into a chemical vapor deposition (CVD) system for thermal treatment in the presence of sulfur. The precursor on the substrate was first annealed at 500°C in Ar/H2 flow to decompose (NH4) 2WS4, and then heated up to 850°C and annealed under an Ar flow and vaporized sulfur, finally the system was allowed to cool down to room temperature. Trace amounts of oxygen were induced into the CVD system during the cooling process, thus leading to the formation of tungsten oxide at 700°C. As-synthesized WS2/WO2.9/C samples on graphite foils exhibit excellent mechanical flexibility. Scanning transmission electron microscopy (STEM) coupled with high-angle annular dark-field (HAADF) imaging, reveals the fine structure of the WS2/WO2.9/C sample. STEM-EDS mappings indicate that the distributions of S and O are correlated with W, while the density of C is rather low in W-rich regions, thus implying that tungsten sulfide and oxide are the main phases. In addition to elemental distribution, electron microscopy also reveals the crystalline structure of the WS2/WO2.9/C hybrid. High-resolution TEM (HRTEM) image demonstrates widely separated fringes with the closest spacing of 0.62 nm, which is in agreement with the d-spacing of of 2H-WS2.
All Science Journal Classification (ASJC) codes
- Materials Science(all)
- Mechanics of Materials
- Mechanical Engineering