Fabrication of tungsten oxide nanofibers via electrospinning for gasochromic hydrogen detection

The application of tungsten oxide nanofibers for gasochromic hydrogen sensing is reported. Three tungsten oxide nanofibrous webs were fabricated by electrospinning proxopolyltungestic acid incorporated in polyvinylpyrrolidone. The samples were then calcinated to remove Polyvinylpyrrolidone to obtain tungsten oxide nanofibers. The tungsten oxide nanofiber samples had a grain form with an average fiber diameter of 103 nm, 181 nm and 293 nm. The tungsten oxide nanofibrous webs showed a very good sensitivity to concentartions of hydrogen (in argon) as low as 2% at room temperature. This is very important as the electrical hydrogen gas sensors need high temperatures to sense hydrogen. Upon contacting hydrogen, the almost colorless nanofibers turn into blue in less than 2 min. Cyclic hydrogen – oxygen exposure showed that the samples could be reused after two cycles. XRD, Raman and FTIR analysis showed a monoclinic crystalline structure for tungsten oxide (WO3). After exposure to hydrogen which resulted in the formation of tungsten oxide bronze (H0.23WO3), the original monoclinic structure changed to tetragonal. After the removal of hydrogen and exposure to air, the samples gain back the monoclinic structure. XPS analysis revealed that the presence of a low amount of palladium chemical phase is sufficient for active sites of WO3 to continue sensing hydrogen gas.