Porosity and oxygen vacancy engineering of mesoporous WO₃ nanofibers for fast and sensitive low-temperature NO₂ sensing

A facile electrospinning technique combined with varied heating rates was developed to tune the porosity and oxygen vacancy of mesoporous WO₃ nanofibers. The porosity of WO₃ increased as the heating rate increased gradually up to 10 °C/min, but decreased after that value because of the destruction of WO₃ fiber-like structure. WO₃ nanofibers with a heating rate of 10 °C/min (WO₃-10) thus exhibited the largest pore size and the highest surface area. Simultaneously, as the heating rate increased, the oxygen vacancy concentration increased visibly because of locally lower oxygen partial pressure during the rapider decomposition of organic polymer at higher heating rate. Consequently, the low-temperature NO₂ sensing performances of WO₃ were modulated by the heating rate. The best sensing performances were found for the WO₃-10 nanofibers, displaying the highest response of 101.3 and the shortest response time (125 s)/recovery time (231 s) toward 3 ppm NO₂ at 90 °C. These excellent sensing characteristics were attributed to the high gas diffusion coefficient and strong absorbing capability for surface O₂⁻ species and NO₂ gas molecules, originating from the high porosity, high oxygen vacancy concentration, and high surface area of the WO₃-10 nanofibers.