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.