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 WO 3 nanofibers . The porosity of WO 3 increased as the heating rate increased gradually up to 10 °C/min, but decreased after that value because of the destruction of WO 3 fiber-like structure. WO 3 nanofibers with a heating rate of 10 °C/min (WO 3 -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 NO 2 sensing performances of WO 3 were modulated by the heating rate. The best sensing performances were found for the WO 3 -10 nanofibers, displaying the highest response of 101.3 and the shortest response time (125 s)/recovery time (231 s) toward 3 ppm NO 2 at 90 °C. These excellent sensing characteristics were attributed to the high gas diffusion coefficient and strong absorbing capability for surface O 2 − species and NO 2 gas molecules, originating from the high porosity, high oxygen vacancy concentration, and high surface area of the WO 3 -10 nanofibers.