Microstructure evolution of TiO2 gas sensors produced by electrospinning

Gas sensors produced by electrospinning demonstrate excellent performance in terms of sensitivity, reversibility, response and recovery time. These merits are formally attributed to their nanostructured fibrillar morphology and the relationship between microstructure and gas sensing properties. Thus, careful investigation is required to optimize the microstructure in order to achieve high gas sensing performance. In this work we study the microstructure evolution of nanostructured TiO2 gas sensors produced by electrospinning and examine the correlation between processing conditions, microstructure and gas sensing properties. Two distinguished TiO2 mesoporous morphologies were obtained, one with smaller grain size (29 nm) and higher specific surface area (71.4 m2/g) and the other with larger grain size (42 nm) and lower specific surface area (13.3 m2/g). The sensors displayed stable and reversible response to CO and NO2, with response and recovery time of several min. Two contributions to the overall impedance were observed, corresponding to the surface depletion region and the remaining bulk region. The surface impedance was found to be sensitive to CO and NO2 unlike the bulk impedance that displayed very little sensitivity to these gases. These results give new insight on the correlation between microstructure and gas sensing properties of electrospun TiO2 gas sensors.