This work presents a new route to suppress grain growth and tune the sensitivity and selectivity of nanocrystalline SnO2 fibers. Unloaded and Pd‐loaded SnO2 nanofiber mats are synthesized by ...electrospinning followed by hot‐pressing at 80 °C and calcination at 450 or 600 °C. The chemical composition and microstructure evolution as a function of Pd‐loading and calcination temperature are examined using EDS, XPS, XRD, SEM, and HRTEM. Highly porous fibrillar morphology with nanocrystalline fibers comprising SnO2 crystallites decorated with tiny PdO crystallites is observed. The grain size of the SnO2 crystallites in the layers that are calcined at 600 °C decreases with increasing Pd concentration from about 15 nm in the unloaded specimen to about 7 nm in the 40 mol% Pd‐loaded specimen, indicating that Pd‐loading could effectively suppress the SnO2 grain growth during the calcination step. The Pd‐loaded SnO2 sensors have 4 orders of magnitude higher resistivity and exhibit significantly enhanced sensitivity to H2 and lower sensitivity to NO2 compared to their unloaded counterparts. These observations are attributed to enhanced electron depletion at the surface of the PdO‐decorated SnO2 crystallites and catalytic effect of PdO in promoting the oxidation of H2 into H2O. These phenomena appear to have a much larger effect on the sensitivity of the Pd‐loaded sensors than the reduction in grain size.
Nanocrystalline SnO2 fibers are fabricated by electrospinning using Pd as a grain growth inhibitor and a catalyst for enhancing oxidation reactions. Pd‐loaded or unloaded (pristine) SnO2 fibers can be used as gas sensors capable of detecting trace concentrations as low as several parts per billion (ppb) of H2 and NO2, respectively.
Abstract
This work presents a new route to suppress grain growth and tune the sensitivity and selectivity of nanocrystalline SnO
2
fibers. Unloaded and Pd‐loaded SnO
2
nanofiber mats are synthesized ...by electrospinning followed by hot‐pressing at 80 °C and calcination at 450 or 600 °C. The chemical composition and microstructure evolution as a function of Pd‐loading and calcination temperature are examined using EDS, XPS, XRD, SEM, and HRTEM. Highly porous fibrillar morphology with nanocrystalline fibers comprising SnO
2
crystallites decorated with tiny PdO crystallites is observed. The grain size of the SnO
2
crystallites in the layers that are calcined at 600 °C decreases with increasing Pd concentration from about 15 nm in the unloaded specimen to about 7 nm in the 40 mol% Pd‐loaded specimen, indicating that Pd‐loading could effectively suppress the SnO
2
grain growth during the calcination step. The Pd‐loaded SnO
2
sensors have 4 orders of magnitude higher resistivity and exhibit significantly enhanced sensitivity to H
2
and lower sensitivity to NO
2
compared to their unloaded counterparts. These observations are attributed to enhanced electron depletion at the surface of the PdO‐decorated SnO
2
crystallites and catalytic effect of PdO in promoting the oxidation of H
2
into H
2
O. These phenomena appear to have a much larger effect on the sensitivity of the Pd‐loaded sensors than the reduction in grain size.
Abstract
This work presents a new route to suppress grain growth and tune the sensitivity and selectivity of nanocrystalline SnO
2
fibers. Unloaded and Pd‐loaded SnO
2
nanofiber mats are synthesized ...by electrospinning followed by hot‐pressing at 80 °C and calcination at 450 or 600 °C. The chemical composition and microstructure evolution as a function of Pd‐loading and calcination temperature are examined using EDS, XPS, XRD, SEM, and HRTEM. Highly porous fibrillar morphology with nanocrystalline fibers comprising SnO
2
crystallites decorated with tiny PdO crystallites is observed. The grain size of the SnO
2
crystallites in the layers that are calcined at 600 °C decreases with increasing Pd concentration from about 15 nm in the unloaded specimen to about 7 nm in the 40 mol% Pd‐loaded specimen, indicating that Pd‐loading could effectively suppress the SnO
2
grain growth during the calcination step. The Pd‐loaded SnO
2
sensors have 4 orders of magnitude higher resistivity and exhibit significantly enhanced sensitivity to H
2
and lower sensitivity to NO
2
compared to their unloaded counterparts. These observations are attributed to enhanced electron depletion at the surface of the PdO‐decorated SnO
2
crystallites and catalytic effect of PdO in promoting the oxidation of H
2
into H
2
O. These phenomena appear to have a much larger effect on the sensitivity of the Pd‐loaded sensors than the reduction in grain size.
This work presents a new route to suppress grain growth and tune the sensitivity and selectivity of nanocrystalline SnO2 fibers. Unloaded and Pd‐loaded SnO2 nanofiber mats are synthesized by ...electrospinning followed by hot‐pressing at 80 °C and calcination at 450 or 600 °C. The chemical composition and microstructure evolution as a function of Pd‐loading and calcination temperature are examined using EDS, XPS, XRD, SEM, and HRTEM. Highly porous fibrillar morphology with nanocrystalline fibers comprising SnO2 crystallites decorated with tiny PdO crystallites is observed. The grain size of the SnO2 crystallites in the layers that are calcined at 600 °C decreases with increasing Pd concentration from about 15 nm in the unloaded specimen to about 7 nm in the 40 mol% Pd‐loaded specimen, indicating that Pd‐loading could effectively suppress the SnO2 grain growth during the calcination step. The Pd‐loaded SnO2 sensors have 4 orders of magnitude higher resistivity and exhibit significantly enhanced sensitivity to H2 and lower sensitivity to NO2 compared to their unloaded counterparts. These observations are attributed to enhanced electron depletion at the surface of the PdO‐decorated SnO2 crystallites and catalytic effect of PdO in promoting the oxidation of H2 into H2O. These phenomena appear to have a much larger effect on the sensitivity of the Pd‐loaded sensors than the reduction in grain size.
The cover image shows a scanning electron microscopy image of nanocrystalline Pd‐loaded SnO2 gas sensors produced by electrospinning. SnO2 and PdO nanocrystallites are presented in yellow and orange, respectively, in the false‐color image of the fibers in front. On page 4258, Avner Rothschild, Il‐Doo Kim, and co‐workers demonstrate that Pd‐loading remarkably enhances the sensitivity to CO and reduces the sensitivity to NO2.
