A reversible electrochromic effect has been observed for the first time in flame spray pyrolysis (FSP) processed ε‐WO3 thin films without the use of an ion storage layer and an electrolytic layer. The dark coloration that appears upon the application of a voltage in films deposited on top of interdigitated gold electrodes is localized to the low voltage (−) electrode arm and it switches to the opposite arm upon a reversal of the polarity. Raman spectroscopy indicated that the coloration was not due to intercalation. It is argued here that the coloration is driven by the asymmetric ferroelectric properties of the ε‐WO3 crystals and that this electrochromic reversibility is intrinsically coupled with the polarization switching of the device.

The hexagonal WO3 polymorph, h-WO3, has attracted attention due to its interatomic channels, allowing for a greater degree of intercalation compared to other WO3 polymorphs. Our research group has previously demonstrated h-WO3 to be a highly sensitive gas sensing material for a flu biomarker, isoprene. In this work, the gas sensing performance of this polymorph has been further investigated in two distinct configurations of the material produced by different processing routes. The first sample was synthesized using Na2WO4∙2H2O and showed (100) faceting. The second sample was synthesized using WCl6 and showed (001) faceting. The gas sensing response of the nanostructured films deposited using the (100) textured h-WO3 sample 1 had a higher response to acetone at 350 °C. The (001) textured h-WO3 sample 2 favored isoprene at 350 °C. The selectivity of the latter to isoprene is explained in terms of the dangling bonds present on the (001) facets. The tungsten and oxygen dangling bonds present on the (001) plane favor the adsorption of the isoprene molecule over that of the acetone molecule due to the oxygen containing dipole present in the acetone molecule.

Scalable fabrication of freestanding carbon nanotube films (buckypapers) is of notable interest in nanotechnology due to emerging, real world applications for these lightweight and flexible materials. Post-electrophoretic deposition electrochemical separation (PEPDECS), a recently developed method for the scalable production of buckypapers, involves the electrophoretic deposition (EPD) of charged carbon nanotubes onto a flat substrate in a parallel-plate capacitor configuration, followed by a reversal of the direction of the electric field to detach the film. This study explored the characteristics of the deposition and liberation of the delaminated film, such as the applied voltage and the electrode size, in search of the optimum conditions for high quality buckypaper fabrication. Bubble formation on the film, due to the electrolysis of the suspension, increased as a function of the current density. The time required to delaminate a film completely from its underlying substrate was higher at higher initial current densities. Additionally, only when the applied EPD voltage was ≥2.8 V was the integrity of the buckypaper sufficient for them to be handled. The mechanical properties of the resulting films were examined to quantify their integrity. These experiments demonstrate the dependency of successful film fabrication on variable conditions during the initial EPD and provide a means to control the properties of the final films.