Highly sensitive hydrogen sulfide (H₂S) gas sensors were developed from CuO-decorated ZnO semiconducting hierarchical nanostructures. The ZnO hierarchical nanostructure was fabricated by an electrospinning method following hydrothermal and heat treatment. CuO decoration of ZnO hierarchical structures was carried out by a wet method. The H₂S gas-sensing properties were examined at different working temperatures using various quantities of CuO as the variable. CuO decoration of the ZnO hierarchical structure was observed to promote sensitivity for H₂S gas higher than 30 times at low working temperature (200 °C) compared with that in the nondecorated hierarchical structure. The sensing mechanism of the hybrid sensor structure is also discussed. The morphology and characteristics of the samples were examined by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV-vis absorption, photoluminescence (PL), and electrical measurements.

We developed a facile method to fabricate highly porous Au-embedded WO₃ nanowire structures for efficient sensing of CH₄ and H₂S gases. Highly porous single-wall carbon nanotubes were used as template to fabricate WO₃ nanowire structures with high porosity. Gold nanoparticles were decorated on the tungsten nanowires by dipping in HAuCl₄ solution, followed by oxidation. The surface morphology, structure and electrical properties of the fabricated WO₃ and Au-embedded WO₃ nanowire structures were examined by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and current–voltage measurements. Formation of a nanowire structure resulted in significant enhancement in sensing response to H₂S and CH₄ gases. Furthermore, Au embedment into the WO₃ nanowire structures remarkably improved the performance of the sensors. The increase in response performance of sensors and adsorption–desorption kinetic processes on the sensing layers were discussed in relation with the role of Au embedment.

Zinc oxide (ZnO) hollow hemisphere (HS) and urchin-like (UL) structures were fabricated and examined for application to a gas sensor. Films of hollow ZnO-HS arrays floating over substrates were synthesized via Zn sputtering onto the template of a polystyrene sphere array followed by oxidation. Growing ZnO nanorods upon HS surfaces via a hydrothermal method formed hollow ZnO–UL structures. The thicknesses of the HS films and the lengths of nanorods in the UL structures were varied to obtain the maximum response to NO gas. Both sensor structures showed a sensing of tens of parts per billion of levels of NO concentrations with good response and gas selectivity. The highest response was realized through the thinness and the open porosity of the structures. The surface depletion determined the sensor response signal for the sensor geometry with the highest response.

A highly porous TiO₂–WO₃ core–shell nanowire structure for an electrochromic (EC) coating was fabricated by sputter deposition of titanium and tungsten on a porous single-walled carbon nanotube template. This process was followed by thermal oxidation. The morphology and crystalline quality of composite materials were investigated by scanning electron microscopy, X-ray diffraction, and transmission electron microscopy. The electrochemical and EC properties were also examined and compared with thin TiO₂–WO₃ composite films as well as individual WO₃ and TiO₂ nanowire structures. The highly porous composite nanowire structure showed a highly enhanced proton intercalation capacity with good reversible electrochemical cycling of intercalation–deintercalation. The nanostructure also showed significantly improved EC contrast and coloration efficiency. This enhancement was observed with high chemical stability of the material. We proposed an atomic model of proton insertion into oxygen vacancies to explain the EC property and gas sensing simultaneously.