Electrochromic properties of porous WO3-TiO2 core-shell nanowires

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.